On the Characteristics of Incompressible Turbulent Boundary Layers (original) (raw)

An investigation of turbulence structure in a low Reynolds number incompressible turbulent boundary layer

Hot-wire anemometry measurements in an incompressible turbulent boundary-layer flow over a flat plate at zero pressure gradient were made using two X-probes simultaneously. The experiment was performed in the large Atmospheric Boundary-Layer Wind Tunnel at the University of California, Davis. The 7.32 meter long flat plate installed within the wind tunnel generated approximately 20 cm thick boundary layer, R (sub theta) approximately 4,000. Mean velocity and turbulence intensity data very close to the wall (y(+) is greater than or = to 1) were measured with a single hot wire to improve the measurement resolution. Space-time correlations of mu' and upsilon' velocities and of their instantaneous product were obtained with a pair of X-wires. The mean convection velocities, the extent in space, the mean inclination angles, and coherence characteristics of the mu', upsilon' and (mu')(upsilon') large-scale structures are presented. (The (mu')(upsilon') resu...

Interfaces and internal layers in a turbulent boundary layer

Physics of Fluids, 2015

New experimental research is presented on the characteristics of interfaces and internal shear layers that are present in a turbulent boundary layer (TBL). The turbulent/non-turbulent (T/NT) interface at the outer boundary of the TBL shows the presence of a finite jump in streamwise velocity and is characterised by a thin shear layer. It appears that similar layers of high shear occur also within the TBL which separate regions of almost uniform momentum. It turns out that they exhibit similar characteristics as the external T/NT interface. Furthermore, the spatial growth rate of the TBL, that is derived from theoretical analysis, can be correctly predicted from a momentum balance near the external T/NT interface. Similarly, the entrainment velocities for the average internal layers have been determined. Results indicate that internal layers move slower in the vicinity of the wall, whereas they move faster than the large scale boundary layer growth rate in the outer region of the TBL. It is believed that shear layers bound large scale flow regions of approximately uniform momentum. Hence, the entrainment velocities of these internal layers may be interpreted as growth rates of the large scale motions in a TBL.

Analytic model of the universal structure of turbulent boundary layers

Jetp Letters, 2006

Turbulent boundary layers exhibit a universal structure that nevertheless is rather complex and is composed of a viscous sublayer, a buffer zone, and a turbulent log-law region. In this letter, we present a simple analytic model of turbulent boundary layers that culminates in explicit formulas for the profiles of the mean velocity, the kinetic energy, and the Reynolds stress as a function of the distance from the wall. The resulting profiles are in close quantitative agreement with measurements over the entire structure of the boundary layer without any need of refitting in the different zones.

Turbulent boundary layers up to Re[sub θ]=2500 studied through simulation and experiment

Physics of Fluids, 2009

Direct numerical simulations ͑DNSs͒ and experiments of a spatially developing zeropressure-gradient turbulent boundary layer are presented up to Reynolds number Re = 2500, based on momentum thickness and free-stream velocity. For the first time direct comparisons of DNS and experiments of turbulent boundary layers at the same ͑computationally high and experimentally low͒ Re are given, showing excellent agreement in skin friction, mean velocity, and turbulent fluctuations. These results allow for a substantial reduction of the uncertainty of boundary-layer data, and cross validate the numerical setup and experimental technique. The additional insight into the flow provided by DNS clearly shows large-scale turbulent structures, which scale in outer units growing with Re , spanning the whole boundary-layer height.

Progress in simulations of turbulent boundary layers

2011

Recent efforts in the simulation of turbulent boundary layers using direct and large-eddy simulations are described. The focus is naturally on a series of simulations performed at KTH Stockholm. These results have been used to examine various aspects of the boundary layer; starting from estimates of the extent of the transitional region, the detailed comparison to wind-tunnel experiments, the effect of ambient freestream turbulence on the boundary layer and to quantifications of the spectral composition of the turbulent signal. Furthermore, selected aspects of boundary layers with coupled scalar (e.g. heat) transport are summarised, including profiles of the turbulent Prandtl number Pr t .

New aspects of turbulent boundary-layer structure

Journal of Fluid Mechanics, 1981

Flow visualization studies of the zero-pressure-gradient turbulent boundary layer over the Reynolds-number range 500 < Re, < 17500 have shown large Reynoldsnumber effects on boundary-layer structure. At high Reynolds numbers (Re, > 2000, say) the layer appears to consist very largely of elongated hairpin vortices or vortex pairs, originating in the wall region and extending through a large part of the boundary-layer thickness or beyond i t ; they are for the most part inclined to the wall at a characteristic angle in the region of 40-50'. Large-scale features, which exhibit a slow overturning motion, appear t o consist mainly of random arrays of such hairpin vortices, although there is some evidence of more systematic structures. At low Reynolds numbers (Re, < 800, say) the hairpin vortices are very much less elongated and are better described as horseshoe vortices or vortex loops ; large-scale features now consist simply of isolated vortex loops (at the very lowest Reynolds numbers), or of several such loops interacting strongly, and show a relatively brisk rate of rotation. ' This happened more or less automatically with the hot-wire signals displayed on the oscilloscope and photographed along with the illuminated section of the layer, and

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.

Studies on Boundary Layer Parameters on Rough Surfaces in Turbulent Boundary Layer Zone

2015

At the point when genuine fluid streams past a solid body or a solid boundary wall, the fluid particles adhere to the wall and state of no slip happens. This implies that the velocity of fluid near to the wall will be same as that of wall. On the off chance that the wall is stationary, the speed of fluid at the boundary will be zero. Further far from the limit, the velocity will be higher and as a consequence of this variety of velocity, and gradient of velocity will exist. The speed of fluid increments from zero on the stationary limit to the free stream velocity of the fluid in the direction normal to the boundary. This velocity from zero to free stream velocity in the perpendicular direction to the wall happens in a restricted locale in the region of solid boundary. This narrow locale of fluid is called Boundary Layer. Three fundamental parameters (portrayed underneath) that are utilized to describe the size and state of a boundary layer are the nominal boundary layer thickness, ...