Numerical simulation of hypersonic flow around a sharp cone

A hypersonic viscous flow in the shock layer near sharp cones is considered. The profiles of density and velocity, the slopes of the shock wave, and the pressures and heat fluxes calculated on the basis of the full viscous shock layer equations are compared with available experimental and theoretical data.     

Control of the near-wake flow around a circular cylinder with electrohydrodynamic actuators

We analysed the modifications of the near wake of a circular cylinder (2,300< Re <58,000) when the flow was perturbed steadily using an electrohydrodynamic actuator. Two electrodes flush-mounted on the surface of the cylinder were excited with DC power supplies to create a plasma sheet contouring the body. The discharge produced an electric force and changed the physical properties in the fluid layers at close vicinity to the surface. This plasma sheet diminished the base pressure, modified the size of the mean recirculation region and produced an increase in the shear stresses of the layers bounding the contour of this region.     

Suppression of vortex shedding for flow around a circular cylinder using optimal control

Adjoint formulation is employed for the optimal control of flow around a rotating cylinder, governed by the unsteady Navier–Stokes equations. The main objective consists of suppressing Karman vortex shedding in the wake of the cylinder by controlling the angular velocity of the rotating body, which can be constant in time or time‐dependent. Since the numerical control problem is ill‐posed, regularization is employed. An empirical logarithmic law relating the regularization coefficient to the Reynolds number was derived for 60?Re?140. Optimal values of the angular velocity of the cylinder are obtained for Reynolds numbers ranging from Re=60 to Re=1000. The results obtained by the computational optimal control method agree with previously obtained experimental and numerical observations. A significant reduction of the amplitude of the variation of the drag coefficient is obtained for the optimized values of the rotation rate. Copyright © 2002 John Wiley & Sons, Ltd.     

Investigation of the supersonic flow around a pointed elliptical cone at an angle of attack

The picture of ideal gas flow around cones at zero and low angles of attack has been well studied by using approximate methods [1], and results for high angles of attack have been obtained mainly numerically [2–7]. At high angles of attack it is sensible to examine inviscid flow only up to some generator on the downwind side of the cone at which boundary-layer separation occurs. Hence, the domain where the flow can be considered inviscid yields the main contribution to the magnitude of the aerodynamic forces and the heat fluxes [5, 9]. A picture of the supersonic flow around a pointed elliptical cone is obtained in this paper by the numerical solution of the gasdynamics equations. The whole flow domain is computed at low angles of attack while the solution at high angles is obtained in a domain bounded by some surface of three-dimensional type [10]. The dependence of the flow parameters on the angle of attack is studied when the shock is attached to the cone apex. In contrast to a circular cone, at low angles of attack two spreading lines occur on the surface of an elliptical cone, to which the maximum pressure corresponds. As the angle of attack increases, these lines come together and merge at a certain time. At high angles of attack the flow picture is analogous to a circular cone with a pressure maximum in the plane of symmetry.     

Visualization of flow and vortex structure around a swimming loach by dynamic stereoscopic PIV

Loach has a unique swimming style of bending the whole body and staying at the bottom of water. We studied the three-dimensional flow field around and behind the loach using stereoscopic-PIV. We captured flow fields in horizontal and vertical plane, and it seems loach leaves vortex tube arches. From the analysis of body motion and flow field, we propose flow structure with vortex tube arches connected along the loach body. After being released, they are separated and flow away and dissipate. This research article was submitted for the special issue on Animal locomotion: The hydrodynamics of swimming (Vol. 43, No. 5).     

Reynolds number dependence of vortex patterns in accelerated flow around airfoils

Reynolds number dependence of vortical patterns visualized by smoke technique in accelerating flow behind airfoils is documented in photographic sequences at angles of attack 20° and 60°. At low Reynolds numbers the vortical pattern development is quite simple. With increasing Reynolds numbers these patterns become increasingly complex, and onset of turbulence occurs early and generates large scale turbulent vortex patterns.     

Effect of span length and temperature on the 3-D confined flow around a vortex promoter

This article presents a numerical study on the influence of span length and wall temperature on the 3-D flow pattern around a square section vortex promoter located inside a micro-channel in the low Reynolds number regime. The first objective of the work is to quantify the critical Reynolds number that defines the onset of vortex shedding and to identify the different regimes that appear as a function of the channel aspect ratio (span to height ratio). We found that the critical Reynolds number for the onset of the Karman street regime increases as the aspect ratio decreases. In particular, for the aspect ratio of 1/2 the critical Reynolds number is nearly six times the critical Reynolds number of the 2-D problem. An intermediate oscillating regime between the steady and the Karman street solutions was also found to exist within a rather wide range of Reynolds numbers for small channel aspect ratios. The second objective was to investigate the influence of the vortex promoter wall temperature on both vortex shedding and flow pattern. This has practical engineering implications because the working fluid considered in the article is water that has a viscosity that depends significantly on temperature and promotes a strong coupling between the momentum and energy equations that influences the system behaviour. Results indicate that high surface temperature on the prism promotes the onset of the Karman street, suggesting design guidelines for micro-channel based heat sinks that make use of vortex promoters.     

