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F1 in Schools: Virtual Wind Tunnel Application
Formula One Class

by James Stewart, CHAM Ltd.
May 2013

Contents

  1. Introduction
  2. Purpose of the Scenario
  3. Adjustable Parameters
    1. Geometry Parameters
      1. Car Body
      2. Wheel Settings
      3. C02 Canister Settings
    2. Boundary Conditions
    3. Numerical Settings
  4. Running a Simulation
  5. Viewing the Results
  6. Tutorials

1. Introduction

The Formula One in Schools challenge is split into two main competition classes, namely, the Bloodhound SSC Class and the Formula One Class. CHAM's F1 in Schools: Virtual Wind Tunnel package has been designed to allow users to test their competition model designs under the regulations for their chosen competition class.

The full technical regulations for each class can be downloaded from the F1 in Schools website with the Bloodhound SSC Class regulations available here, and the Formula One Class regulations available here. In addition, the full competition rules can be downloaded here.

This document will briefly describe the F1-VWT: Formula One Class Scenario. For the full F1-VWT User Guide, please see here.

Alternatively, the F1-VWT can be used to investigate Bloodhound SSC Class model designs. This can be achieved by closing the F1-VWT interface and selecting Bloodhound SSC Class from the main interface seen below:

2. Purpose of the Scenario

The F1-VWT: Formula One Class scenario has been designed to aid students competing in the Formula One Class of the F1 in Schools challenge. During the analysis phase of the project, Virtual Wind Tunnel Technology can be used to provide far greater flexibility for investigating model designs and the impact which design changes may have on the aerodynamic performance of the model car.

Any number of designs can be tested in the F1-VWT environment without the need to manufacture a single model. Thus, not only does the F1-VWT package offer more flexible use, it also provides a much cheaper and less time consuming means of performing aerodynamic analysis whilst providing far more detailed results.

The purpose of the Formula One Class subdivision of the F1-VWT is to allow students competing within this class to test their models under the constraints of the technical regulations for the Formula One Class (See here for more details). In-built within the class scenario are appropriate legality checks to be considered when designing a Formula One Class model.

3. Adjustable Parameters

The Formula One Class scenario is specifically designed to allow users easy access to the parameters governing the scenario case. The F1-VWT package displays such parameters within several simple parameter groups. Each parameter within a group can be altered according to the users' needs.

When a user has selected and begun the Formula One Class scenario, the F1-VWT interface will appear as in the image above. Selecting the 'Inspect or modify input data' tab from near the top of the interface will cause the following to appear:

The buttons located within the left-hand border of the interface, as seen above, refer to the specific parameter groups which contain the settings for the case.

3.1 Geometry Parameters

For the Formula One Class, the geometry parameters which govern the case are divided into three distinct parameter groups, namely: 'Car Body'; 'Wheel Settings' and 'C02 Canister Settings'. These three parameter groups can be accessed by clicking the appropriate buttons from the left-hand panel of the interface. The parameters contained within each group will briefly be discussed here.

3.1.1 Car Body

The 'Car Body' parameter group can be used to adjust the size and shape of the model geometry used for the current case. The F1-VWT has some preset test geometries, accessed via the drop-down menu beside the parameter 'body geometry file'. If a custom geometry is to be imported for the simulation, the 'body geometry file' parameter should be set to 'custom' and then the file name of the desired geometry file can be entered within the white box corresponding to the parameter 'custom geometry file'.

The settings seen within the image below indicate that the custom CAD geometry file named f1car.stl is to be used for the case.

NOTE: Any custom CAD file to be used within the F1-VWT must be placed within the directory: %PHOENICS%\d_sapps\F1-VWT\Working (or a subdirectory thereof) where %PHOENICS% is set to the drive on which the F1-VWT is installed, e.g. C:\phoenics.

The 'geometry rotation position' parameter is by default set to 1. This parameter refers to the PHOENICS VR-Editor standard rotation options. When using any of the default models, this parameter will not need to be changed. However, it is possible that a custom CAD geometry may be imported with the incorrect orientation, in which case this parameter should be adjusted until the desired model orientation is achieved.

