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No description available.

No description available.

Numerical investigations of laminar shock-wave/boundary-layer interactions (SWBLIs) in hypersonic flow have been carried out at M∞ = 6.85 and M∞ ≈ 8, with unit Reynolds numbers ranging from 2.0 x 106 m- l to 7.60 x 106 m- l. This thesis deals with a simplified 2-D geometric configuration to simulate SWBLIs on vehicle surfaces or engine intakes, i.e. the interaction of an oblique shock (produced by a wedge) impinging on an incoming laminar boundary-layer on an isothermal flat plate. The numerical simulations were performed with weak/moderate to strong shock. The results were compared with available theoretical and experimental results. Limited experimental work at M∞ = 6.85 for obtaining qualitative data were performed to provide the location of separation and re-attachment points using surface oil flow. Schlieren photographs were taken to provide the general flow features. A comprehensive analysis was performed on the 2-D numerical results with various Mach numbers, Reynolds numbers and shock strengths, to verify whether numerical solutions were able to confirm the established trends for the laminar free-interaction concept. An analysis was also performed using a well-established power-law relationship of pressure and heat flux in the region of interactions. An unstable first oblique mode disturbance was imposed with the strongest wedge angle, 9°, at M∞ = 6.85 and unit Reynolds number 2.45 x 106 m- l to determine the boundary-layer stability and its propensity to undergo transition in the linear regime. Several unsteady 3-D simulations were performed with varied parameters. Streamwise vortices were generated in all cases especially downstream of maximum separation bubble height. However, as the amplifications of the disturbance were quite small, transition was found to be unlikely at these conditions

The three-dimensional numerical simulation of a Mach 6.7 perfect gas, with a unit Reynolds number of 7.6 x 106m-1, over several configurations of a blunt-fin attached to a flat plate are carried out. The resulting interference flowfield is reported in this thesis. The laminar Navier-Stokes code developed by Narvarro-Martinez [47] has been modified to solve any general three-dimensional problem, and the complete Navier-Stokes equations. The numerical scheme is operator split, allowing independent numerical schemes to be used on each of the individual contributions to the Navier-Stokes, which can be combined later to advance the entire solution in time. The inviscid part uses a first order Godunov method with a HLLC approximate Riemann solver; second order accuracy is achieved through the MUSCL approach. The viscous contribution is modeled by a centered difference scheme. An iterative matrix solver is used to advance the implicit solution in time. To handle large three-dimensional grids, the code is implicit and run on a parallel computer cluster. The three-dimensional results from the various blunt-fins simulated show a complex rich three-dimensional structure, with several horseshoe vortices formed within the separated flow. Extremely large heat transfer rates have been measured along the path of these vortices on the plate surface, and on the leading edge of the unswept blunt-fin. In particular cases heat transfer rates as high as (h/hu)60 were measured for the 5mm diameter fin. The 5mm fin results show remarkable similarity to the experimental results obtained by Schuricht [53]. The results obtained using a swept fin, and a fin of doubled fin diameter also show good agreement with the trends observed by Schuricht and others for a laminar interaction.

Unsteady flows occur in many applications of engineering interest. One category of unsteady flows occur as self-sustaining oscillatory fluid motion, such as the flow over rectangular cavities. There has been a significant amount of research performed on this topic over the years, both experimentally and numerically. The unsteady flow over rectangular cavities is the case study in this research. In this work, a generic numerical solver is developed and written to predict the near-field aerodynamics of unsteady fluid motions at low Mach numbers. High order numerical schemes are employed to this effect. The Detached Eddy Simulation (DES) method is considered for the turbulence modelling part. At the start of this project, the combination of high order Computational Aeroacoustics (CAA) numerical schemes, non-reflecting boundary conditions and DES constituted a state of the art approach to the simulation of unsteady compressible flow phenomena at low Mach numbers. In the numerical study of 2D cavities, a number of cases with different length-to depth (L/D) ratios were considered. Under the same flow conditions, the relation of the L/D to the radiated sound in the farfield is sought. It is found that the nature of the flow interaction with the downstream corner, which changes with L/D, dictates the directivity and amplitude of the sound field observed at a far distance from the source. To gain more insight into the topology of 3D cavity flows, an experimental study using non-intrusive measurement techniques is outlined. This explains the work performed on 3D cavities with different spanwise dimensions. A detailed flow visualisation of the meanflow patterns in various measurements planes describes the presence of strong 3D features. In particular, the symmetrical flow behaviours at relatively large width-to-depth (W/D) ratios of 3 and 2 are highlighted. This provides the justification to employ a symmetry condition in the 3D DES study. Therefore, the final case study is based on the numerical simulation of a 3D cavity geometry where only half of the cavity is simulated. The observations from the 2D simulations and the experimental work provided a basis of the expectations of this test case. Again, a correlation between the near-field aerodynamics and the farfield sound is sought. The 3D cavity showed (as in the 2D cases) a preferred directivity in the farfield.