Turbulence Measurements Near the Stern of a Ship Model

1984 ◽  
Vol 28 (03) ◽  
pp. 186-201
Author(s):  
Lennart Löfdahl ◽  
Lars Larsson
Keyword(s):  
Boundary Layer ◽  
Strong Influence ◽  
Three Dimensional ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Calculation Methods ◽  
Mean Velocity ◽  
Ship Model ◽  
The Mean ◽  
Stress Profiles

An experimental investigation in which Reynolds stress profiles were measured in the thick three-dimensional turbulent boundary layer at the stern of a ship model has been carried out. The measurements were performed using a specially developed hot-wire technique in which the mean velocity component perpendicular to the surface was considered. A large number of results are given in diagrams, and an error estimation for the different Reynolds stresses is presented. Efforts have been made, when positioning the measured turbulence profiles, to enable future development of calculation methods based on these results. The measured profiles have revealed a strong influence of streamline convergence (divergence) on the Reynolds stresses. Also, the effects of wall curvature are of importance, and since most parts of the investigated region have a convex curvature the average level of the stresses is reduced.

An Explicit Non-Real Time Data Reduction Method of Triple Sensors Hot-Wire Anemometer in Three-Dimensional Flow

1988 ◽  
Vol 110 (2) ◽  
pp. 110-119 ◽  
Author(s):  
Y. T. Chew ◽  
R. L. Simpson
Keyword(s):  
Real Time ◽  
Three Dimensional ◽  
Computation Time ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Time Data ◽  
Three Dimensional Flow ◽  
Mean Velocity ◽  
Dimensional Flow ◽  
The Mean

An explicit non-real time method of reducing triple sensor hot-wire anenometer data to obtain the three mean velocity components and six Reynolds stresses, as well as their turbulence spectra in three-dimensional flow is proposed. Equations which relate explicitly the mean velocity components and Reynolds stresses in laboratory coordinates to the mean and mean square sensors output voltages in three stages are derived. The method was verified satisfactorily by comparison with single sensor hot-wire anemometer measurements in a zero pressure gradient incompressible turbulent boundary layer flow. It is simple and requires much lesser computation time when compared to other implicit non-real time method.

Measurement of the Reynolds stresses and the mean-flow field in a three-dimensional pressure-driven boundary layer

1982 ◽  
Vol 119 ◽  
pp. 121-153 ◽  
Author(s):  
Udo R. Müller
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Field ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Acceleration ◽  
The Mean

An experimental study of a steady, incompressible, three-dimensional turbulent boundary layer approaching separation is reported. The flow field external to the boundary layer was deflected laterally by turning vanes so that streamwise flow deceleration occurred simultaneous with cross-flow acceleration. At 21 stations profiles of the mean-velocity components and of the six Reynolds stresses were measured with single- and X-hot-wire probes, which were rotatable around their longitudinal axes. The calibration of the hot wires with respect to magnitude and direction of the velocity vector as well as the method of evaluating the Reynolds stresses from the measured data are described in a separate paper (Müller 1982, hereinafter referred to as II). At each measuring station the wall shear stress was inferred from a Preston-tube measurement as well as from a Clauser chart. With the measured profiles of the mean velocities and of the Reynolds stresses several assumptions used for turbulence modelling were checked for their validity in this flow. For example, eddy viscosities for both tangential directions and the corresponding mixing lengths as well as the ratio of resultant turbulent shear stress to turbulent kinetic energy were derived from the data.

LDA Measurements on Rough Turbulent Boundary Layers Subject to Strong Favorable Pressure Gradients

2006 ◽  
Author(s):  
Rau´l Bayoa´n Cal ◽  
Brian Brzek ◽  
Gunnar Johansson ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Rough Surface ◽  
Reynolds Stress ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Velocity Deficit ◽  
The Mean ◽  
Stress Profiles

Laser-Doppler anemometry (LDA) measurements of the mean velocity and Reynolds stresses are carried out on a rough surface favorable pressure gradient (FPG) turbulent boundary layer. These data is compared with smooth FPG turbulent boundary layer data possessing with the same strength of pressure gradient and also with rough zero pressure gradient (ZPG) data. The scales for the mean velocity deficit and Reynolds stresses are obtained through means of equilibrium similarity analysis of the RANS equations [1]. The mean velocity deficit profiles collapse, but to different curves when normalized using the free-stream velocity. The effects of the pressure gradient and roughness are clearly distinguished and separated. However, these effects are removed from the outer flow when the profiles are normalized using the Zagarola and Smits [2] scaling. It is also found that there is a clear effect of the roughness and pressure gradient on the Reynolds stresses. The Reynolds stress profiles augment due to the rough surface. Furthermore, the strength of the pressure gradient imposed of the flow changes the shape of the Reynolds stress profiles especially on the < v2 > and < uv > components. The rough surface influence is mostly noticed on the < u2 > component of the Reynolds stress, where the shape of the profiles change entirely. The boundary layer parameter δ*/δ shows the effects of the roughness and a dependence on the Reynolds number for the smooth FPG case. The pressure parameter, A, describes a development of the turbulent boundary layer and no influence of the roughness is linked with the parameter, k+. The boundary layers grow differently and depict the influence of the studied effects in their development. These measurements are the first of their nature due to the extensive number in downstream locations (12) and the combination of the studied external conditions (i.e., the strength of the pressure gradient and the surface roughness).

