Experimental Investigation of a Three-Dimensional Boundary Layer Flow in the Vicinity of an Upright Wall Mounted Cylinder (Data Bank Contribution)

1992 ◽  
Vol 114 (4) ◽  
pp. 566-576 ◽  
Author(s):  
J. H. Agui ◽  
J. Andreopoulos
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Large Scale ◽  
Laser Sheet ◽  
Three Dimensional ◽  
Data Bank ◽  
Separation Point ◽  
Primary Vortex ◽  
Dimensional Boundary ◽  
The Mean

The flow of a three-dimensional boundary layer approaching an upright wall mounted circular cylinder has been experimentally investigated by means of instantaneous flow visualization techniques using a laser sheet and time resolved measurements of the wall pressure, the gradients of which are related to the vorticity flux away from the wall. The mean separation point of the oncoming boundary layer is located on the plane of symmetry, 0.76 and 0.82 diameters upstream of the cylinder for the two investigated Reynolds numbers, based on the cylinder diameter, of 1.0 × 105 and 2.2 × 105, respectively. The present flow visualization studies have shown that there is always a primary vortex present in the flow which induces an eruption of wall fluid. Very often, this eruption results in the formation of counter rotating or mushroom vortices. A secondary vortex further upstream has been observed occasionally. This vortex, as well as the vortices formed by the fast eruption of wall fluid evolve quickly in time and space and therefore cannot be obtained from time-average measurements. The primary vortex consists of several large scale structures which have originated in the oncoming boundary layer and which have acquired substantial additional vorticity. Point measurements indicate that the r.m.s. pressure fluctuations increase as separation is approached and reach a maximum near reattachment. A low degree of space-time correlation and longer integral time scales were also observed downstream of separation. A bimodal probability density function of the fluctuating pressure was observed in the vicinity of the mean separation point, close to the corner region and in the wake of the cylinder. Quasi periodic vortex shedding from the cylinder with a Strouhal number 0.13 was also observed.

scholarly journals Transitional Flow Dynamics Behind a Micro-Ramp

2019 ◽  
Vol 104 (2-3) ◽  
pp. 533-552
Author(s):  
J. Casacuberta ◽  
K. J. Groot ◽  
Q. Ye ◽  
S. Hickel
Keyword(s):  
Boundary Layer ◽  
Stability Analysis ◽  
Large Scale ◽  
Vortex Pair ◽  
Base Flow ◽  
Transitional Flow ◽  
Mean Flow ◽  
Primary Vortex ◽  
The Mean ◽  
Near Wall

AbstractMicro-ramps are popular passive flow control devices which can delay flow separation by re-energising the lower portion of the boundary layer. We compute the laminar base flow, the instantaneous transitional flow, and the mean flow around a micro-ramp immersed in a quasi-incompressible boundary layer at supercritical roughness Reynolds number. Results of our Direct Numerical Simulations (DNS) are compared with results of BiLocal stability analysis on the DNS base flow and independent tomographic Particle Image Velocimetry (tomo-PIV) experiments. We analyse relevant flow structures developing in the micro-ramp wake and assess their role in the micro-ramp functionality, i.e., in increasing the near-wall momentum. The main flow feature of the base flow is a pair of streamwise counter-rotating vortices induced by the micro-ramp, the so-called primary vortex pair. In the instantaneous transitional flow, the primary vortex pair breaks up into large-scale hairpin vortices, which arise due to linear varicose instability of the base flow, and unsteady secondary vortices develop. Instantaneous vortical structures obtained by DNS and experiments are in good agreement. Matching linear disturbance growth rates from DNS and linear stability analysis are obtained until eight micro-ramp heights downstream of the micro-ramp. For the setup considered in this article, we show that the working principle of the micro-ramp is different from that of classical vortex generators; we find that transitional perturbations are more efficient in increasing the near-wall momentum in the mean flow than the laminar primary vortices in the base flow.

