In this study, experimental tests and Computational Fluid Dynamics are used to investigate the aerodynamic performance of two types of track-based racing cars. After the literature study, where automotive aerodynamics is discussed in very general terms, the air flow beneath a Formula One Grand Prix Racing Car is investigated. This is achieved by fitting the under-tray of a 30% scale model of the Parmalat Forti Ford FGO 1-95 with surface-static pressure ports and testing the model in a rolling-road wind tunnel. By varying a number of model parameters, it is found that the wheels significantly alter the pressure distribution under the floor of the racing car at positions away from the centre-line. It is shown that the front or rear wheel sets are independently sufficient to induce the flow changes. The addition of the other set then only produces milder and more local changes. The numerical part of the floor investigation is aimed at reproducing the centre-line flow pattern by solving the full Reynolds-Average Navier-Stokes equations over a two-dimensional curvilinear grid of the isolated floor. Two algorithms, Roe's flux-difference splitting method and the commercial package, STAR-CD which employs the SIMPLE algorithm and a two-equation turbulence model, are used to solve the governing equations. It is found that although the correct trends are observed when two different ride heights are simulated, absolute correlation is inadequate despite the use of experimentally-controlled boundary conditions. The simulations are however used to demonstrate the saturation in downforce with increasing vehicle speed. In order to improve numerical accuracy, a second study was launched where the effect of including the centre-line profile of the complete vehicle is investigated. To reduce the amount of detail a 1/12th scale model of a generic BMW Touring Car is used. Experimental data in the form of centre-line surface-static pressure coefficients are used for numerical correlation. The data is obtained by testing the three-dimensional model in a wind tunnel fitted with a stationary-road raised-platform floor. To establish continuity, the experimental data is used to show the similarities between the pressure distribution on the centre line of the open-wheel and the closed-wheel racing car. The effect of a rear-mounted aerodynamic device on the downforce is also discussed. The numerical investigation using the SIMPLE algorithm of STAR-CD and three high Reynolds-Number turbulence models, is based on the centre-line profile of the experimental model. It is seen that although qualitative correlation exists in areas around the car, quantitative agreement is less positive. Discrepancies are found to be most significant under the floor. It is shown that the influence of the three dimensional flow field on the experimental results are unlikely to cause satisfactory correlation. It is suggested that, in order to improve correlation, a new investigation is launched aimed at refining the numerical model. An outline for the new study is presented and includes simulations indicating the dependence of the computational solution on the density of the grid and on the user-definable turbulence parameters. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 1999. / Mechanical and Aeronautical Engineering / unrestricted

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, September 2016 / The work in this dissertation presents the analysis of developing a novel means of flight trajectory alteration of a civil aircraft. Piezoelectric actuators have been advancing in the aerospace industry with uses in structural, vibrational and sensing applications. However, they have not been considered as a primary control method like an elevator, aileron and rudder. The analysis performed in this research involved developing an actuation model which is designed such that various changes in flight trajectory are brought about. The analysis began by building a base rigid aircraft model, where other analyses were appended to. The rigid aircraft model was developed using the aerodynamics of both Roskam (2001) and DATCOM. The DATCOM model was found to compensate for additional aircraft positions outside the flight envelope, whereas Roskam (2001) did not adequately provide the aerodynamics for when the aircraft would experience stall conditions, for example. The research then lead into developing the piezoelectric actuation model. This involved utilizing piezoelectric actuators on the wing of the aircraft, which was set to create vertical and twisting deformations, without altering the wing’s camber. Two novel methods of actuation are discussed. A wing - twist mode which consisted of three types of actuation, viz. linear twist, inverse linear twist, and linear twist symmetric. The second was the bending mode which altered the aircraft’s dihedral, and consisted of two types of actuation, viz. linear bending and linear bending symmetric. Effects of these two modes on the aerodynamics were depicted. Added to the overall model was the analysis of elastic aerodynamic effects. This was conducted by performing vibrational analysis on the individual components of the aircraft, viz. wing, horizontal tail and vertical tail. The results found that the elastic aerodynamic effects on the rigid model were significant only in lift. The rest were not significant because of the high frequency of the beams under consideration. Conclusively, the novel actuation methodology developed in this research yielded results demonstrating the viability of it being used above conventional methods such as elevator, rudder and ailerons. This was found by noting that various trajectory alterations were perceived without input from the conventional actuation methods. Increase in the rotational motions, as well as the translational motion was found, but did not cause any dynamic instabilities in the aircraft model. Thus, the actuation model was seen to operate well above the conventional methods, and situation specific uses were described for the actuation modes. These include uses in take-off and landing, cruise optimization and coordinated turns. / MT2017