The next three parameters govern the size of the car body. To adjust these values the user must simply enter the desired value within the appropriate white box.

NOTE: The car dimensions are bound by the F1 in Schools technical regulations. The F1-VWT includes provisions to check that the model set-up adheres to the competition rules. When the user checks the set-up (this should always be done before running the case) a window similar to that seen below will appear with any warnings of rule contravention. If the user does not adjust the settings to ensure that their model is legal, the F1-VWT will automatically use default values for the simulation where necessary.

The final parameter of this group, 'competition class' indicates the current F1 in Schools competition class being simulated. The default value is set according to the user's scenario selection made from the main interface seen below:

If a user wishes to change competition class, the scenario window should be closed and the desired class can be selected from the main interface seen above.

3.1.2 Wheel Settings

Selecting the 'Wheel Settings' button from the left-hand panel of the interface will cause the following to appear:

The first parameter appearing within this group gives the user the option of whether to 'use and display wheels?' within the case. The user can then select 'true' or 'false'. If 'false' is selected, no wheels will be added to the case and the remaining parameters within the 'Wheel Settings' group will have no effect on the case set-up.

When importing a custom CAD geometry, it is highly likely that the model will include wheels and thus, in such a case, users should set the 'use and display wheels?' parameter to 'false'.

Provided wheels are being added to the case, the next four parameters govern the wheel diameter and width. These values can be adjusted by simply entering the desired value in the appropriate white box.

The next two parameters, 'front axle position from defaults' and 'rear axle position from default' govern the front and rear axle positions relative to their default locations. The default wheel positions are set automatically. Entering a positive value for either of these parameters will move the appropriate wheelset towards the front of the car and a negative value will move the appropriate wheelset towards the rear of the car.

The final two parameters, 'front axle extension from default' and 'rear axle extension from default', govern the front and rear axle lengths. This determines how far apart the wheels are. By default the case has been set up to place the wheels 5mm away from the car body in accordance with the F1 in Schools rules. Increasing these parameters will place the wheels further away from the car body and decreasing them will bring the wheels closer together.

NOTE: The wheel dimensions for the case are also bound by the competition technical regulations. The F1-VWT attempts to inform the user of any rule contraventions but to ensure that your model complies with the competition rules, please visit the F1 in Schools website here.

3.1.3 C02 Canister Settings

Clicking on the 'C02 Canister Settings' button from the left-hand panel of the F1-VWT interface causes the following to appear:

The first parameter within this group, 'use and display co2 canister?', is used to switch on or off the display and use of the CO2 bottle within the simulation. If set to 'false', the remaining parameters within this group will have no effect on the case. However, if the C02 Canister is being used within the case, then the 'height of co2 canister' parameter is used to set the height of the CO2 bottle within the display.

NOTE: The height of the C02 canister is bound by the competition technical regulations. The F1-VWT attempts to inform the user of any rule contraventions but to ensure that your model complies with the competition rules, please visit the F1 in Schools website here.

3.2 Boundary Conditions

Clicking on the 'Wind Speed' button from the left-hand panel of the interface accesses the boundary condition settings for the case, as seen below:

As can be seen from above, there exists the single 'tunnel wind speed' parameter as the sole boundary condition for the case. By default the wind speed is set to 18 m/s. Should a user wish to alter this, they can simply type the desired value within the white box to reset the speed for the simulation case.

3.3 Numerical

Clicking the 'Numerical' button from the left-hand panel of the interface will cause the following to appear:

The first parameter, 'no. of iterations (sweeps)', governs the number of iterations (or sweeps) to be performed by the solver. Users can simply enter the desired value within the white box. More information about the PHOENICS Solver - EARTH can be found within the F1-VWT User Guide, located here.

The next parameter, 'select grid type', allows the user to specify which grid should be used for the simulation. A user can make their selection by activating the drop-down menu and clicking on the value they desire. The options for the F1-VWT scenario include preset coarse, medium and fine grids as well as a user_set option.

The coarse, medium and fine grid options vary in the number of computational cells which the grid comprises of. Using a coarse grid will reduce accuracy and overall simulation duration, whereas a fine grid will have the opposite effect. If a prese grid type is selected, the remaining parameters within the 'Numerical' group will have no effect on the case set-up.

