Sammy Diasinos

Influence of wing span on the aerodynamics of wings in ground effect

A computational fluid dynamics study of the influence of wing span has been conducted for an inverted wing with endplates in ground effect. Aerodynamic coefficients were determined for different spans at different ground clearances, highlighting a trend for shorter spans to delay the onset of both separation and resulting loss of negative lift. The vortices at the wing endplates were not observed to change significantly in terms of strength and size; thus, at shorter spans, their influence over a larger percentage of the wing helped the flow stay attached and reduced the severity of the adverse pressure gradient which invokes separation at greater spans. Consequently, it was shown that, compared to a large-span wing, a wing with a shorter span may have a lower lift coefficient but can operate closer to the ground before performance is adversely affected.

The Influence of Cornering on the Vortical Wake Structures of an Inverted Wing

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 centre 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 60 m to 7.5 m, 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.

Synergistic integration of computational fluid dynamics and experimental fluid dynamics for ground effect aerodynamics studies

This article highlights the ‘synergistic’ use of experimental fluid dynamics (EFD) and computational fluid dynamics (CFD), where the two sets of simulations are performed concurrently and by the same researcher. In particular, examples from the area of ground effect aerodynamics are discussed, where the major facility used was also designed through a combination of CFD and EFD. Three examples are than outlined, to demonstrate the insight that can be obtained from the integration of CFD and EFD studies. The case studies are the study of dimple flow (to enhance aerodynamic performance), the analysis of a Formula-style front wing and wheel, and the study of compressible flow ground effect aerodynamics. In many instances, CFD has been used to not only provide complementary information to an experimental study, but to design the experiments. Laser-based, non-intrusive experimental techniques were used to provide an excellent complement to CFD. The large datasets found from both experimental and numerical simulations have required a new methodology to correlate the information; a new post-processing method has been developed, making use of the kriging and co-kriging estimators, to develop correlations between the often disparate data types.

Alignment technique for three-dimensional laser Doppler anemometry

Three-dimensional laser Doppler anemometry is a powerful, non-intrusive measurement technique. The high data rate point measurement allows direct quantification of turbulence quantities. However, for this type of study, a very high level of laser beam alignment is required; without good alignment only mean flow measurements are possible. We report here on an alignment procedure that is simple and cost-effective, yet results in much higher data rates than traditional, pinhole-based methods.

The Aerodynamics of a Cornering Inverted Wing in Ground Effect

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.

On the Interaction of a Racing Car Front Wing and Exposed Wheel

A numerical investigation of generic open-wheel racing car wing and wheel geometry has been conducted, using original sub-scale experimental data for validation. It was determined that there are three main interactions that may occur, identifiable by the path that the main and secondary wing vortices take around the wheel. Interaction ‘A’ occurs when the main and secondary wing vortices both travel outboard of the wheel; interaction ‘B’ is obtained when only the main wing vortex passes inboard of the wheel; while interaction ‘C’ sees both wing vortices travel inboard of the wheel. The different interactions are achieved when geometric changes to the wing affect the pressure distribution about the endplate, either by altering the magnitude of suction generated by the wing or by changing the locations of peak suction and vortices relative to the wheel’s stagnation regions. As a result, the influence that the wing and wheel have on each other – in comparison to the same bodies in isolation – varies, resulting in significant consequences for downforce and drag.

A new type of wind tunnel for the evaluation of curved motion

While aerodynamic analysis of the flow conditions during cornering can be an important design parameter for applications such as automobiles, vessels, and highly maneuverable aircraft, it can be difficult to simulate. This type of motion requires controlled and repeatable flow curvature, relative to the model. A new design to allow experimental testing for this condition has been developed, and by testing in a noninertial reference frame, flow curvature is achieved in the absence of a static pressure gradient. Initial results have demonstrated the ability of the concept to produce the correct flowfield and the new design offers potential for new experimental investigations that were previously unachievable.

Techniques for Aerodynamic Analysis of Cornering Vehicles

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.

Implications of compressibility effects for Reynolds-scaled testing of an inverted wing in ground effect

The influence of compressibility around an isolated inverted wing at a fixed Reynolds number was examined as relevant to the issue of wind tunnel scaling effects. Three-dimensional simulations were conducted for low ground clearances, at: full scale and a Mach number of 0.088, at 50% scale at Mach 0.176, and at 25% scale at Mach 0.352. As the scale was reduced, the increasing peak local Mach number between the wing and the ground resulted in a higher propensity of the flow to separate towards the trailing edge, and for incompressible or full-scale CFD to underestimate the lift and drag coefficients by an ever-increasing margin. The lower vortex path was less affected. The results suggest that compressible CFD of a scale experiment ought to be conducted at the same Reynolds number and Mach number as the tunnel test for the best possible correlation at free-stream Mach numbers beyond 0.15.

Numerical analysis of the effect of the change in the ride height on the aerodynamic front wing-wheel interactions of a racing car

An investigation into the influence of the ground clearance on the aerodynamic interactions between the inverted front wing and the wheel of a racing car was conducted using computational fluid dynamics. Height-to-chord ratios h/c from 0.075 to 0.27 were assessed for a single-element wing with a fixed angle of 4° and for two wing spans, one of which completely overlapped the wheel and the other which had its endplate coincident with the inside face of the wheel. With a narrower span, a lower peak downforce was achieved at a higher ground clearance owing to changes in the lower endplate vortex strength whereas, with a wider span, no downforce loss was observed, with decreasing clearance for those tested. This contrasted distinctly with the performance of the wing in isolation. The wheel lift was scarcely affected with decreasing wing ground clearance for the narrower span but decreased significantly for the wide-span wing at low ground clearances. The vortex paths changed considerably with the ground clearance, with a strong coupling to the wing span; a state in which the main vortex was destroyed in the contact patch of the wheel was identified.