Response of Spatially Developing Turbulent Boundary Layer to Spanwise Oscillating Electromagnetic Force (original) (raw)
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Journal of Turbulence, 2005
Direct numerical simulations were performed to investigate the physics of a spatially-developing turbulent boundary layer flow subjected to spanwise oscillating electromagnetic force. The electromagnetic force beneath the flat plate was locally given with a finite length. A fully implicit fractional step method was employed to simulate the flow. The mean flow properties and the Reynolds stresses were obtained to analyze the nearwall turbulent structure. The skin friction and turbulent kinetic energy can be reduced by the electromagnetic forces. In the absence of the electromagnetic force, the flow eventually relaxes back to a two-dimensional equilibrium boundary layer.
EXPERIMENTAL AND NUMERICAL STUDY ON TURBULENT OSCILLATORY BOUNDARY LAYERS
An experimental and numerical study covering various boundary layer properties under oscillatory and pulsatile motion has been carried out. The experiments were performed by using oscillating tunnel and the detailed measurement of velocity was carried out by Laser Doppler Velocimeter(LDV ) under various flow conditions. The numerical computations were m ade by using low Reynolds number k -E model.
Turbulent boundary layer flow subject to streamwise oscillation of spanwise wall-velocity
Direct numerical simulations have been performed to study the effect of a stationary distribution of spanwise wall-velocity that oscillates in the streamwise direction on a turbulent boundary layer. For the first time, a spatially developing flow with this type of forcing is studied. The part of the boundary layer which flows over the alternating wall-velocity section is greatly affected with a drag reduction close to 50% which exhibits an oscillatory distribution with a wavenumber which is twice that of the imposed wall-velocity. The maximum in drag reduction occurs where the wall velocity is at its maximum (or minimum) and the minimum occurs where the wall velocity is zero. Comparisons of the mean spanwise velocity profiles with the analytical solution to the laminar Navier-Stokes equations show very good agreement. The streamwise velocity profile indicates a thickening of the viscous sub-layer when scaled with the local friction velocity and an upward shifting of the logarithmic region when scaled with the reference (unmanipulated) friction velocity. An estimation of the idealized power consumption shows that-with the present wall forcing magnitude-more energy is required for the spatial oscillation than what is saved by drag reduction.
Analytical model of the time developing turbulent boundary layer
JETP Letters, 2007
We present an analytical model for the time-developing turbulent boundary layer (TD-TBL) over a flat plate. The model provides explicit formulae for the temporal behavior of the wall-shear stress and both the temporal and spatial distributions of the mean streamwise velocity, the turbulence kinetic energy and Reynolds shear stress. The resulting profiles are in good agreement with the DNS results of spatially-developing turbulent boundary layers at momentum thickness Reynolds number equal to 1430 and 2900 [1-3]. Our analytical model is, to the best of our knowledge, the first of its kind for TD-TBL.
Studies of turbulent boundary layer flow through direct numerical simulation
2001
The objective has been to study turbulent boundary layers under adverse pressure gradients (APG) through direct numerical simulation (DNS). The numerical code is based on a pseudo-spectral technique which is suitable for the simple geometry (flat plate) considered here. A large effort has been put into the optimization of the numerical code on various super computers. Five large simulations have been performed, ranging from a zero pressure gradient boundary layer to a separating flow. The simulations have revealed many features of APG turbulent boundary layers which are difficult to capture in experiments. Especially the near-wall behavior has been investigated thoroughly, both through the statistical and instantaneous flow.
Temporal and spatial transients in turbulent boundary layer flow over an oscillating wall
Direct Numerical Simulations have been performed to study the effect of an oscillating segment of the wall on a turbulent boundary layer flow. Two different oscillation amplitudes with equal oscillation period have been used, which allows a direct comparison between a relatively weak and strong forcing of the flow. The weaker forcing results in 18% drag reduction while the stronger forcing, with twice the amplitude, yields 29% drag reduction. The downstream development of the drag reduction is compared with earlier simulations and experiments. In addition, a simulation with identical oscillation parameters as in previous numerical and experimental investigations allows for an estimation of the effect of the Reynolds number on the drag reduction.
On the turbulent boundary layer over a flat plate at moderate Reynolds numbers
Physics of Fluids
Two separate experimental campaigns of a spatially developing turbulent boundary layer under approximately zero-pressure-gradient at moderate Reynolds numbers ([Formula: see text]) are conducted with stereoscopic Particle Image Velocimetry (PIV) and one component Hot Wire Anemometry. This range of Reynolds numbers is found to be of particular interest for turbulent boundary layer control investigations. The motivations behind this work rely on the lack of recent studies that provide a rigorous experimental database on a flat plate turbulent boundary layer, openly available online. This is critical as, in most of the cases, the modification of the statistics resulting from turbulent boundary layer control strategies are compared with a smooth baseline reference. The statistics of the velocity fields, obtained with the two techniques, show a good match with the direct numerical simulation in literature results. We focused on the skin friction evaluation by means of Clauser's chart...
Dynamic behavior of an unsteady turbulent boundary layer
This paper reports experiments on an unsteady turbulent boundary layer. The upstream portion of the flow is steady (in the mean). In the downstream region, the boundary layer saes a linearly decreasing free-stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. Considerable detail is reported for a low-amplitude case, and preliminary results are given for a higher amplitude sufficient to produce some reverse flow. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as such as 70Z greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and tLe Raynolds stress distribution across the boundary layer become frozen. The behavior at larger amplitude is quite similar. Most importantly, at sufficiently high frequencies the boundary layer thickness remains frozen at its mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle.
A Simple Model for Turbulent Boundary Layer Momentum Transfer on a Flat Plate
Chemical Engineering & Technology, 2000
A simple model is presented for turbulent momentum transfer on a flat plate. The proposed model is based on some polynomial velocity profiles in a laminar sublayer as well as in a fully developed boundary layer and two integral boundary layer equations. The model could be used for the calculation of boundary layer thickness, velocity profile and skin friction factor on the flat plate. The calculated results are in very good agreement with other proposed empirical correlations.
Experimental and Numerical Study on Turbulent Oscillatory Boundary Layer
D. Eng. Diss, 1997
An experimental and numerical study covering various boundary layer properties under oscillatory and pulsatile motion has been carried out. The experiments were performed by using oscillating t unnel and the detailed measurement of velocity was carried out by Laser Doppler Velocimeter(LDV) under various flow conditions. The numerical computations were m ade by using low Reynolds number k -E model.