fswiki.us - User contributions [en]

Aerodynamic Basics

2021-08-17T23:03:53Z

U2berggeist: /* Low-Re effects */

Aerodynamics in FSAE can be used to describe the interaction of air and the racecar, in particular its bodywork and aerodynamic elements such as wings, diffusers and fins. It can be analysed by the use of [[Computational Fluid Dynamics]]. The performance of aerodynamic elements can be described by parameters such as the coefficient of Lift (<math>C_l</math>), coefficient of Drag (<math>C_d</math>) and the ratio of <math>C_l/C_d</math>.
==Conceptual aspect of Aerodynamics==
Aerodynamics is not necessary to make a car go around a racetrack. Check beforehand if your car benefits from aerodynamic elements. Simple laptime simulation usually includes lift and drag coefficents and helps you determine your target goals.
==Key Parameters==

Coefficient of Lift, <math>C_l</math>

Coefficient of Drag, <math>C_d</math>

Lift to Drag ratio, <math>C_l/C_d</math>

== Boundary Layers ==

There are many resources available about what exactly boundary layers are, why they exist, and other useful information. This will focus on FSAE applications, as they are fairly unique.

Beyond "what is a boundary layer" type questions, I ''highly'' recommend reading ''High Lift Aerodynamics''<ref>A. Smith, “High Lift Aerodynamics,” Journal of Aircraft, vol. 12, no. 6, pp. 501–539, 1975, doi:
[https://doi.org/10.2514/3.59830 10.2514/3.59830]</ref>, as it contains many of the fundamentals for the limitations of downforce generation. Most of what follows is a summary of the paper.

=== Laminar, Turbulent, and Transition ===

* Boundary layers (BL) can be either laminar, or turbulent
** Neither is "worse" or "better" than the other. They are simply different and have different effects aero systems.
* When a BL initially forms, it is laminar. Gradually fluctuations destabilize the flow and it becomes turbulent.
** This is known as '''(BL) transition'''
* The fluctuations may come naturally (from atmospheric turbulence or surface imperfections) or be induced artificially by "BL trips" or vortex generators
** The artificial methods force the transition to occur sooner than it would otherwise

* Determining when a boundary layer transitions is a function of it's Reynolds Number, <math>Re_x</math>, using <math>x</math> (distance along a wall) as its characteristic length scale
** The higher the Reynolds number the more likely it is to be turbulent (over a certain level, it is more-or-less guaranteed)
** Therefore, increasing flow velocity decreases the distance at which BL transition occurs

=== Pressure Gradients and Separation ===
* Flow separation occurs as a direct result of the existence of boundary layers
** Hence why "flow separation" and "boundary layer separation" are synonymous
* Pressure gradients describe the force being applied to the fluid as it moves
** A pressure gradient that pushes ''with'' the (bulk) fluid motion is known as a '''Favorable Pressure Gradient (FPG)'''
** A pressure gradient that pushes ''against'' the (bulk) fluid motion is known as an '''Adverse Pressure Gradient (APG)'''
* APGs are what cause flow separation
** The APG pushes against the boundary layer such that the flow close to the wall (which is significantly slower than the flow outside the BL) begins to move backwards

=== Low-<math>Re</math> effects ===
* Laminar and Turbulent BL react to APGs differently:
** '''''Laminar BLs are more susceptible to separation than turbulent BLs'''''

* Airfoils feature an initial FPG, followed by an APG (also known as '''pressure recovery''')
* If the Reynolds number is high enough for an airfoil, BL transition occurs before the APG region
** This means that the "stronger" turbulent BL will resist the APG well
** If the Reynolds number is too low, the BL will not transition and a (weak) laminar BL will be forced to go through the APG region.
** '''''FSAE cars generally run in this Low-<math>Re</math> regime'''''

* Low-<math>Re</math> phenomenon include:
** "Premature" separation (compared to running the airfoil at higher <math>Re</math>)
** Hysteresis
*** The AoA at which separation occurs is different when increasing AoA than decreasing AoA
*** See the [https://m-selig.ae.illinois.edu/uiuc_lsat.html UIUC LSAT database] for plots demonstrating this effect (ie. compare the differences in polar plots between different <math>Re</math>)

