Changes of the mean velocity profiles in the combined wave–current motion described in a GLM formulation

1998 ◽  
Vol 370 ◽  
pp. 271-296 ◽  
Author(s):  
J. GROENEWEG ◽  
G. KLOPMAN
Keyword(s):  
Velocity Profiles ◽  
Perturbation Series ◽  
Wave Crest ◽  
Mean Velocity ◽  
Initial Current ◽  
Eulerian Formulation ◽  
Waves And Currents ◽  
The Mean ◽  
The Waves ◽  
A Current

The generalized Lagrangian mean (GLM) formulation is used to describe the interaction of waves and currents. In contrast to the more conventional Eulerian formulation the GLM description enables splitting of the mean and oscillating motion over the whole depth in an unambiguous and unique way, also in the region between wave crest and trough. The present paper deals with non-breaking long-crested regular waves on a current using the GLM formulation coupled with a WKBJ-type perturbation-series approach. The waves propagate under an arbitrary angle with the current direction. The primary interest concerns nonlinear changes in the vertical distribution of the mean velocity due to the presence of the waves, but modifications of the orbital velocity profiles, due to the presence of a current, are considered as well. The special case of no initial current, where waves induce a so-called drift velocity or mass-transport velocity, is also studied.

Experimental Study on Mean Velocity Profiles Under Wave-Current Interactions

2008 ◽  
Author(s):  
Jinhai Zheng ◽  
Tongfei Li ◽  
Yixin Yan ◽  
Jinchun Hu
Keyword(s):  
River Estuary ◽  
Maximum Velocity ◽  
Velocity Profiles ◽  
Yangtze River Estuary ◽  
Current Profile ◽  
Linear Superposition ◽  
Mean Velocity ◽  
The Mean ◽  
Logarithmic Law ◽  
A Current

A series of experiments are carried out in a laboratory flume for combined wave-current flows, to investigate the characteristics of vertical structure of current profile in a wave-current co-existing water areas. Changes induced in the mean velocity profiles are considered for a range of wave heights, wave periods, water depths and flow velocities which are based on those typical data in the Yangtze River Estuary, China. Preliminary tests are conducted on the unidirectional current and on the wave alone. These show that the current mean velocity profiles agree well with the logarithmic law, and that the waves are approximated closely by the Stokes’ second-order theory. For the combined wave and current tests, the mean velocity profiles generally differ from those suggested by a linear superposition of wave and current velocities. In the case of waves following a current, the velocity distributions exhibit a relatively greater velocity near the bed and a smaller velocity above a certain depth relative to the logarithmic law, and the maximum velocity is observed at a lower location. In the case of wave opposing a current, the velocity distributions depart from the logarithmic law with a relatively smaller velocity near the bed and a greater velocity above a certain depth. Experimental data can be used to validate the theoretical or mathematical models associated with the combined wave-current motions.

Investigation of Boundary Layer Flows Over a Flat Plate With Different-Size Transverse Square Grooves at s/w = 10

2007 ◽  
Author(s):  
Redha Wahidi ◽  
Walid Chakroun ◽  
Sami Al-Fahad
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Viscous Sublayer ◽  
Velocity Profiles ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Uncertainty Range ◽  
The Mean

Turbulent boundary layer flows over a flat plate with multiple transverse square grooves spaced 10 element widths apart were investigated. Mean velocity profiles, turbulence intensity profiles, and the distributions of the skin-friction coefficients (Cf) and the integral parameters are presented for two grooved walls. The two transverse square groove sizes investigated are 5mm and 2.5mm. Laser-Doppler Anemometer (LDA) was used for the mean velocity and turbulence intensity measurements. The skin-friction coefficient was determined from the gradient of the mean velocity profiles in the viscous sublayer. Distribution of Cf in the first grooved-wall case (5mm) shows that Cf overshoots downstream of the groove and then oscillates within the uncertainty range and never shows the expected undershoot in Cf. The same overshoot is seen in the second grooved-wall case (2.5mm), however, Cf continues to oscillate above the uncertainty range and never returns to the smooth-wall value. The mean velocity profiles clearly represent the behavior of Cf where a downward shift is seen in the Cf overshoot region and no upward shift is seen in these profiles. The results show that the smaller grooves exhibit larger effects on Cf, however, the boundary layer responses to these effects in a slower rate than to those of the larger grooves.

scholarly journals On the cooling and evaporative powers of the atmosphere, as determined by the kata-thermometer

