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Freestream
About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.
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TL;DR: In this paper, a similar solution for the problem of hydrodynamic dispersion in mixed convection heat and mass transfer from vertical surface embedded in porous media has been presented, where the flow induced by the density variations is comparable with the freestream flow.
Abstract: Similarity solution for the problem of hydrodynamic dispersion in mixed convection heat and mass transfer from vertical surface embedded in porous media has been presented. The flow induced by the density variations is comparable with the freestream flow. The heat and mass transfer in the boundary layer region for aiding and opposing buoyancies in both aiding and opposing flows has been analyzed. The structure of the flow, temperature, and concentration fields in the Darcy and non-Darcy porous media are governed by complex interactions among the diffusion rate (Le) and buoyancy ratio (N) in addition to the flow driving parameter (Ra/Pe). The flow, temperature, and concentration fields are analyzed and the variation of heat and mass transfer coefficients with the governing parameters are presented
56 citations
TL;DR: In this paper, an experimental investigation was conducted to study and characterize the effects of injection angle on the breakup processes of turbulent liquid jets in a subsonic crosse flow of air, with water as the test liquid, the injection angle, freestream Mach number, and injection velocity were varied over a wide range.
Abstract: An experimental investigation was conducted to study and characterize the effects of injection angle on the breakup processes of turbulent liquid jets in a subsonic crosse ow of air. With water as the test liquid, the injection angle, freestream Mach number, and injection velocity were varied over a wide range to provide an extensive databaseofexperimentalresults.Pulsedshadowgraphphotographywasemployedtoascertaincolumntrajectories, column fracturelocations,and near-e eld spray characteristics.Resultsindicatethat column breakup behavior can be divided into two distinct regimes: aerodynamic and nonaerodynamic. Liquid column fracture locations were found to be governed by length scales, which depend on the corresponding breakup regime. For aerodynamic breakup, the column length scale was derived from thetimescale fortheanalogous process oftheaerodynamic secondary breakup ofadroplet.Fornonaerodynamicbreakup,thecolumnlengthscalewasderivedfromthetimescale for the breakup of a turbulent liquid jet issuing into a quiescent gas. A breakup regime parameter was dee ned to determine, based on jet operating conditions, the prevalent breakup regime and, therefore, the appropriate column length scale. Liquid column trajectories were correlated with an effective jet-to-freestream momentum e ux ratio and transverse injection angle by applying a force balance and momentum analysis. Comparisons between experimental data and analytical predictions are presented and show excellent agreement in most cases.
55 citations
TL;DR: In this paper, the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling is investigated using large-eddy simulations, where a cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re
Abstract: The present paper investigates the impact of the velocity and density ratio on the turbulent mixing process in gas turbine blade film cooling. A cooling fluid is injected from an inclined pipe at α=30° into a turbulent boundary layer profile at a freestream Reynolds number of Re ∞ = 400,000. This jet-in-a-crossflow (JICF) problem is investigated using large-eddy simulations (LES). The governing equations comprise the Navier–Stokes equations plus additional transport equations for several species to simulate a non-reacting gas mixture. A variation of the density ratio is simulated by the heat-mass transfer analogy, i.e., gases of different density are effused into an air crossflow at a constant temperature. An efficient large-eddy simulation method for low subsonic flows based on an implicit dual time-stepping scheme combined with low Mach number preconditioning is applied. The numerical results and experimental velocity data measured using two-component particle-image velocimetry (PIV) are in excellent agreement. The results show the dynamics of the flow field in the vicinity of the jet hole, i.e., the recirculation region and the inclination of the shear layers, to be mainly determined by the velocity ratio. However, evaluating the cooling efficiency downstream of the jet hole the mass flux ratio proves to be the dominant similarity parameter, i.e., the density ratio between the fluids and the velocity ratio have to be considered.
55 citations
22 Jun 2009
TL;DR: In this paper, the stability and receptivity of a 3D hypersonic boundary layer over a 7deg half-angle straight cone at an angle of attack of 6deg is numerically investigated at a freestream Mach number of 6.0 and a Reynolds number of 10.4x10(exp 6)/m.
Abstract: The stability and receptivity of a three-dimensional hypersonic boundary layer over a 7deg half-angle straight cone at an angle of attack of 6deg is numerically investigated at a freestream Mach number of 6.0 and a Reynolds number of 10.4x10(exp 6)/m. The generation and evolution of stationary crossflow vortices are also investigated by performing simulations with three-dimensional roughness elements located on the surface of the cone. The flow fields with and without the roughness elements are obtained by solving the full Navier- Stokes equations in cylindrical coordinates using a fifth-order accurate weighted essentially non-oscillatory (WENO) scheme for spatial discretization and a third-order total-variation-diminishing (TVD) Runge-Kutta scheme for temporal integration. Stability computations produced azimuthal wavenumbers in the range of m approx. 20-50 for the most amplified traveling disturbances and in the range of m approx.30-70 for the stationary disturbances. The frequency of the unstable second-mode ranges from 400 kHz to 900 kHz along the windward ray. The N-Factor computations predicted transition would occur more forward on the sides of the cone as compared to the transition fronts near the windward and the leeward rays. The simulations also show the crossflow vortices originating from the nose region propagate towards the leeward ray. No perturbations were observed toward the windward half of the cone.
55 citations
01 Jan 2005
TL;DR: In this article, particle image velocimetry (PIV) measurements have been performed over the suction surface of a low Reynolds number airfoil in a water tow-tank facility.
Abstract: This paper presents experimental results on separation-bubble transition at low Reynolds number and low freestream turbulence, measured on an airfoil using particle image velocimetry (PIV). The two-dimensional PIV measurements have been performed over the suction surface of a low-Reynolds-number airfoil in a water tow-tank facility. Reynolds numbers, based on airfoil chord length and towing speed, of 40,000 and 65,000 have been examined at various angles of incidence, providing a range of streamwise pressure distributions and transitional separation-bubble geometries. The types of bubbles observed range from a short and thick bubble with separation near the leading edge of the airfoil, to a long and thin bubble with separation far downstream of the suction peak. The PIV measurements facilitate visualization of the vortex dynamics associated with separation-bubble transition. The growth of instability waves within the separated shear layer and eventual breakdown into turbulence is documented through the instantaneous vector fields. For all cases examined, large-scale vortex shedding and multiple reverse-flow zones are observed in the reattachment region. A technique for estimating the location of transition onset based on statistical turbulence quantities is presented, and comparisons are made to existing transition models.Copyright © 2005 by ASME
55 citations