![]() Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Satisfactory designs are usually obtained with 20–40 design cycles.read more read lessĪbstract: The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. The power of the method is illustrated by designs of wings and wing–body combinations for long range transport aircraft. The cost is kept low by using multigrid techniques, in conjunction with preconditioning to accelerate the convergence of the solutions. Each design cycle requires the numerical solution of both the flow and the adjoint equations, leading to a computational cost roughly equal to the cost of two flow solutions. This process is repeated until an optimum solution is approached. The Frechet derivative of the cost function is determined via the solution of an adjoint partial differential equation, and the boundary shape is then modified in a direction of descent. ![]() The theory is applied to a system defined by the partial differential equations of the flow, with the boundary shape acting as the control. It extends previous work on optimization for inviscid flow. The depleted stresses reduce the skin friction, which can lead to premature separation.read more read lessĪbstract: This paper describes the formulation of optimization techniques based on control theory for aerodynamic shape design in viscous compressible flow, modeled by the Navier–Stokes equations. LES content may be lacking because the resolution is not fine enough to fully support it, and/or because of delays in its generation by instabilities. The grid spacing is then fine enough for the DES length scale to follow the LES branch (and therefore lower the eddy viscosity below the RANS level), but resolved Reynolds stresses deriving from velocity fluctuations (“LES content”) have not replaced the modeled Reynolds stresses. This behavior begins when the grid spacing parallel to the wall Δ∥ becomes less than the boundary-layer thickness δ, either through grid refinement or boundary-layer thickening. ![]() However its initial formulation, denoted DES97 from here on, can exhibit an incorrect behavior in thick boundary layers and shallow separation regions. Different techniques of simulating turbulent flows - direct numerical simulation, large-eddy simulation or solution of the Reynolds-averaged Navier-Stokes equations using different turbulence models are presented and it is explained which technique is appropriate for which type of flow.Abstract: Detached-eddy simulation (DES) is well understood in thin boundary layers, with the turbulence model in its Reynolds-averaged Navier–Stokes (RANS) mode and flattened grid cells, and in regions of massive separation, with the turbulence model in its large-eddy simulation (LES) mode and grid cells close to isotropic. Both the drag crises on a cylinder at the critical Reynolds number and the Magnus effect on a rotating cylinder are described. The flow separation and recirculation can have many different forms, leading to vortex shedding (the von Karman vortex street), transition to turbulence in the wake, in shear layers, or in boundary layers on cylinder surface. Depending on the Reynolds number, the flow may be creeping, steady or unsteady laminar, or turbulent. Circular cylinder is a generic representation of a slender body exposed to a cross-flow such situations are found in many practical applications. In Week 4, we'll explore flows around a circular cylinder at Reynolds numbers between 5 and 5 million are studied.
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