Effect of span length and temperature on the 3-D confined flow around a vortex promoter

This article presents a numerical study on the influence of span length and wall temperature on the 3-D flow pattern around a square section vortex promoter located inside a micro-channel in the low Reynolds number regime. The first objective of the work is to quantify the critical Reynolds number that defines the onset of vortex shedding and to identify the different regimes that appear as a function of the channel aspect ratio (span to height ratio). We found that the critical Reynolds number for the onset of the Karman street regime increases as the aspect ratio decreases. In particular, for the aspect ratio of 1/2 the critical Reynolds number is nearly six times the critical Reynolds number of the 2-D problem. An intermediate oscillating regime between the steady and the Karman street solutions was also found to exist within a rather wide range of Reynolds numbers for small channel aspect ratios. The second objective was to investigate the influence of the vortex promoter wall temperature on both vortex shedding and flow pattern. This has practical engineering implications because the working fluid considered in the article is water that has a viscosity that depends significantly on temperature and promotes a strong coupling between the momentum and energy equations that influences the system behaviour. Results indicate that high surface temperature on the prism promotes the onset of the Karman street, suggesting design guidelines for micro-channel based heat sinks that make use of vortex promoters.     

Application of a vortex lattice numerical model in the calculation of inviscid incompressible flow around delta wings

The flow over a flat plate delta wing at incidence and in sideslip is studied using vortex lattice models based on streamwise penelling. For the attached flow problem the effect of sideslip is simulated by modifying the standard vortex lattice model for zero sideslip by aligning the trailing vortices aft of the wing along the resultant flow direction. For the separated flow problem a non-linear vortex lattice model is developed for both zero and non-zero sideslip angles in which the shape and position of the leading edge separation vortices are calculated by an iterative procedure starting from an assumed initial shape. The theoretical values are compared with available theoretical and experimental results.     

Investigation of the velocity fluctuation spectrum of a vortex flow of vibrationally excited molecular gas in a glow discharge

The flow velocity fluctuations in a gas laser are measured under non-self-maintained glow discharge conditions. Spectra of the pulsating velocity signal on the frequency interval up to 2 kHz and the time dependence of the signal under glow and neutral flow conditions for pure nitrogen, a mixture of nitrogen and helium, and a trial CO₂-N₂-He mixture are obtained. Deformation (due to the action of the discharge) of the spectra of the transverse velocity component in the wake of a right circular cylinder is observed. In order to analyze the data obtained a model of the dynamic response of the pulsating velocity is constructed and a model of the Kármán vortex street behind a body is generalized with allowance for variations of the oscillation phase in the street. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 81–91, March–April, 2000. The work was carried out with partial financial support from the Russian Foundation for Basic Research (projects Nos. 96-01-00372 and 99-01-01199).     

A study of heat-transfer processes in a supersonic flow around a spherically blunted cone with allowance for injection of a gas-cooler

The heat- and mass-transfer processes of a spherically blunted cone and a supersonic air flow are identified by the methods of solving direct and inverse problems with allowance for the heat flow along the contour and the injection of a gas-cooler. The ranges of applicability of the standard one-dimensional approaches and the method of a thin wall for recovering heat fluxes directed toward the body in flow are shown in the entire time period considered. State University of Tomsk, Tomsk 634050. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 5, pp. 123–132, September–October, 1999.     

Cylindrical shock waves generated by a spark discharge and their interaction with the shock waves from a pulsed induction discharge

An experimental investigation of a spark discharge in argon is described. The existence of a shock wave and a following thermal wave is demonstrated. The experimental law of propagation of the thermal wave front is obtained. The effect of the discharge parameters on the dynamics of both waves is studied. The interaction between the cylindrical shock waves generated by a pulsed induction discharge and the shock waves formed in a spark discharge is considered. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 166–170, January–February, 1994.     

Numerical analysis of unsteady cavitating turbulent flow and shedding horse-shoe vortex structure around a twisted hydrofoil

Cavitating turbulent flow around hydrofoils was simulated using the Partially-Averaged Navier–Stokes (PANS) method and a mass transfer cavitation model with the maximum density ratio (ρ_l/ρ_v,clip) effect between the liquid and the vapor. The predicted cavity length and thickness of stable cavities as well as the pressure distribution along the suction surface of a NACA66(MOD) hydrofoil compare well with experimental data when using the actual maximum density ratio (ρ_l/ρ_v,clip = 43391) at room temperature. The unsteady cavitation patterns and their evolution around a Delft twisted hydrofoil were then simulated. The numerical results indicate that the cavity volume fluctuates dramatically as the cavitating flow develops with cavity growth, destabilization, and collapse. The predicted three dimensional cavity structures due to the variation of attack angle in the span-wise direction and the shedding cycle as well as its frequency agree fairly well with experimental observations. The distinct side-lobes of the attached cavity and the shedding U-shaped horse-shoe vortex are well captured. Furthermore, it is shown that the shedding horse-shoe vortex includes a primary U-shaped vapor cloud and two secondary U-shaped vapor clouds originating from the primary shedding at the cavity center and the secondary shedding at both cavity sides. The primary shedding is related to the collision of a radially-diverging re-entrant jet and the attached cavity surface, while the secondary shedding is due to the collision of side-entrant jets and the radially-diverging re-entrant jet. The local flow fields show that the interaction between the circulating flow and the shedding vapor cloud may be the main mechanism producing the cavitating horse-shoe vortex. Two side views described by iso-surfaces of the vapor volume fraction for a 10% vapor volume, and a non-dimensional Q-criterion equal to 200 are used to illustrate the formation, roll-up and transport of the shedding horse-shoe vortex. The predicted height of the shedding horse-shoe vortex increases as the vortex moves downstream. It is shown that the shape of the horse-shoe vortex for the non-dimensional Q-criterion is more complicated than that of the 10% vapor fraction iso-surface and is more consistent with the experiments. Further, though the time-averaged lift coefficient predicted by the PANS calculation is about 12% lower than the experimental value, it is better than other predictions based on RANS solvers.