Turbulent Boundary Layers Over Surfaces Smoothed by Sanding

2003 ◽  
Vol 125 (5) ◽  
pp. 863-870 ◽  
Author(s):  
Michael P. Schultz ◽  
Karen A. Flack
Keyword(s):  
Boundary Layer ◽  
Skin Friction Coefficient ◽  
Laser Doppler Velocimeter ◽  
Reynolds Stresses ◽  
Smooth Wall ◽  
Mean Velocity ◽  
Towing Tank ◽  
The Mean ◽  
Stress Profiles ◽  
Similarity Law

Flat-plate turbulent boundary layer measurements have been made on painted surfaces, smoothed by sanding. The measurements were conducted in a closed return water tunnel, over a momentum thickness Reynolds number Reθ range of 3000 to 16,000, using a two-component laser Doppler velocimeter (LDV). The mean velocity and Reynolds stress profiles are compared with those for smooth and sandgrain rough walls. The results indicate an increase in the boundary layer thickness (δ) and the integral length scales for the unsanded, painted surface compared to a smooth wall. More significant increases in these parameters, as well as the skin-friction coefficient Cf were observed for the sandgrain surfaces. The sanded surfaces behave similarly to the smooth wall for these boundary layer parameters. The roughness functions ΔU+ for the sanded surfaces measured in this study agree within their uncertainty with previous results obtained using towing tank tests and similarity law analysis. The present results indicate that the mean profiles for all of the surfaces collapse well in velocity defect form. The Reynolds stresses also show good collapse in the overlap and outer regions of the boundary layer when normalized with the wall shear stress.

scholarly journals EFFECT OF RIBLETS AND SUCTION ON A FLAT PLATE TURBULENT BOUNDARY LAYER

2006 ◽  
Vol 5 (1) ◽  
pp. 78
Author(s):  
M. O. Oyewola
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Smooth Surface ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Smooth Wall ◽  
Mean Velocity ◽  
Layer Structures ◽  
Porous Strip ◽  
The Mean

This work presents hot-wire measurements in a flat plate turbulent boundarylayer, subjected to the combination of riblets and suction. The suction is applied through a porous strip for a range of suction rates. The effect of riblets and suction has been quantified through the measurements of mean velocity and Reynolds stresses downstream of the suction strip on the riblets surface. The results of the mean velocity and Reynolds stresses indicate that there is no significant change in the distributions of riblets and smooth wall. However, there exist some changes with the combination of suction and riblets relative to the smooth surface. These changes arise from the interference of suction with the mechanism of the layer. The results suggest that riblets may not alter the effect suction has on the boundary layer structures.

The Structure of a Boundary Layer on a Rough Wall with Blowing and Heat Transfer

1979 ◽  
Vol 101 (2) ◽  
pp. 193-198 ◽  
Author(s):  
M. M. Pimenta ◽  
R. J. Moffat ◽  
W. M. Kays
Keyword(s):  
Boundary Layer ◽  
Correlation Coefficients ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Mean Velocity ◽  
Length Constant ◽  
The Mean

A regular, deterministic, rough surface was tested at four velocities from 11 to 40 m/s, with and without blowing, to evaluate the Stanton number and friction factor characteristics. Hot-wire data were taken to document the turbulence components, the Reynolds stresses, and the turbulent heat flux. Data are presented concerning the streamwise development of the mean and fluctuating components, and the effect of blowing. Correlation coefficients and mixing lengths were deduced from the hot-wire data and are also presented. While the mean velocity data showed only two allowable states for the boundary layer (laminar and “fully rough”), the turbulence structure indicated a third: “transitionally rough”. Distributions of u′v′/uτ2 and v′t′/uτtτ are similar, except for high blowing (F = 0.004). The turbulent Prandtl number lies between 0.85 and 1.0 for the entire layer, and a mixing length constant of κ = 0.41 describes the data with good accuracy for all velocities and all values of blowing tested.