1919 ◽  
Vol 90 (632) ◽  
pp. 438-447 ◽  
Keyword(s):  
Body Temperature ◽  
Skin Temperature ◽  
Cross Section ◽  
Cooling Power ◽  
Mean Velocity ◽  
Cross Section Area ◽  
Section Area ◽  
Order Of Magnitude ◽  
The Mean ◽  
A Current

In a paper published in ‘Phil. Trans.’ (B, vol. 207, 1916, pp. 183-220) by L. Hill, O. W. Griffiths, and M. Flack, there was detailed the theory and use of an instrument, the kata-thermometer, a large-bulbed alcohol thermometer, for determining the cooling power of the atmosphere on a surface at body temperature. A formula H/ θ = 0⋅27 + 0⋅36 √V, where H = heat lost in mille-calories per square centimetre per second, θ = (36⋅5— t )°C., where t = temperature of enclosure, and V = velocity of air current in metres per second, was obtained for the loss of heat of the dry kata-thermometer in a current of air; 36⋅5° C. was chosen as the skin temperature. This is a variable, and only reaches that figure in warm atmospheres. The constant 0⋅36 in the above formula was determined from experiments which were carried out with the apparatus then available in a tube of which the cross-section area was of the same order of magnitude as that of the kata. Therefore, in calculating the velocity of the air current i.e ., the mean velocity of the air striking the kata, the area of cross-section of the kata was subtracted from that of the tube.

Fractal Orifices for Flowmetering

2012 ◽  
Author(s):  
Franck C. G. A. Nicolleau ◽  
Stephen B. M. Beck ◽  
Andrzej F. Nowakowski
Keyword(s):  
Wind Tunnel ◽  
Flow Rate ◽  
Velocity Profiles ◽  
Symmetric Design ◽  
Flow Properties ◽  
Mean Velocity ◽  
Fractal Pattern ◽  
The Mean

In this article we study the return to axi-symmetry for a flow generated after fractal plates in a circular wind tunnel. We consider two sets of plates: one orifice-like and one perforated-like. The mean velocity profiles are presented at different distances from the plate and we study the convergence of a flow rate based on these profiles. The return to axi-symmetry depends on how far was the original plate from an axi-symmetric design. It also depends on the level of iteration of the fractal pattern. In line with results for other flow properties [1, 2] It seems that there is not much to be gained by manufacturing fractal plates with more than three iteration levels.

The turbulent boundary layer over a wall with progressive surface waves

1970 ◽  
Vol 41 (2) ◽  
pp. 259-281 ◽  
Author(s):  
James M. Kendall
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
Rubber Sheet ◽  
Pressure Drag ◽  
Generation Theory ◽  
The Mean ◽  
The Waves ◽  
Vertical Height

An experimental study of the interaction of a turbulent boundary layer with a wavy wall was conducted in a wind tunnel. A smooth neoprene rubber sheet comprising a portion of the floor of the tunnel was mechanically deformed into 12 sinusoidal waves which progressed upwind or down at controlled speed. The turbulent layer thickness was a little less than the wavelength. The mean velocity profile was linear on a semi-log plot over a substantial range of vertical height.The wall pressure was observed to be asymmetrical about the wave profile, resulting in a pressure drag. Flow separation was not the cause of the drag. The drag was found to be larger than that predicted by the inviscid wave generation theory. The measurements indicate that the waves strongly modulate the turbulent structure. The phase of the turbulent stresses with respect to the waves varies with wave speed, indicating that the dynamical reaction time of the turbulence is not negligible in comparison with the wave period.

Experimental Investigation of Turbulent Boundary Layers Under Favorable Pressure Gradient

2010 ◽  
Author(s):  
Pranav Joshi ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Pressure Gradient ◽  
Skin Friction ◽  
Velocity Profiles ◽  
Skin Friction Coefficient ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Favorable Pressure Gradient ◽  
The Mean

The goal of this research is to study the effect of favorable pressure gradient (FPG) on the near wall structures of a turbulent boundary layer on a smooth wall. 2D-PIV measurements have been performed in a sink flow, initially at a coarse resolution, to characterize the development of the mean flow and (under resolved) Reynolds stresses. Lack of self-similarity of mean velocity profiles shows that the boundary layer does not attain the sink flow equilibrium. In the initial phase of acceleration, the acceleration parameter, K = v/U2dU/dx, increases from zero to 0.575×10−6, skin friction coefficient decreases and mean velocity profiles show a log region, but lack universality. Further downstream, K remains constant, skin friction coefficient increases and the mean velocity profiles show a second log region away from the wall. In the initial part of the FPG region, all the Reynolds stress components decrease over the entire boundary layer. In the latter phase, they continue to decrease in the middle of the boundary layer, and increase significantly close to the wall (below y∼0.15δ), where they collapse when normalized with the local freestream velocity. Turbulence production and wallnormal transport, scaled with outer units, show self-similar profiles close to the wall in the constant K region. Spanwise-streamwise plane data shows evidence of low speed streaks in the log layer, with widths scaling with the boundary layer thickness.