If the user_set grid option is chosen, the remaining parameters within the 'Numerical' group can be used to adjust the number of cells used. Each of these remaining parameters provides the number of cells within a particular geomeical region of the Virtual Wind Tunnel environment. Any of these values can be adjusted by simply entering the desired value within the appropriate white box.

4. Running a Simulation

Once happy with the parameter settings for the case, it is advisable to check the set-up. To do this, simply click on the 'Display Scenario' button from the top-menu of the interface as indicated below:

After clicking on the 'Display Scenario' button, a PHOENICS VR-Editor window will appear, displaying the current case set-up. At this point, messages about any broken F1 in Schools rules will appear, allowing the user to ammend the errors before proceeding to run the simulation.

Once satisfied that all of the input settings have been make correctly, the user simply has to click the 'Run the simulation' button to begin the simulation of the case. After doing so, the solver will automatically be launched and the simulation will begin. When this happens, an image similar to the following will appear:

5. Viewing the Results

Using the Results File

By default, the PHOENICS result file will be opened automatically within the F1-VWT window under the 'View file:' tab. Within this file users will find an abundance of information relating to the most recently run simulation. Scrolling down the results file, the user will eventually come to a point where the integrated drag coefficients, axle loadings and the forces results are stored, this will typically appear as follows:

The fundamental aims for improving aerodynamic performance of racing cars is to minimise the integrated drag coefficient in the direction of motion, in the case of the F1-VWT that would be in the x-direction, indicated by 'Drag - Cdx' in the above image, and to maximise the negative lift, otherwise known as downforce, acting on the car, here denoted 'Lift - Cdz'.

The more downforce that can be created, the greater the traction of the car, and the smaller the drag coefficient, the lesser the air resistance acting on the car. Utilising the F1 in Schools Virtual Wind Tunnel package allows users to make minor adjustments to their models, re-import their geometries and re-run the simulations very simply and efficiently in order to optimise the drag and lift forces acting on their car design to obtain the greatest performance level come race day.

Viewing Results Graphically

Once a simulation run has been completed and the result file has been loaded for viewing, the 'Display results graphically' button becomes active on the top menu of the scenario case window (fifth from the left). Clicking this button launches the PHOENICS-VR Viewer with a window asking which files should be used for plotting. By default the 'Latest dumped files' are selected and so users can simply click 'OK' to continue to the graphical display of results.

Once within the PHOENICS VR-Viewer environment, users will be prompted to indicate whether they wish to run the in-built F1-VWT Post-Processing Macro. Clicking 'OK' when prompted will run the macro and images will begin to be produced automatically with a simple click on another 'OK' button required to move to the next image. Clicking 'Cancel' at any time will abort the macro run and leave the PHOENICS VR-Viewer displaying the current image.

All of the images are automatically dumped as image files within the F1-VWT working directory. A typical plot from the macro will look as follows, where the velocity contours are displayed on the car body and the F1-VWT floor surface:

Alternatively, should users wish to create their own graphical displays of results, they are free to do so. This can be achieved either:

  1. Following the previously outlined procedure for accessing the macro results and clicking 'Cancel' before the macro has begun. This then leaves the user with free reign of the PHOENICS VR-Viewer to create plots as they wish.
  2. By right-clicking the 'Display results graphically' button and selecting 'VR-Viewer' to launch the standard PHOENICS VR-Viewer without the macro content. Again, users are then free to creat plots as they wish.
  3. 3. Right-clicking the 'Display results graphically' button and selecting 'PHOTON' to launch an alternative viewing application.

More information about creating plots within the PHOENICS VR-Viewer can be found here. Information about the use of PHOTON can be found here.

6. Tutorials

For more information about the F1-VWT user-interface and how it can be used to set up and run an F1 in Schools Virtual Wind Tunnel Study, please consult the F1-VWT User Guide located here.

In addition to running a single case set-up, the F1-VWT has the unique capacity to set up and perform Multi-Run cases in which a sequence of simulations is erformed to determine the effect of certain parameter adjustments. A full F1-VWT: Formula One Class Multi-Run Tutorial can be found here.