Browsing by Subject "supersonic"
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Item Supersonic turbulent boundary layers with periodic mechanical non-equilibrium(Texas A&M University, 2007-04-25) Ekoto, Isaac WesleyPrevious studies have shown that favorable pressure gradients reduce the turbulence levels and length scales in supersonic flow. Wall roughness has been shown to reduce the large-scales in wall bounded flow. Based on these previous observations new questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface roughness and favorable pressure gradients are combined? To answer these questions and to enhance the current experimental database, an experimental analysis was performed to provide high fidelity documentation of the mean and turbulent flow properties along with surface and flow visualizations of a high-speed ( 2.86 M = ), high Reynolds number (Re 60,000 q ???? ) supersonic turbulent boundary layer distorted by curvature-induced favorable pressure gradients and large-scale ( 300 s k + ???? ) uniform surface roughness. Nine models were tested at three separate locations. Three pressure gradient models strengths (a nominally zero, a weak, and a strong favorable pressure gradient) and three roughness topologies (aerodynamically smooth, square, and diamond shaped roughness elements) were used. Highly resolved planar measurements of mean and fluctuating velocity components were accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized using pressure sensitive paint. Finally flow visualization was accomplished using schlieren photographs. Roughness topology had a significant effect on the boundary layer mean and turbulent properties due to shock boundary layer interactions. Favorable pressure gradients had the expected stabilizing effect on turbulent properties, but the improvements were less significant for models with surface roughness near the wall due to increased tendency towards flow separation. It was documented that proper roughness selection coupled with a sufficiently strong favorable pressure gradient produced regions of ??????negative?????? production in the transport of turbulent stress. This led to localized areas of significant turbulence stress reduction. With proper roughness selection and sufficient favorable pressure gradient strength, it is believed that localized relaminarization of the boundary layer is possible.Item The effects of diamond injector angles on flow structures at various Mach numbers(Texas A&M University, 2006-10-30) McLellan, Justin WalterNumerical simulations of a three dimensional diamond jet interaction flowfield at various diamond injector half angles into a supersonic crossflow were presented in this thesis. The numerical study was performed to improve the understanding of the flame holding potential by extending the numerical database envelop to include different injector half angles and examine the flow at Mach 2 and Mach 5. The configuration of a diamond injector shape was found to reduce the flow separation upstream, and produce an attached shock at the initial freestream interaction and the injection fluid has an increased field penetration as compared to circular injectors. The CFD studies were also aimed at providing additional information on the uses of multiple injectors for flow control. The numerical runs were performed with diamond injectors at half angles of 10???? and 20???? at a freestream Mach number of 5. The transverse counter-rotating pair of vortices found in the 15???? does not form within the 10???? and 20???? cases at freestream Mach number 5. The 10???? case had a barrel shock that became streamlined in the lateral direction. The 20???? barrel shock had a very large spanwise expansion and became streamlined in the transverse direction. In both cases the trailing edge of their barrel shocks did not form the flat ??????V?????? shape, as found in the baseline case. At Mach 2 the 10???? and 15???? cases both formed the flat ??????V?????? shape at the trailing edge of the barrel shocks, and formed the transverse counter rotating vortex pairs. The 10???? multiple injector case successfully showed the interaction shocks forming into a larger planer shock downstream of the injectors. The swept 15???? case produced interaction shocks that were too weak to properly form a planar shock downstream. This planar shock has potential for flow control. Depending on the angle of incidence of the injector fluid with the freestream flow and the half angle of the diamond injector, the planar shocks will form further upstream or downstream of the injector.