Sinusoidal Excitation of a Free Turbulent Jet With Constant Amplitude Transverse Pressure Gradients Near the Nozzle Exit: Part I: Measurement of Mean Shear Velocities

1973 ◽  
Vol 95 (2) ◽  
pp. 167-173
Author(s):  
A. K. Stiffler ◽  
J. L. Shearer
Keyword(s):  
Nozzle Exit ◽  
Flow Direction ◽  
Excitation Frequency ◽  
Velocity Profiles ◽  
Turbulent Jet ◽  
Pressure Gradients ◽  
Mean Velocity ◽  
Effective Velocity ◽  
Gaussian Distribution Function ◽  
The Mean

A free turbulent jet is perturbed transverse to the flow direction by a sinusoidal pressure gradient near the nozzle exit. Velocities in the jet are determined by hot wire anemometer measurements. Moving effective mean velocity profiles are defined and reconstructed from the point-by-point stationary measurements of the mean velocity and of the harmonic content of the time varying signal. The effective velocity profiles are described by the Gaussian distribution function where the spread parameter decays as the cube of the product of the excitation frequency and the downstream location from the nozzle. These profile measurements and analysis of their characteristics lead to a better understanding of the factors determining the gain of a fluidic amplifier under conditions of high frequency operation.

scholarly journals Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

2020 ◽  
Vol 5 (10) ◽  
pp. 1199-1203
Author(s):  
Md. Mosharrof Hossain ◽  
Muhammed Hasnain Kabir Nayeem ◽  
Dr. Md Abu Taher Ali
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Mean Velocity ◽  
Potential Core ◽  
Swirling Jets ◽  
The Mean ◽  
Sinusoidal Flow

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

scholarly journals Effects of inlet velocity profiles for thermal stripping phenomena in T-junctions

2021 ◽  
Vol 2116 (1) ◽  
pp. 012026
Author(s):  
Lisa Lampunio ◽  
Yu Duan ◽  
Raad Issa ◽  
Matthew D. Eaton
Keyword(s):  
Velocity Profiles ◽  
Lower Sensitivity ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Inlet Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Domain ◽  
The Mean ◽  
Good Agreement

Abstract This paper investigates the effects of different inlet velocities on thermal stripping phenomena within a T-junction. The computational flow domain is modelled using the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model implemented within the commercial CFD code STAR-CCM+ 12.04. The computational model is validated against the OECD-NEA-Vattenfall T-junction Benchmark data. The influence of flat and fully developed inlet velocity profiles is then assessed. The results are in good agreement with the experimental data. The different inlet velocity profiles have a non-negligible effect on the mean wall temperature. The mean velocity shows lower sensitivity to changes in inlet velocity profiles, whose influence is confined mainly to the recirculation zone near the T-junction.

Scaling of Favorable Pressure Gradient Turbulent Boundary Layers With Eventual Relaminarization

2005 ◽  
Author(s):  
Rau´l Bayoa´n Cal ◽  
Xia Wang ◽  
Luciano Castillo
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Velocity Profiles ◽  
Turbulent Boundary Layers ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Favorable Pressure Gradient ◽  
The Mean

Applying similarity analysis to the RANS equations of motion for a pressure gradient turbulent boundary layer, Castillo and George [1] obtained the scalings for the mean deficit velocity and the Reynolds stresses. Following this analysis, Castillo and George studied favorable pressure gradient (FPG) turbulent boundary layers. They were able to obtain a single curve for FPG flows when scaling the mean deficit velocity profiles. In this study, FPG turbulent boundary layers are analyzed as well as relaminarized boundary layers subjected to an even stronger FPG. It is found that the mean deficit velocity profiles diminish when scaled using the Castillo and George [1] scaling, U∞, and the Zagarola and Smits [2] scaling, U∞δ*/δ. In addition, Reynolds stress data has been analyzed and it is found that the relaminarized boundary layer data decreases drastically in all components of the Reynolds stresses. Furthermore, it will be shown that the shape of the profile for the wall-normal and Reynolds shear stress components change drastically given the relaminarized state. Therefore, the mean velocity deficit profiles as well as Reynolds stresses are found to be necessary in order to understand not only FPG flows, but also relaminarized boundary layers.

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