* Unless you're airfoil is operating outside the Low-<math>Re</math> regime (generally around <math>Re_c \approx 25,000</math>, though this is airfoil dependent), use airfoils explicitly designed for Low-<math>Re</math> regime
** These are meant to place the boundary layer transition point ahead of the APG region of the airfoil (or to "help" the BL transition sooner)
** S1223 airfoil is the quintessential airfoil design for this regime (at least for high lift applications, as would be found in FSAE cars)

'''Important Note for CFD:'''
* Low-<math>Re</math> effects are generally ''NOT'' captured by CFD, as all common turbulence models treat the BL as always turbulent.
** There are special "transition" models, but they require empirical calibration to work correctly
** Even if you have the empirical calibration data, BL transitions is ''very'' sensitive to surface roughness, surface shape, atmospheric conditions, etc.
** My advice is to simply trust wind tunnel data (such as [https://m-selig.ae.illinois.edu/uiuc_lsat.html UIUC LSAT]) to determine whether airfoils operating in Low-<math>Re</math>. If they are not, then the CFD assumptions aren't broken. If they are, then don't rely on CFD.

==Downforce==
[[Category:Body and Aero]]

Aerodynamic Basics

2021-08-17T23:02:15Z

U2berggeist: /* Boundary Layers */

Aerodynamics in FSAE can be used to describe the interaction of air and the racecar, in particular its bodywork and aerodynamic elements such as wings, diffusers and fins. It can be analysed by the use of [[Computational Fluid Dynamics]]. The performance of aerodynamic elements can be described by parameters such as the coefficient of Lift (<math>C_l</math>), coefficient of Drag (<math>C_d</math>) and the ratio of <math>C_l/C_d</math>.
==Conceptual aspect of Aerodynamics==
Aerodynamics is not necessary to make a car go around a racetrack. Check beforehand if your car benefits from aerodynamic elements. Simple laptime simulation usually includes lift and drag coefficents and helps you determine your target goals.
==Key Parameters==

Coefficient of Lift, <math>C_l</math>

Coefficient of Drag, <math>C_d</math>

Lift to Drag ratio, <math>C_l/C_d</math>

== Boundary Layers ==

There are many resources available about what exactly boundary layers are, why they exist, and other useful information. This will focus on FSAE applications, as they are fairly unique.

Beyond "what is a boundary layer" type questions, I ''highly'' recommend reading ''High Lift Aerodynamics''<ref>A. Smith, “High Lift Aerodynamics,” Journal of Aircraft, vol. 12, no. 6, pp. 501–539, 1975, doi:
[https://doi.org/10.2514/3.59830 10.2514/3.59830]</ref>, as it contains many of the fundamentals for the limitations of downforce generation. Most of what follows is a summary of the paper.

=== Laminar, Turbulent, and Transition ===

* Boundary layers (BL) can be either laminar, or turbulent
** Neither is "worse" or "better" than the other. They are simply different and have different effects aero systems.
* When a BL initially forms, it is laminar. Gradually fluctuations destabilize the flow and it becomes turbulent.
** This is known as '''(BL) transition'''
* The fluctuations may come naturally (from atmospheric turbulence or surface imperfections) or be induced artificially by "BL trips" or vortex generators
** The artificial methods force the transition to occur sooner than it would otherwise

* Determining when a boundary layer transitions is a function of it's Reynolds Number, <math>Re_x</math>, using <math>x</math> (distance along a wall) as its characteristic length scale
** The higher the Reynolds number the more likely it is to be turbulent (over a certain level, it is more-or-less guaranteed)
** Therefore, increasing flow velocity decreases the distance at which BL transition occurs

=== Pressure Gradients and Separation ===
* Flow separation occurs as a direct result of the existence of boundary layers
** Hence why "flow separation" and "boundary layer separation" are synonymous
* Pressure gradients describe the force being applied to the fluid as it moves
** A pressure gradient that pushes ''with'' the (bulk) fluid motion is known as a '''Favorable Pressure Gradient (FPG)'''
** A pressure gradient that pushes ''against'' the (bulk) fluid motion is known as an '''Adverse Pressure Gradient (APG)'''
* APGs are what cause flow separation
** The APG pushes against the boundary layer such that the flow close to the wall (which is significantly slower than the flow outside the BL) begins to move backwards

