Race Car Vehicle Dynamics

Assessment of hybrid RANS-LES formulations for flow simulation around the Ahmed body

On the two flow states in the wake of a hatchback Ahmed body

Effect of turbine nacelle and tower on the near wake of a utility-scale wind turbine

https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1144&context=aero_fac

The aerodynamic effects on a cornering Ahmed body

The aerodynamic performance of inverted wings on racing-car configurations is most critical when cornering; however, current wind tunnel techniques are generally limited to the straight-line condition. The true cornering condition introduces complexity because of the curvature of the freestream flow. This results in an increase in the tangential velocity with increasing distance from the instantaneous center of rotation and causes the front wing to be placed at a yaw angle. Numerical simulations were used to consider an 80% scale front wing when steady-state cornering with radii ranging from 60m to 7.5m, and yaw angles ranging from 1.25° to 10°. The changes to the pressure distribution near the endplates caused the wake structure to become highly asymmetric. Both the primary longitudinal vortices and the secondary longitudinal vortices differed in strength, and the vortex core positions shifted in the vertical direction and the spanwise direction. The change in the position became more substantial further downstream as the structures tended toward the freestream direction. The effects on the wing surface pressure distribution resulted in the introduction of yawing and rolling moments, as well as a side force and an increase in drag. The results demonstrate the importance of evaluating the cornering condition if that is where a good performance is most sought after.

/pdf/the-influence-of-cornering-on-the-vortical-wake-structures-1p55j005er.pdf

The influence of cornering on the vortical wake structures of an inverted wing

A numerical investigation has been conducted into the influence of flow compressibility effects around an open-wheeled racing car. A geometry was created to comply with 2012 F1 regulations. Incompressible and compressible CFD simulations were compared – firstly with models which maintained Reynolds number as Mach number increased, and secondly allowing Mach number and Reynolds number to increase together as they would on track. Results demonstrated significant changes to predicted aerodynamic performance even below Mach 0·15. While the full car coefficients differed by a few percent, individual components (particularly the rear wheels and the floor/diffuser area) showed discrepancies of over 10% at higher Mach numbers when compressible and incompressible predictions were compared. Components in close ground proximity were most affected due to the ground effect. The additional computational expense required for the more physically-realistic compressible simulations would therefore be an additional consideration when seeking to obtain maximum accuracy even at low freestream Mach numbers.

/pdf/flow-compressibility-effects-around-an-open-wheel-racing-car-4urqjflgas.pdf

Flow compressibility effects around an open-wheel racing car

When a vehicle travels through a corner it can experience a significant change in aerodynamic performance due to the curved path of its motion. The yaw angle of the flow will vary along its length and the relative velocity of the flow will increase with distance from the central axis of its rotation. Aerodynamic analysis of vehicles in the cornering condition is an important design parameter, particularly in motorsport. Most racing-cars are designed to produce downforce that will compromise straight-line speed to allow large gains to be made in the corners. Despite the cornering condition being important, aerodynamicists are restricted in their ability to replicate the condition experimentally. Whirling arms, rotary rigs, curved test sections and bent wind tunnel models are experimental techniques capable of replicating some aspects of the cornering condition, but are all compromised solutions. Numerical simulation is not limited in the same way and permits investigation into the condition. However, cornering introduces significant change to the flowfield and this must be accommodated for in several ways. Boundary conditions are required to be adapted to allow for the curved flow occurring within a non-inertial reference frame. In addition, drag begins to act in a curved path and variation in Re occurs within the domain. Results highlight the importance of using correct analysis techniques when evaluating aerodynamic performance for cornering vehicles.

/pdf/techniques-for-aerodynamic-analysis-of-cornering-vehicles-4di9slvfhy.pdf

Techniques for Aerodynamic Analysis of Cornering Vehicles

For racing car configurations an inverted wing produces negative lift that allows increased levels of acceleration to be maintained through corners. Routine aerodynamic analysis, however, will typically be in the straight-line condition. A numerical analysis of the inverted T026 wing geometry through the curved path of a constant radius corner was conducted. The asymmetrical properties of the oncoming flow resulted in the introduction of a rolling and yawing moment along the span, as well as side-force. Yaw angle, flow curvature and a velocity gradient resulted in changes to the pressure distribution over the wing surface. Primary vortex behaviour was observed to differ significantly in both direction and structure.

/pdf/the-aerodynamics-of-a-cornering-inverted-wing-in-ground-1i5r0trxyp.pdf

James Keogh

Papers

The aerodynamic effects on a cornering Ahmed body

The influence of cornering on the vortical wake structures of an inverted wing

Flow compressibility effects around an open-wheel racing car

Techniques for Aerodynamic Analysis of Cornering Vehicles

The Aerodynamics of a Cornering Inverted Wing in Ground Effect