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• W801047874 abstract "The difficulties regarding the control of high velocity flying vehicles in supersonic/hypersonic flight regime are still prevailing. Whether it is mixing enhancement,side force generation or aerodynamic steering, wall cooling or any otherfavourable method to control the flow, the resultant effects of different flow controltechniques on the associated flowfield demands careful experimental and numericalinvestigations. Traditional aerodynamic control surfaces are subjected tosevere flight conditions and loadings in different flight regimes resulting in impairedthe control effectiveness. Active flow control methods serve strong alternativeto achieve separation postponement, transition control, lift enhancement,mixing enhancement, drag reduction, turbulence modification and/or noise suppression,etc. This thesis deals with two main active flow control techniques;transverse jets at Mach 5 cross flow and energy deposition using arc discharge atMach 5 flow. The influence of roughness on the control effectiveness of transversejet interactions is also examined.The first objective of this thesis is to investigate experimentally the flowphysics of the sonic transverse jets at Mach 5 laminar cross flow both in timeaveraged and time resolved manner to provide reliable experimental data andbetter understanding at high Mach numbers. The parameters such as momentumflux ratio, incoming Reynolds number, type of the gas and the surface roughnessare studied. The size and structures of the upstream and downstream separationregions and jet penetration characteristics together with jet shear layer behaviourare examined. Moreover CFD simulations are conducted on a two dimensionalcase of Spaid and Zukoski and the numerical solver/procedure is validated. Thena three dimensional experimental case is simulated to provide greater understandingon the flow physics as well as to cross check measurements.As the main finding; jet interaction flow field can not be oversimplified andrepresented with only one parameter that is momentum flux ratio, J, as suggested by the literature; the incoming Reynolds number, type of injectant and roughnessare clearly affecting the interaction resulting in advantages or drawbacks for flowcontrol point of view.The second objective of this thesis is to investigate experimentally the dynamicsbetween the localised energy spot and the blunt body shock for dragreduction at Mach 5 flow. The localised energy spot is created firstly via steadyelectric arc struck between two electrodes using a small amount of energy andsecondly via pulsed laser focusing with a significant amount of energy. In caseof electric discharge, the effects of discharge are evaluated in comparison to nodischarge case with the electrodes. The unsteady wake/compression structuresare examined between the steadily deposited energy spot and the modified bowshock wave. And for the laser focussing unsteady interaction that is happeningin a short duration of time is investigated. The effect of the truncation, the distancebetween the electrodes and the model as well as the type and amount ofthe energy input on this phenomenon are examined. Moreover CFD simulationsare conducted on the baseline cases to cross check measurements together withtheoretical estimates.As the main finding; the effectiveness of the arc discharge is increasing withincreased truncation or the frontal area and when the arc to nose distance isthe shortest. However an important thing to note is that energy deposition atshorter distances might result higher stagnation point heating rates which aredetrimental. The test campaign clearly renders that the use of small amount ofonboard energy to create a local focused thermal spot in front of a vehicle is anefficient way of reducing drag." @default.
• W801047874 created "2016-06-24" @default.
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• W801047874 date "2011-12-13" @default.
• W801047874 modified "2023-09-29" @default.
• W801047874 title "Active flow control studies at Mach 5 : measurement and computation" @default.
• W801047874 hasPublicationYear "2011" @default.
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