=== Low-<math>Re</math> effects ===
* Laminar and Turbulent BL react to APGs differently:
** '''''Laminar BLs are more susceptible to separation than turbulent BLs'''''

* Airfoils feature an initial FPG, followed by an APG (also known as '''pressure recovery''')
* If the Reynolds number is high enough for an airfoil, BL transition occurs before the APG region
** This means that the "stronger" turbulent BL will resist the APG well
** If the Reynolds number is too low, the BL will not transition and a (weak) laminar BL will be forced to go through the APG region.
** '''''FSAE cars generally run in this Low-<math>Re</math> regime'''''

* Low-<math>Re</math> phenomenon include:
** "Premature" separation (compared to running the airfoil at higher <math>Re</math>
** Hysteresis
*** The AoA at which separation occurs is different when increasing AoA than decreasing AoA
*** See the [https://m-selig.ae.illinois.edu/uiuc_lsat.html UIUC LSAT database] for plots demonstrating this effect (ie. compare the differences in polar plots between different <math>Re</math>)

* Unless you're airfoil is operating outside the Low-<math>Re</math> regime (generally around <math>Re_c \approx 25,000</math>, though this is airfoil dependent), use airfoils explicitly designed for Low-<math>Re</math> regime
** These are meant to place the boundary layer transition point ahead of the APG region of the airfoil (or to "help" the BL transition sooner)
** S1223 airfoil is the quintessential airfoil design for this regime (at least for high lift applications, as would be found in FSAE cars)

'''Important Note for CFD:'''
* Low-<math>Re</math> effects are generally ''NOT'' captured by CFD, as all common turbulence models treat the BL as always turbulent.
** There are special "transition" models, but they require empirical calibration to work correctly
** Even if you have the empirical calibration data, BL transitions is ''very'' sensitive to surface roughness, surface shape, atmospheric conditions, etc.
** My advice is to simply trust wind tunnel data (such as [https://m-selig.ae.illinois.edu/uiuc_lsat.html UIUC LSAT]) to determine whether airfoils operating in Low-<math>Re</math>. If they are not, then the CFD assumptions aren't broken. If they are, then don't rely on CFD.

==Downforce==
[[Category:Body and Aero]]

Aerodynamic Basics

2021-08-17T22:41:40Z

U2berggeist: /* Boundary Layers */ Quick expansion

Computational Fluid Dynamics

2020-08-24T22:35:33Z

U2berggeist: /* Discretization */

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand where errors come from and (thus) how to mitigate/fix them.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

Results are more than useless without a mesh refinement study. With one, their slightly more useful.

== Solution ==

Description of order of accuracy considerations and convergence criteria

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the Data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]
[[Category:Software]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

Computational Fluid Dynamics

2020-08-24T22:34:29Z

U2berggeist: /* Fun Acronyms */

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand where errors come from and (thus) how to mitigate/fix them.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

== Solution ==

Description of order of accuracy considerations and convergence criteria

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the Data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]
[[Category:Software]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

Computational Fluid Dynamics

2020-08-24T22:33:53Z

U2berggeist:

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand where errors come from and (thus) how to mitigate/fix them.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

== Solution ==

Description of order of accuracy considerations and convergence criteria

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]
[[Category:Software]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

Aerodynamic Basics

2020-08-18T21:45:16Z

U2berggeist:

Thread:User talk:Emilyanthony/Category for Engineering Tools

2020-08-18T21:37:22Z

U2berggeist: New thread: Category for Engineering Tools

Maybe it'd be nice to have a general category for engineering tools. Ie. CFD, (structural) FEA, track time simulation, vehicle dynamic simulation, engine simulation, etc.

I currently wrote a more general simulation statement on the CFD page, but I think that might be better placed in a general computer simulation page. Thoughts?