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Supersonic channel airfoil design techniques have been shown to significantly reduce drag in high-speed flows over diamond shaped airfoils by Ruffin and colleagues. The effect of applying these techniques to a NACA 66-206 airfoil is presented. The design domain entails channel heights of 8-16.6% thickness-to-chord and speeds from Mach 1.5-3.0. Numerical simulations show an increase in the lift-to-drag ratio for airfoils at Mach 2.5 at a 35,000-ft altitude with a 12% channel height geometry showing a benefit of 17.2% at 6-deg angle of attack and a sharp channel leading edge. Wave drag is significantly reduced while viscous forces are slightly increased because of greater wetted area. Lift forces compared to clean airfoil solutions were also decreased, due mainly to the reduction in the length of the lifting surfaces. A tensile yield failure structural analysis of a typical beam found an 11.4% channel height could be implemented over 50% of the span between two typical ribs. A three dimensional wing was designed with the determined slot geometry and two dimensional flow analyses. An overall increase in L/D of 9% was realized at Mach 2.5 at a 35,000-ft altitude and 6-deg angle of attack.

This paper seeks to explore the effects of an active drag control method known as distributed forcing on a 3D bluff body with a blunt base. The 9.5 x 15.25 x 3 inch aluminum model constructed for this experiment has an elliptically shaped nose and rectangular aft section. The model is fitted with four, 12 Volt fans, forcing the freestream air into and out of 1 mm thick slots on the upper and lower trailing edges. The forcing is steady in time, held at a constant forcing velocity though all Reynolds numbers, but varies roughly sinusoidally in the spanwise direction across the model. Testing was conducted at Reynolds numbers of 50,000, 100,000 and 150,000 at California Polytechnic State University, San Luis Obispo in the Aerospace Engineering Department’s subsonic 3’ by 4’ wind tunnel. Effectiveness of the distributed forcing method was evaluated by measuring the base pressure on the model using a Scanivalve system. By measuring multiple static pressure ports, it was found that base pressure increased by 15.3% and 4.2% at Reynolds numbers of 50,000 and 100,000 respectively, and showed a decrease of 2.7% at a Reynolds number of 150,000. Total drag on the model was also measured using a sting balance mount fitted with strain gauges. This test showed a drag reduction of 15.8% and 5.5% for Reynolds numbers of 50,000 and 100,000 respectively, and an increase in drag of 2.0% at Reynolds number of 150,000, when omitting external power required to run the forcing assembly. The forcing assembly was shown to require nearly 12 times the power to operate than it saves in drag reduction at Reynolds number of 50,000. In addition, a thermal anemometry measurement of streamwise velocity of the near wake behind the bluff body was conducted to qualitatively assess the attenuation of the vortex street behind the model. Distributed forcing shows that as the freestream velocity is increased as compared to the forcing velocity, the change in energy spectral density is lessened, and as such, the largest attenuation in vortex shedding is at Reynolds number of 50,000 while nearly no change is seen at the Reynolds number of 150,000.

The Goldschmied Propulsor concept combines boundary layer suction and boundary layer ingestion to improve propulsive efficiency and reduce drag on an axisymmetric body. This investigation of a Goldschmied Propulsor aimed to determine influential characteristics of the suction slot geometry to aid in better slot geometry design and to decrease the suction flow requirements for maintaining attached flow over the entire model surface. The Propulsor model was 38.5 inches in length with a max diameter of 13.5 inches. Three suction slot geometries were investigated with the addition of aluminum cusps to the slot entrance. The cusps varied in the distance they protruded into the incoming suction flow and in the angle they took from the lip into the suction slot. Wind tunnel testing was completed in the Cal Poly 3ft x 4ft test section of the draw-down tunnel at a Reynolds Number of 2.3x106. Results show that of the three cusp geometries, the smallest Cusp A protruding only 0.05 inches into the suction flow, produced the greatest reductions in pressure drag and total axial force for the fan speeds tested. When compared to the no cusp condition, none of the three cusp geometries produced any significant improvement in total drag or in required suction flow rate.