Experimental Investigation of Three-Dimensional Secondary Flow on the Endwall of a Blade Channel in an Axial Turbine Cascade

2000 ◽  
Author(s):  
Arkadiy F. Slitenko ◽  
Yuriy M. Jukov
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Preliminary Analysis ◽  
Large Scale ◽  
Three Dimensional ◽  
Generalized Equations ◽  
Turbine Cascade ◽  
Blade Cascade ◽  
Integral Characteristics ◽  
Dimensional Boundary

The local and integral characteristics of three-dimensional boundary layer were investigated in a large scale turbine blade cascade. The flow visualization was carried out for preliminary analysis of the flow structure on the endwall of a blade channel. Then the distribution of velocity components and flow angles in three-dimensional boundary layers was measured in detail. On the basis of the investigation results the generalized equations for calculation of boundary layer characteristics were determined.

Turbulence measurements in a three-dimensional boundary layer in supersonic flow

1998 ◽  
Vol 372 ◽  
pp. 1-23 ◽  
Author(s):  
WOLFGANG KONRAD ◽  
ALEXANDER J. SMITS
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Hot Wire ◽  
Mean Flow ◽  
Turbulence Measurements ◽  
Stabilizing Effect ◽  
Dimensional Boundary ◽  
History Of ◽  
The Mean ◽  
Mach 3

Turbulence measurements were obtained in a three-dimensional supersonic turbulent boundary layer. A 20° curved fin was used to generate a three-dimensional compression of a boundary layer at Mach 3 in the absence of shock waves. Data include hot-wire measurements of five components of the Reynolds stress tensor. The results are interpreted in terms of the mean flow field history of the turbulence. It is demonstrated that in-plane curvature can have a strong stabilizing effect on the turbulence.

The mean velocity profile in three-dimensional turbulent oundary layers

1963 ◽  
Vol 15 (3) ◽  
pp. 368-384 ◽  
Author(s):  
H. G. Hornung ◽  
P. N. Joubert
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Three Dimensional ◽  
Leading Edge ◽  
Viscous Sublayer ◽  
Scale Model ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
The Mean

The mean velocity distribution in a low-speed three-dimensional turbulent boundary-layer flow was investigated experimentally. The experiments were performed on a large-scale model which consisted of a flat plate on which secondary flow was generated by the pressure field introduced by a circular cylinder standing on the plate. The Reynolds number based on distance from the leading edge of the plate was about 6 x 106.It was found that the wall-wake model of Coles does not apply for flow of this kind and the model breaks down in the case of conically divergent flow with rising pressure, for example, in the results of Kehl (1943). The triangular model for the yawed turbulent boundary layer proposed by Johnston (1960) was confirmed with good correlation. However, the value ofyuτ/vwhich occurs at the vertex of the triangle was found to range up to 150 whereas Johnston gives the highest value as about 16 and hence assumes that the peak lies within the viscous sublayer. Much of his analysis is based on this assumption.The dimensionless velocity-defect profile was found to lie in a fairly narrow band when plotted againsty/δ for a wide variation of other parameters including the pressure gradient. The law of the wall was found to apply in the same form as for two-dimensional flow but for a more limited range ofy.

scholarly journals Boundary Layer Characteristics on the Buckets of a Large-Scale Turbine Stage: Part 1 — Profiles of Mean and Turbulent Velocity Vectors

1970 ◽  
Author(s):  
W. H. Day
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Three Dimensional ◽  
Turbulent Velocity ◽  
Velocity Magnitude ◽  
Dimensional Boundary ◽  
Layer Flow ◽  
Flow Effects ◽  
Visualization Techniques ◽  
High Degree

Data have been obtained on details of the three-dimensional boundary layer flow on rotating turbine buckets using hot-wire anemometer and flow visualization techniques. Profiles of velocity magnitude and two angular directions are presented for both the mean and turbulent velocity vectors, as well as profiles of the three products of fluctuating velocities. The data were obtained along six flow paths covering the pressure and suction sides at three radial heights. A high degree of turbulence relative to the rotating buckets was found at all points in the boundary layer on both the pressure and suction sides. Also three-dimensional (radial flow) effects in the boundary layer were significant.

scholarly journals Coherent structure of the convective boundary layer derived from large-eddy simulations

1989 ◽  
Vol 200 ◽  
pp. 511-562 ◽  
Author(s):  
Helmut Schmidt ◽  
Ulrich Schumann
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Large Scale ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Stable Layer ◽  
Convective Boundary ◽  
Velocity Fluctuations ◽  
Large Eddy ◽  
The Mean