Aerodynamic Basics

2020-08-18T21:33:03Z

U2berggeist: Move paper citation to reference

Aerodynamic Basics

2020-08-18T21:23:59Z

U2berggeist: Add notes for Boundary Layer section

Computational Fluid Dynamics

2020-08-18T21:15:26Z

U2berggeist: /* Solution */

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand where errors come from and (thus) how to mitigate/fix them.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

== Solution ==

Description of order of accuracy considerations and convergence criteria

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

Aerodynamic Basics

2020-08-18T21:08:49Z

U2berggeist:

Aerodynamic Basics

2020-08-18T21:07:46Z

U2berggeist: Update math formatting

Aerodynamics in FSAE can be used to describe the ineraction of air and the racecar, in particular its bodywork and aerodynamic elements such as wings, diffusers and fins. It can be analysed by the use of [[Computational Fluid Dynamics]]. The performance of aerodynamic elements can be described by parameters such as the coefficient of Lift (<math>C_l</math>), coefficient of Drag (<meta http-equiv="content-type" content="text/html; charset=utf-8"><math>C_d</math>) and the ratio of <meta http-equiv="content-type" content="text/html; charset=utf-8"><math>C_l/C_d</math>.
==Conceptual aspect of Aerodynamics==
Aerodynamics is not necessary to make a car go around a racetrack. Check beforehand if your car benefits from aerodynamic elements. Simple laptime simulation usually inclues lift and drag coefficents and helps you determine your target goals.
==Key Parameters==
Coefficient of Lift,<meta http-equiv="content-type" content="text/html; charset=utf-8"><math>C_l</math>

Coefficient of Drag,<meta http-equiv="content-type" content="text/html; charset=utf-8"><math>C_d</math>

Lift to Drag ratio,<meta http-equiv="content-type" content="text/html; charset=utf-8"><math>C_l/C_d</math>

==Downforce==
[[Category:Body and Aero]]

Airfoils

2020-08-18T20:46:21Z

U2berggeist:

==Parts of an Airfoil==
===Leading Edge===
The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.
===Trailing Edge===
The trailing edge is the furthest rearward edge of the airfoil.
===Chord===
The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE. The chord line often serves as the reference datum for airfoils defined by coordinates.
===Camber===
The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.
==Airfoil Selection==
Airfoils are available in various shapes and forms and the right airfoil may not even exist for your application. To get an understanding of the variety of airfoils you should check databases such as [http://airfoiltools.com/search/index airfoiltools].

Airfoils can be compared by different key parameters such as <math>C_l</math>, <math>C_d</math>, <math>C_m</math> and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). The Reynolds number is given as: <math display="block">Re = \frac{\rho u_\infty C}{\mu} = \frac{u_\infty C}{\nu}</math> , where <math>C</math> is the chord length, <math>\nu</math> is the kinematic viscosity, and <math>u_\infty</math> is the free stream velocity. To check the Reynolds number on your design visit [http://airfoiltools.com/calculator/reynoldsnumber airfoiltools Reynolds number calculator].
==Additional Parts==
===Endplates===
In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:
=====Louvers=====
Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.
=====Slats=====
Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.
===Supports===
When designing supports, it is important to take into account deflection and adjustablity

[[Category:Body and Aero]]

Computational Fluid Dynamics

2020-08-18T20:35:07Z

U2berggeist:

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand where errors come from and (thus) how to mitigate/fix them.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

== Solution ==

Description of order of accuracy considerations

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

Computational Fluid Dynamics

2020-08-18T20:34:19Z

U2berggeist: Added intro and general framework for page.

'''Computational Fluid Dynamics (CFD)''' is the method by which fluid flow can be simulated using computational methods. It generally involves discretizing the Navier-Stokes equations (partial differential equations that govern fluid motion) into series of algebraic equations that can then be solved.

In a Formula SAE/Student context, CFD is predominantly used for two purposes; simulating an external aerodynamics package (including radiators and other cooling components) and simulating the intake and exhaust systems of internal combustion engines. While either problem have their unique challenges, the process of running CFD for their simulation it quite similar.

As with all computational simulations (CFD, structural simulation, track time simulators, etc.), they break down into series of steps which introduce their own sources of error (there will be error and you ''must'' account for it):

# Idealization
# Discretization
# Solution

Idealization are the physical assumptions made to come to some mathematical model. Discretization is the process of breaking up that mathematical model into a series of smaller, simpler problems. Solution is the process of actually solving those smaller problems. The errors associated with each step are modeling errors, discretization errors, and numerical errors, respectively (though the latter two are often grouped together). While this wiki page won't go into these steps in detail (it's worthy of a textbook), it's important to understand this.

