Drag reduction in transonic shock-wave/boundary-layer interaction using porous medium: a computational study
TL;DR: In this paper, the effect of porosity on the normal-shock-wave/boundary-layer interaction at transonic speeds with a view toward application in aircraft wings is investigated.
Abstract: A computational study has been carried out to assess the effectiveness of a porous medium as a passive control device suitable for reducing the drag in a normal-shock-wave/boundary-layer interaction at transonic speeds with a view toward application in aircraft wings. Reduction in overall drag is achieved via recirculation inside the porous medium, which primarily weakens the shock structure and hence reduces the wave drag. The study has been carried out for a Mach 1.3 normal-shock-wave/boundary-layer interaction on a flat plate in the presence of a porous medium beneath the region of interaction. The computations are performed as steady-state RANS calculations using Menter’s SST $$k-\omega /k-\epsilon $$
model for turbulence closure. A parametric study that investigates the dependency of the effectiveness of control on dimensions of the cavity (length and depth), relative position of the cavity, and porosity of the medium has been carried out. It is observed that the change in overall drag is pronounced for parameters which result in significant changes to the size of the lambda-shock structure, such as the length of the cavity upstream of the inviscid shock location. Among the parameters investigated, porosity is seen to strongly affect the boundary-layer properties, with increase in porosity resulting in higher viscous drag.
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TL;DR: In this paper, a density-based coupled explicit algorithm, combined with a third-order MUSCL scheme and the Roe averaged flux difference splitting method, was used to solve the Navier-Stokes equations and the realizable k-e turbulence model.
Abstract: This study is focused on the propagation behavior and attenuation characteristics of a planar incident shock wave when propagating through an array of perforated plates. Based on a density-based coupled explicit algorithm, combined with a third-order MUSCL scheme and the Roe averaged flux difference splitting method, the Navier–Stokes equations and the realizable k-e turbulence model equations describing the air flow are numerically solved. The evolution of the dynamic wave and ring vortex systems is effectively captured and analyzed. The influence of incident shock Mach number, perforated-plate porosity, and plate number on the propagation and attenuation of the shock wave was studied by using pressure- and entropy-based attenuation rates. The results indicate that the reflection, diffraction, transmission, and interference behaviors of the leading shock wave and the superimposed effects due to the trailing secondary shock wave are the main reasons that cause the intensity of the leading shock wave to experience a complex process consisting of attenuation, local enhancement, attenuation, enhancement, and attenuation. The reflected shock interactions with transmitted shock induced ring vortices and jets lead to the deformation and local intensification of the shock wave. The formation of nearly steady jets following the array of perforated plates is attributed to the generation of an oscillation chamber for the inside dynamic wave system between two perforated plates. The vorticity diffusion, merging and splitting of vortex cores dissipate the wave energy. Furthermore, the leading transmitted shock wave attenuates more significantly whereas the reflected shock wave from the first plate of the array attenuates less significantly as the shock Mach number increases. The increase in the porosity weakens the suppression effects on the leading shock wave while increases the attenuation rate of the reflected shock wave. The first perforated plate in the array plays a major role in the attenuation of the shock wave.
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TL;DR: In this article , the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering are highlighted. But, although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions.
Abstract: Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application.
3 citations
TL;DR: In this article , the authors used wind tunnel experiments at Mach 2.87 to investigate the effect of passive suction through holes in a wall with a square protrusion on the wall.
Abstract: The unsteady three-dimensional separated flow on a wall induced by a square protrusion (approximately twice the local boundary layer thickness in width and height), and its control by means of passive suction through holes, is investigated using wind tunnel experiments at Mach $2.87$. The baseline flow without any control was characterized and compared against the cases with bleed. A bow-shaped separation line on the wall with a mid-span separation length of $5.57\delta$ from protrusion face was traced from oil-flow visualization. The averaged pressure distribution surveyed using static pressure ports placed on the wall has mapped plateau, high-pressure, and a low-pressure region in the separated flow, distinctive to three-dimensional interactions. Ten control configurations were tested with suction holes placed along mid-span in the different pressure zones. Significant spanwise `Mean Reduction in Separation Length' of up to $0.93\delta$ was observed from oil-flow visualization. A comparison of observations from various control configurations suggested that bleeding the flow from the high-pressure region could in general delay the separation and reduce the bubble size. Further, time-resolved schlieren visualizations have confirmed reduction in both `mid-span separation length' and `shock-intermittent-region' with the introduction of suction in high-pressure region. Fourier and Proper Orthogonal Decomposition analysis done on the schlieren data has confirmed the presence of low-frequency separation-shock oscillations at Strouhal Numbers of order $10^{-2}$, both with and without control. Furthermore, the amplitudes of separation-shock oscillations in the spectrum were reduced with the introduction of suction simultaneously from two holes placed in high and low-pressure regions.
2 citations
TL;DR: In this article , the authors investigate the effects of a heterogeneous impact zone on the fate of a witness specimen initially protected by a bicontinuous nanoporous gold (NPG) target.
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TL;DR: In this paper, two new two-equation eddy-viscosity turbulence models are presented, which combine different elements of existing models that are considered superior to their alternatives.
Abstract: Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-ω model of Wilcox in the inner region of the boundary layer and switches to the standard k-e model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity
15,459 citations
TL;DR: This work recognizes the need for additional dissipation in any higher-order Godunov method of this type, and introduces it in such a way so as not to degrade the quality of the results.
3,892 citations
TL;DR: In this article, a simple theory based on replacing the effect of the boundary layer with a slip velocity proportional to the exterior velocity gradient is proposed and shown to be in reasonable agreement with experimental results.
Abstract: Experiments giving the mass efflux of a Poiseuille flow over a naturally permeable block are reported. The efflux is greatly enhanced over the value it would have if the block were impermeable, indicating the presence of a boundary layer in the block. The velocity presumably changes across this layer from its (statistically average) Darcy value to some slip value immediately outside the permeable block. A simple theory based on replacing the effect of the boundary layer with a slip velocity proportional to the exterior velocity gradient is proposed and shown to be in reasonable agreement with experimental results.
2,898 citations
TL;DR: In this paper, a theoretical justification for an empirical boundary condition proposed by Beavers and Joseph is given for non-homogeneous porous medium, and the statistical approach is checked by using it to derive Einstein's law for the viscosity of dilute suspensions.
Abstract: A theoretical justification is given for an empirical boundary condition proposed by Beavers and Joseph [1]. The method consists of first using a statistical approach to extend Darcy's law to non homogeneous porous medium. The limiting case of a step function distribution of permeability and porosity is then examined by boundary layer techniques, and shown to give the required boundary condition. In an Appendix, the statistical approach is checked by using it to derive Einstein's law for the viscosity of dilute suspensions.
1,139 citations
TL;DR: In this article, the effective thermal conductivity (ke), permeability (K), and inertial coefficient (f) of high porosity metal foams were derived by considering a circular blob of metal at the intersection of two fibers.
998 citations