Turbulence in the convective boundary layer (CBL) uniformly heated from below and topped by a layer of uniformly stratified fluid is investigated for zero mean horizontal flow using large-eddy simulations (LES). The Rayleigh number is effectively infinite, the Froude number of the stable layer is 0.09 and the surface roughness height relative to the height of the convective layer is varied between 10−6 and 10−2. The LES uses a finite-difference method to integrate the three-dimensional grid-volume-averaged Navier–Stokes equations for a Boussinesq fluid. Subgrid-scale (SGS) fluxes are determined from algebraically approximated second-order closure (SOC) transport equations for which all essential coefficients are determined from the inertial-range theory. The surface boundary condition uses the Monin–Obukhov relationships. A radiation boundary condition at the top of the computational domain prevents spurious reflections of gravity waves. The simulation uses 160 × 160 × 48 grid cells. In the asymptotic state, the results in terms of vertical mean profiles of turbulence statistics generally agree very well with results available from laboratory and atmospheric field experiments. We found less agreement with respect to horizontal velocity fluctuations, pressure fluctuations and dissipation rates, which previous investigations tend to overestimate. Horizontal spectra exhibit an inertial subrange. The entrainment heat flux at the top of the CBL is carried by cold updraughts and warm downdraughts in the form of wisps at scales comparable with the height of the boundary layer. Plots of instantaneous flow fields show a spoke pattern in the lower quarter of the CBL which feeds large-scale updraughts penetrating into the stable layer aloft. The spoke pattern has also been found in a few previous investigations. Small-scale plumes near the surface and remote from strong updraughts do not merge together but decay while rising through large-scale downdraughts. The structure of updraughts and downdraughts is identified by three-dimensional correlation functions and conditionally averaged fields. The mean circulation extends vertically over the whole boundary layer. We find that updraughts are composed of quasi-steady large-scale plumes together with transient rising thermals which grow in size by lateral entrainment. The skewness of the vertical velocity fluctuations is generally positive but becomes negative in the lowest mesh cells when the dissipation rate exceeds the production rate due to buoyancy near the surface, as is the case for very rough surfaces. The LES results are used to determine the root-mean-square value of the surface friction velocity and the mean temperature difference between the surface and the mixed layer as a function of the roughness height. The results corroborate a simple model of the heat transfer in the surface layer.

Heat Transfer Through a Pressure-Driven Three-Dimensional Boundary Layer

1991 ◽  
Vol 113 (2) ◽  
pp. 355-362 ◽  
Author(s):  
S. D. Abrahamson ◽  
J. K. Eaton
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Transfer Data ◽  
Transverse Pressure ◽  
Dimensional Boundary ◽  
The Mean ◽  
Two Dimensional Flows

An experimental investigation of heat transfer through a three-dimensional boundary layer has been performed. An initially two-dimensional boundary layer was made three dimensional by a transverse pressure gradient caused by a wedge obstruction, which turned the boundary layer within the plane of the main flow. Two cases, with similar streamwise pressure gradients and different lateral gradients, were studied so that the effect of the lateral gradient on heat transfer could be deduced. The velocity flowfield agreed with previous hydrodynamic investigations of this flow. The outer parts of the mean velocity profiles were shown to agree with the Squire-Winter theorem for rapidly turned flows. Heat transfer data were collected using a constant heat flux surface with embedded thermocouples for measuring surface temperatures. Mean fluid temperatures were obtained using a thermocouple probe. The temperature profiles, when plotted in outer scalings, showed logarithmic behavior consistent with two-dimensional flows. An integral analysis of the boundary layer equations was used to obtain a vector formulation for the enthalpy thickness, HH≜∫0∞ρuisdyρ∞ii,o(u∞2+w∞2)1/2,0,∫0∞ρwisdyρ∞is,o(u∞2+w∞2)1/2 (where is is the stagnation enthalpy), which is consistent with the scalar formulation used for two-dimensional flows. Using the vector formulation, the heat transfer data agreed with standard two-dimensional correlations of the Stanton number and enthalpy thickness Reynolds number. It was concluded that although the heat transfer coefficient decreased faster than its two-dimensional counterpart, it was similar to the two-dimensional case. The vector form of the enthalpy thickness captured the rotation of the mean thermal energy flux away from the free-stream direction. Boundary layer three dimensionality increased with the strength of the transverse pressure gradient and the heat transfer coefficients were smaller for the stronger transverse gradient.

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