== Modeling (Idealization) ==

=== Turbulence Modeling ===

=== Other Physical Assumptions ===

== Discretization ==

Finite Volume is by far the most popular discretization method for fluid problems, though Finite Difference and Finite Element methods are equally applicable.

Beyond discretization method, geometric and fluid feature resolution are very important.

<math>y^+</math> is important near the wall

== Solution ==

Description of order of accuracy considerations

== Solvers ==

ANSYS, Star CCM, OpenFOAM, SimScale (which is just cloud based OpenFOAM).

==Fun Acronyms==

* Colorful Fluid Dynamics
* Can't Fit the data.
* Conspiracy Fraud Deceit

[[Category:Body and Aero]]
[[Category:Internal Combustion]]

probably should have notes on meshing, model selection (suggested and why), analysis/postprocessing

User:U2berggeist

2020-08-18T20:13:21Z

U2berggeist: Created page with "James Wright Chief Engineer at Clemson University for two years, Lead aero guy for 2 years. Currently working on PhD in turbulence modeling (ie. CFD)."

James Wright

Chief Engineer at Clemson University for two years, Lead aero guy for 2 years. Currently working on PhD in turbulence modeling (ie. CFD).

Airfoils

2020-08-18T20:06:12Z

U2berggeist: /* Chord */

==Parts of an Airfoil==
===Leading Edge===
The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.
===Trailing Edge===
The trailing edge is the furthest rearward edge of the airfoil.
===Chord===
The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE. The chord line often serves as the reference datum for airfoils defined by coordinates.

===Camber===
The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.
==Airfoil Selection==
Airfoils are available in various shapes and forms and the right airfoil may not even exist for your application. To get an understanding of the variety of airfoils you should check databases such as [http://airfoiltools.com/search/index airfoiltools].

Airfoils can be compared by different key parameters such as <math>C_l</math>, <math>C_d</math>, <math>C_m</math> and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). The Reynolds number is given as: <math display>Re = \frac{\rho u_\infty C}{\mu} = \frac{u_\infty C}{\nu}</math> , where <math>C</math> is the chord length, <math>\nu</math> is the kinematic viscosity, and <math>u_\infty</math> is the free stream velocity. To check the Reynolds number on your design visit [http://airfoiltools.com/calculator/reynoldsnumber airfoiltools Reynolds number calculator].
==Additional Parts==
===Endplates===
In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:
=====Louvers=====
Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.
=====Slats=====
Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.
===Supports===
When designing supports, it is important to take into account deflection and adjustablity

[[Category:Body and Aero]]

Airfoils

2020-08-18T20:04:45Z

U2berggeist: Remove erroneous statement. I'm not sure what the sentence is supposed to mean and can't figure out an appropriate interpretation.

==Parts of an Airfoil==
===Leading Edge===
The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.
===Trailing Edge===
The trailing edge is the furthest rearward edge of the airfoil.
===Chord===
The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE.
===Camber===
The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.
==Airfoil Selection==
Airfoils are available in various shapes and forms and the right airfoil may not even exist for your application. To get an understanding of the variety of airfoils you should check databases such as [http://airfoiltools.com/search/index airfoiltools].

Airfoils can be compared by different key parameters such as <math>C_l</math>, <math>C_d</math>, <math>C_m</math> and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). The Reynolds number is given as: <math display>Re = \frac{\rho u_\infty C}{\mu} = \frac{u_\infty C}{\nu}</math> , where <math>C</math> is the chord length, <math>\nu</math> is the kinematic viscosity, and <math>u_\infty</math> is the free stream velocity. To check the Reynolds number on your design visit [http://airfoiltools.com/calculator/reynoldsnumber airfoiltools Reynolds number calculator].
==Additional Parts==
===Endplates===
In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:
=====Louvers=====
Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.
=====Slats=====
Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.
===Supports===
When designing supports, it is important to take into account deflection and adjustablity

[[Category:Body and Aero]]

Airfoils

2020-08-18T20:03:09Z

U2berggeist: Improved formatting

==Parts of an Airfoil==
===Leading Edge===
The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.
===Trailing Edge===
The trailing edge is the furthest rearward edge of the airfoil.
===Chord===
The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE.
===Camber===
The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.
==Airfoil Selection==
Airfoils are available in various shapes and forms and the right airfoil may not even exist for your application. To get an understanding of the variety of airfoils you should check databases such as [http://airfoiltools.com/search/index airfoiltools].

