CFD Analysis

A key component to KVRC lays in the Computational Fluid Dynamics (CFD) analysis undertaken on the racing cars to establish their aerodynamic performances.

Disclaimer

Prior to reading further, please note that:

Computer simulation provides an estimate of performance. This estimate is based on a necessarily simplified and idealised version of the racing car that does not and cannot fully represent all of the intricacies of the car in a racing competition. As a result, simulation results only represent an interpretation of the potential performance of the racing car. No guarantee or warrantee of performance in practice can be based on simulation results alone.

For the purposes of the challenge, the CFD analysis is aimed at providing an indicative performance of the racing car. Constraints of human and computer resources are driving the CFD analysis towards the selection of features based on robustness more than accuracy. One of the purpose of the 2012 test run is to assess that CFD analysis can be reliably applied to the design submitted with limited user input and constraint on the vehicle design.

Thanks

The analysis presented here and for the KVRC are run on Sabalcore computers. Big Thanks to them.

Aims

Computational Fluid dynamics allow for the resolution of the airflow pattern around the racing car. Idealised assumptions such as a uniform air velocity profile (meaning there is no wake generated by a car in front) are used to define the simulation scenario.

For the KVRC, three scenarios are used:
  1. Scenario 1: Head on at speed of 180mph;
  2. Scenario 2: Head on at speed of 100mph;
  3. Scenario 3: 3 degree yaw at speed of 100mph.

The CFD results are post-processed to extract the following information for each scenario:

  • Overall drag forces;
  • Overall downforces;
  • Center of application of the downforce (aka Centre of Pressure - COP), in other words the distance between the front wheel axle and the point of application of the downforce (ie the point where the downforce would not generate moment).

This information is then input into Virtual Stopwatch from Competition Car Engineering to establish the lap time... It all sounds very simple, but there is a number of hurdles along the way as CFD is neither forgiving nor without its myriad of parameters and assumptions.

KVRC Showcar Results

The table below reports the CFD results for the KVRC Showcar (Nicholas McDowell's car):

  Drag (N)Downforce (N) COP (m)
 Scenario 1 - Head on, 180mph 5372.8N8286.6N  1.89m
 Scenario 2 - Head on, 100mph 1648.8N2480.2N 1.86m 
 Scenario 3 - 3 degree yaw, 100mph1627.7N 2408.8N 1.83m 

The lap time predicted by Virtual StopWatch for the Monaco circuit is: 1minutes and 17.32 seconds.


Lola B2/00 Sample Analysis

As part of the assessment of the CFD methodology, Nicholas proposed to run a CFD analysis on the Lola B2/00 car geometry from the SketchUp warehouse (model by Timmy - unrelated to KVRC, warehouse link here, or just start SketchUp go to the warehouse and search for Lola B2/00). The analysis was conducted for a head on scenario with a speed of 140mph using a setup identical to the one used for the KVRC Showcar. An archive with the setup and analysis result file in VTK format can be downloaded at here.

The pictures provide an overview of the setup, car geometry, and results. If you download the archived results, you will notice that the meshing algorithm has generated a mesh inside parts of the car - this is also visible on the results pictures on the front nose cone and side pods. This is associated with non-closed geometry. The algorithm is sufficiently robust to handle these geometry problems - hopefully with limited impact on the results.

It is our intent to provide one of CFD analysis results for the above scenario to the participants along the other results - we would love to provide all three but it is putting a high burden on disk space storage. This is the opportunity for participants to have a look at their results, assess areas where performances can be improved (as well as give feedback on the results). The data file will be provided in VTK format, which can be read using ParaView (http://www.paraview.org/), an open source visualisation software.

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