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This study was performed to investigate aerodynamic characteristics of the 37.5% scaled­ down Green Raven MK18 airframe, to evaluate boundary corrections method, and to investigate on support interference. A wind tunnel test was originally planned on June 2021 at a Large­Low­Speed Wind Tunnel at University of Bristol; however, due to COVID­19 travel restrictions, the test has been postponed to November 2021. In or­der to supplement the work and data directly required for the test, computational fluid dynamics (CFD) investigations were performed in free air and in wind tunnel condi­tions, both with and without support interference, at a Reynolds number of 7E+05. The simulations utilized an incompressible Reynolds-­Averaged­-Navier.­Stokes equa­tion accompanied with k − ω SST for turbulent modelling. Corrections factors were obtained to compensate for wall interference, and results indicate a satisfactory agree­ment between free ­air and wind­ tunnel corrected data for wall interference. The sup­ port structure interferes with the aerodynamic loads produced by the model. Lift and drag decrease, and pitching moment increases compared to WT without support structure condition. / Denna studie utfördes för att undersöka aerodynamiska egenskaper hos det nedskalade Green Raven MK18­flygplanet för 37.5%, för att utvärdera gränskorrigeringsmetoden och för att undersöka stödinterferens. Ett vindtunneltest planerades ursprungligen i juni 2021 vid en stor­låghastighets vindtunnel vid University of Bristol. Men på grund av resebegränsningar för covid­19 har testet skjutits upp till november 2021. För att komplettera det arbete och de data som direkt krävs för testet, utfördes CFD under­ sökningar (Computational Fluid Dynamics) i fri luft och i vindtunnelförhållanden, både med och utan supportinterferens, med ett Reynolds­tal på 7E+05. Simuleringarna använde en inkompressibel Reynolds­Averaged­Navier­Stokes­ekvation tillsammans med k − ω SST för turbulent modellering. Korrigeringsfaktorer erhölls för att kom­ pensera för väggstörningar, och resultaten tyder på en tillfredsställande överensstäm­ melse mellan frilufts­ och vindtunnelkorrigerade data för väggstörningar. Stödstruk­ turen stör de aerodynamiska belastningar som modellen producerar. Lyft och drag minskar och stigningsmomentet ökar jämfört med WT utan stödstruktur.

The high complexity of vehicle front-end design, arising from considerations of aerodynamics, safety and styling, causes the airflow velocity profile at the radiator face to be highly distorted, leading to potentially reduced airflow volume for heat dissipation. A flow visualisation study showed that the bumper bar significantly influenced the cooling airflow, leading to three-dimensional vortices in its wake and generating an area of relatively low velocity across at least one third of the radiator core. Since repeatability and accuracy of on-road testing are prejudiced by weather conditions, wind-tunnel testing is often preferred to solve cooling airflow problems. However, there are constraints that limit the accuracy of reproducing on-road cooling performance from wind-tunnel simulations. These constraints included inability to simulate atmospheric conditions, limited tunnel test section sizes (blockage effects) and lack of ground effect simulations. The work presented in this thesis involved use of on-road and wind-tunnel tests to investigate the effects of most common constraints present in wind tunnels on accuracy of the simulations of engine cooling performance and radiator airflow profiles. To aid this investigation, an experimental technique for quantifying radiator airflow velocity distribution and an analytical model for predicting the heat dissipation rate of a radiator were developed. A four-hole dynamic pressure probe (TFI Cobra probe) was also used to document flow fields in proximity to a section of radiator core in a wind tunnel in order to investigate the effect of airflow maldistribution on radiator heat-transfer performance. In order to cope with the inability to simulate ambient temperature, the technique of Specific Dissipation (SD) was used, which had previously been shown to overcome this problem.

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