This page reports the analysis of the geometry analysis using One-Click CFD. The analysis setup uses the following input parameters:
- Speed: 44.7 m/s
The uploaded geometry has the following characteristics – please check these carefully. Mistakes can easily happen particularly when using unit-free format such as STL.
- Length (y axis direction): 5.00 m (Y from -1.00 to 4.00 m)
- Width (x axis direction): 2.01 m (X from -1.01 to 1.01 m)
- Height (z axis direction): 1.07 m (Z from -0.05 to 1.02 m)
- Frontal area – A: 1.80 m2. This is the projected area of the vehicle in the y axis direction.
The analysis was undertaken for the full car.
The drag and downforce performance predicted by the simulation are:
- Total drag: 2030.29 N
- Front wing(s) drag: 285.34 N
- Rear wing(s) drag: 326.12 N
- Drag area – Cd.A: 1.69 m2
- Total Downforce: -4666.32 N
- Front wing(s) downforce: -576.09 N
- Rear wing(s) downforce: -1497.37 N
- Downforce coefficient – Cl: -2.16
- Downforce area – Cl.A: -3.89 m2
- CoP of downforce: 1.491 m along streamwise (Y) direction from Y = 0.00 m.
- KVRC Only: Corrected CoP of downforce: 1.570 m along streamwise (Y) direction from Y = 0.00 m.
The pressure at intake and exhaust are:
- Engine intake, Area: 0.021m2 – Compliant
- Surface integral of pressure: 12.51 Pa.m2
- Engine exhaust, Area: 0.010m2 – Compliant
- Surface integral of pressure: -7.51 Pa.m2
- Cooling intake, Area: 0.399m2 – Compliant
- Cooling exhaust, Area: 0.400m2 – Compliant
- Differential of surface integral of pressure: -343.98 Pa.m2
Drag coefficient – Cd: 0.94
The CFD simulation is run to steady-state, ie the solution that would be reached if all the parameters remain constant for a long time. As the simulation gets close to the steady-state result, it is said that the simulation converges.
When doing CFD simulation in steady-state, one should check the convergence of the simulation. It is shown on this page by the following:
Residuals: This is a measure of the convergence of the numerical solver and equations. The residuals are a measure of the rate of change of the flow variables (air speed, turbulence, etc). The lower the residuals are, the less change there is in the flow variables, in other the more converged the solution is.
Time evolution of drag, downforce and center of pressure: While the residuals provide a measure of the convergence of the numerical solver, it is good practice to confirm convergence of physical metrics. In One-Click CFD, this corresponds to confirming that drag, downforce and center of pressure are flattening to a value or showing small oscillation around an asymptotic value. If the graph does not show convergence to an asymptotic value, the solution may not be converged and the results should be considered carefully.
CFD has long been referred to Color Fluid Dynamics, in relation to the pretty pictures that can be generated using this approach. These pretty pictures can not only be used to show off to your colleagues, manager, and clients (or competitors), but also to understand how the air is travelling around the car. This can be used to investigate questions such as how effective is the rear diffuser, or is the airflow around the rear wing affected by airflow around the body.
There are many forms of visualisation available. This webpage only shows the pressure distribution on the vehicle surface. Alongside this webpage are the simulation results that you can load in ParaView for further visualisation.
Useful visualisation includes:
Streamlines, which are particles with no weight that follows the air path. These streamlines can be used to visualise the air flow around the car.
Section cuts that shows the air velocity, static and total pressure at section through the computational domain.
Surface pressure shows the pressure at the surface of the body. As the drag and downforce are largely pressure induced, the pressure plot at the body surface can be used to identify area of high drag and downforce. Do keep in mind that the pressure generates a force normal to surface at which the pressure is applied, and that high positive and low negative pressure contribute to drag and downforce.
Wool tuft shows how the direction of the airflow at the surface of body. This can be used to visualise recirculation zones and changes in airflow patterns induced by wheel rotation for example.
Drag & Downforce Distribution
The drag and downforce distribution graphs shows the distribution of the drag and downforce surface alongside the car body. The distribution is obtained by integrating the pressure induced forces at sections of the car. The integral of the drag and downforce is equal to the total pressure induced drag and downforce.
These graphs excels at providing information on where high drag and downforce are generated. It can also be used to identify inbalance in downforce distribution, such as does the rear wings generates significantly higher downforce than the front wings.