Airfoils can be compared by different key parameters such as <math>C_l</math>, <math>C_d</math>, <math>C_m</math> and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). The Reynolds number is given as: <math display>Re = \frac{\rho u_\infty C}{\mu} = \frac{u_\infty C}{\nu}</math> , where <math>C</math> is the chord length, <math>\nu</math> is the kinematic viscosity, and <math>u_\infty</math> is the free stream velocity. Two airfoils with the same Reynolds number perform similar. To check the Reynolds number on your design visit [http://airfoiltools.com/calculator/reynoldsnumber airfoiltools Reynolds number calculator].

==Additional Parts==
===Endplates===
In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:
=====Louvers=====
Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.
=====Slats=====
Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.
===Supports===
When designing supports, it is important to take into account deflection and adjustablity

[[Category:Body and Aero]]

Airfoils

2020-08-18T19:49:43Z

U2berggeist: /* Airfoil Selection */

==Parts of an Airfoil==
===Leading Edge===
The leading edge of an airfoil is the first part of the airfoil in the free stream. It will change with the angle of attack (AoA) of the airfoil.
===Trailing Edge===
The trailing edge is the furthest rearward edge of the airfoil.
===Chord===
The chord of an airfoil is the distance from leading edge to trailing edge. It is measured by drawing a straight line from the LE to TE.
===Camber===
The camber of an airfoil measures its shape. The camber line is drawn from the leading edge to the trailing edge, staying equidistant from the top and bottom surfaces of the airfoil at each point. The camber at each point is thus the distance from the camber line to either the top or bottom surface of the airfoil. For a symmetric airfoil, the camber line and the chord line are the same.
==Airfoil Selection==
Airfoils are available in various shapes and forms and the right arifoil may not even exist for your application. To get an understanding of the variety of arifoils you should check databases such as [http://airfoiltools.com/search/index airfoiltools].

Airfoils can be compared by different key parameters such as Cl, Cd, Cm and the change of these parameters over the angle of attack. To compare an airfoil, the Reynolds number gives an insight on the ratio of chord length to airspeed (simplified). Two airfoils with the same Reynolds number perform similar. To check the Reynolds number on your design visit [http://airfoiltools.com/calculator/reynoldsnumber airfoiltools Reynolds number calculator]. For manual calculation use the formula Re = (fluid density * free stream velocity * chord length) / dynamic viscosity of the fluid.

==Additional Parts==
===Endplates===
In a standard wing with no endplates, the wing experiences induced drag due to the high pressure region above the wing coming around the edge to the low pressure region below the wing. This creates vortices and adds extra drag to the vehicle. In a plane, the aspect ratio of the wing can be increased to limit this effect (think about a glider, they frequently have really long wings with a short chord, increasing wing span while limiting wing area).

For our vehicles, we cannot extend our wings outside of our wheels, and thus need to find a different solution to limit our induced drag. Adding endplates physically prevents the high pressure and low pressure region from interacting, thereby reducing the drag generated from this effect. Sadly, endplates can generate their own drag through similar effects. The high pressure ambient air can "spill over" into the low pressure region captured inside the endplates, creating vortices and drag.

There are a few different methods to reducing this drag:
=====Louvers=====
Louvers are small cuts in the endplate, generally found above the mainplane and in front of the flaps. These cuts allow some of the high pressure air in this region to escape, which lowers the overall pressure in this area. Lowering the pressure can reduce the downforce generated, but can also reduce drag by limiting the strength of the created vortices.
=====Slats=====
Slats are generally found below the flaps and behind the mainplane, toward the rear bottom corner of the endplates. These slats allow some of the low pressure air to escape, thereby reducing the downforce and drag generated, similar to the louvers.
===Supports===
When designing supports, it is important to take into account deflection and adjustablity

[[Category:Body and Aero]]