Hot Wire Measurements at the Exit of a Centrifugal Compressor Impeller

1979 ◽  
Vol 193 (1) ◽  
pp. 341-347
Author(s):  
A. Goulas ◽  
R. C. Baker
Keyword(s):  
Centrifugal Compressor ◽  
Magnetic Tape ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Mean Velocity ◽  
Isentropic Flow ◽  
Compressor Impeller ◽  
The Mean

Hot wire measurements at the exit of a small centrifugal compressor impeller are reported. Three different hot wire readings were obtained and stored on a magnetic tape for each point by gating the analogue hot wire signal with a pulse which indicated circumferential position. The combination of the three readings yielded the mean velocity and some Reynolds stresses at each point. The measurements show a ‘jet-wake’ profile towards the shroud and ‘isentropic’ flow near the hub.

Intermittency measurements in the turbulent boundary layer

1966 ◽  
Vol 25 (4) ◽  
pp. 719-735 ◽  
Author(s):  
H. Fiedler ◽  
M. R. Head
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Focal Point ◽  
Pressure Gradients ◽  
Narrow Beam ◽  
Hot Wire ◽  
Characteristic Parameters ◽  
Mean Velocity ◽  
Form Parameter ◽  
The Mean

An improved version of Corrsin & Kistler's method has been used to measure intermittency in favourable and adverse pressure gradients, and the characteristic parameters of the intermittency have been related to the form parameterHof the mean velocity profiles.It is found that with adverse pressure gradients the centre of intermittency moves outward from the surface while the width of the intermittent zone decreases. The converse is true of favourable pressure gradients, and it seems likely that at sufficiently low values ofHthe flow over the full depth of the layer is only intermittently turbulent.A new method of intermittency measurement is presented which makes use of a photo-electric probe. Smoke is introduced into the boundary layer and illuminated by a narrow beam of parallel light normal to the surface. The photoelectric probe is focused on the illuminated region and a signal is generated when smoke passes through the focal point of the probe lens. Comparison of this signal with the output from a hot-wire at very nearly the same point shows the identity of smoke and turbulence distributions.

A three-dimensional turbulent boundary layer

1965 ◽  
Vol 22 (2) ◽  
pp. 285-304 ◽  
Author(s):  
A. E. Perry ◽  
P. N. Joubert
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Three Dimensional ◽  
Outer Part ◽  
Outer Region ◽  
Experimental Results ◽  
Mean Velocity ◽  
Polar Plot ◽  
Law Of The Wall ◽  
The Mean

The purpose of this paper is to provide some possible explantions for certain observed phenomena associated with the mean-velocity profile of a turbulent boundary layer which undergoes a rapid yawing. For the cases considered the yawing is caused by an obstruction attached to the wall upon which the boundary layer is developing. Only incompressible flow is considered.§1 of the paper is concerned with the outer region of the boundary layer and deals with a phenomenon observed by Johnston (1960) who described it with his triangular model for the polar plot of the velocity distribution. This was also observed by Hornung & Joubert (1963). It is shown here by a first-approximation analysis that such a behaviour is mainly a consequence of the geometry of the apparatus used. The analysis also indicates that, for these geometries, the outer part of the boundary-layer profile can be described by a single vector-similarity defect law rather than the vector ‘wall-wake’ model proposed by Coles (1956). The former model agrees well with the experimental results of Hornung & Joubert.In §2, the flow close to the wall is considered. Treating this region as an equilibrium layer and using similarity arguments, a three-dimensional version of the ‘law of the wall’ is derived. This relates the mean-velocity-vector distribution with the pressure-gradient vector and wall-shear-stress vector and explains how the profile skews near the wall. The theory is compared with Hornung & Joubert's experimental results. However at this stage the results are inconclusive because of the lack of a sufficient number of measured quantities.

Separated and Reattached Flow Over Square, Rectangular and Semi-Circular Blocks

2007 ◽  
Author(s):  
M. Agelinchaab ◽  
M. F. Tachie
Keyword(s):  
Boundary Layer ◽  
Cross Sections ◽  
Recirculation Region ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Block Height ◽  
Turbulent Statistics ◽  
Image Velocimetry ◽  
The Mean ◽  
Separated And Reattached Flow

A particle image velocimetry is used to study the characteristics of separated and reattached turbulent flow over two-dimensional transverse blocks of square, rectangular and semi-circular cross-sections fixed to the bottom wall of an open channel. The ratio of upstream boundary layer thickness to block height is considerably higher than in prior studies. The results show that the mean and turbulent statistics in the recirculation region and downstream of reattachment are significantly different from the upstream boundary layer. The variation of the Reynolds stresses along the separating streamlines is discussed within the context of vortex stretching, longitudinal strain rate and wall damping. It appears wall damping is a more dominant mechanism in the vicinity of reattachment. The levels of turbulence diffusion and production by the normal stresses are significantly higher than in classical turbulent boundary layers. The bulk of turbulence production occurs in mid-layer and transported into the inner and outer layers. The results also reveal that the curvature of separating streamline, separating bubble beneath it as well as the mean velocity and turbulent quantities depend strongly on block geometry.

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