Velocity distributions under floating covers

1982 ◽  
Vol 9 (1) ◽  
pp. 76-83 ◽  
Author(s):  
Y. L. Lau
Keyword(s):  
Turbulence Model ◽  
Maximum Velocity ◽  
Channel Flows ◽  
Flow Depth ◽  
Flow Properties ◽  
Mean Velocity ◽  
Bottom Boundary ◽  
Standard Procedures ◽  
Logarithmic Distribution ◽  
The Mean

The [Formula: see text] turbulence model has been used to calculate the velocity distributions for a large number of channel flows with different top and bottom boundary roughnesses. The resulting distributions are used to review the standard procedures for stream gauging of ice-covered flows. It is found that the average of the velocities at [Formula: see text] and [Formula: see text] of the depth is indeed very nearly equal to the overall mean velocity. Examination of the velocity profiles shows that the profiles deviate from the logarithmic distribution for about 40% of the flow depth. Other flow properties, such as the location of the maximum velocity and the mean velocities in the top and bottom layers, are also examined.

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.

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.

scholarly journals A study on the derivation of a mean velocity formula from Chiu's velocity formula and bottom shear stress

2011 ◽  
Vol 8 (4) ◽  
pp. 6419-6442 ◽  
Author(s):  
T. H. Choo ◽  
I. J. Jeong ◽  
S. K. Chae ◽  
H. C. Yoon ◽  
H. S. Son
Keyword(s):  
Shear Stress ◽  
Flow Rate ◽  
Estimation Method ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
River Bed ◽  
The Mean ◽  
Bed Slope ◽  
Discharge Estimation ◽  
Discrepancy Ratio

Abstract. This study proposed a new discharge estimation method using a mean velocity formula derived from Chiu's 2D velocity formula of probabilistic entropy concept and the river bed shear stress of channel. In particular, we could calculate the mean velocity, which is hardly measurable in flooding natural rivers, in consideration of several factors reflecting basic hydraulic characteristics such as river bed slope, wetted perimeter, width, and water level that are easily obtainable from rivers. In order to test the proposed method, we used highly reliable flow rate data measured in the field and published in SCI theses, estimated entropy M from the results of the mean velocity formula and, at the same time, calculated the maximum velocity. In particular, we obtained phi(M) expressing the overall equilibrium state of river through regression analysis between the maximum velocity and the mean velocity, and estimated the flow rate from the newly proposed mean velocity formula. The relation between estimated and measured discharge was analyzed through the discrepancy ratio, and the result showed that the estimate value was quite close to the measured data.

scholarly journals Vertical Distribution of Nearshore Flow Velocity

2016 ◽  
Vol 23 (s1) ◽  
pp. 104-108
Author(s):  
Li Chunhui ◽  
Fu Xiaoyan ◽  
Li Ruijie ◽  
Dai Lu ◽  
Chen Peng
Keyword(s):  
Vertical Distribution ◽  
Flow Velocity ◽  
Engineering Application ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
Basic Principles ◽  
Measured Flow ◽  
The Mean ◽  
New Formula ◽  
Distribution Of Flow

Abstract In this paper, a new exponential formed vertical distribution of nearshore flow velocity is constructed, which is simpler in form and more suitable for engineering application. The physical meaning of the new formula is more specific than that of Soulsby. Compared with those logarithmic formed ones, the new one does not need the maximum velocity and only needs the mean velocity in vertical, which gives it better engineering practicability. Apply the new formula to Jiangsu coastal area and compare the results with that of Soulsby whose results show the new formula agrees better with the measured flow velocity, which reasonably reflects the basic principles of vertical distribution of flow velocity.

The forced turbulent wall jet

1992 ◽  
Vol 242 ◽  
pp. 577-609 ◽  
Author(s):  
Y. Katz ◽  
E. Horev ◽  
I. Wygnanski
Keyword(s):  
Maximum Velocity ◽  
Wall Stress ◽  
Coherent Motion ◽  
Settling Chamber ◽  
Wall Jet ◽  
Appreciable Effect ◽  
External Excitation ◽  
Mean Velocity ◽  
The Mean ◽  
Turbulent Wall

The effects of external two-dimensional excitation on the plane turbulent wall jet were investigated experimentally and theoretically. Measurements of the streamwise component of velocity were made throughout the flow field for a variety of imposed frequencies and amplitudes. The present data were always compared to the results generated in the absence of external excitation. Two methods of forcing were used: one global, imposed on the entire jet by pressure fluctuations in the settling chamber and one local, imposed on the shear layer by a small flap attached to the outer nozzle lip. The fully developed wall jet was shown to be insensitive to the method of excitation. Furthermore, external excitation has no appreciable effect on the rate of spread of the jet nor on the decay of its maximum velocity. In fact the mean velocity distribution did not appear to be altered by the external excitation in any obvious manner. The flow near the surface, however, (i.e. for 0 < Y+ < 100) was profoundly different from the unforced flow, indicating a reduction in wall stress exceeding at times 30%. The production of turbulent energy near the surface was also reduced, lowering the intensities of the velocity fluctuations. External excitation enhanced the two-dimensionality and the periodicity of the coherent motion. Spectral analysis and flow visualization suggested that the large coherent structures in this flow might be identified with the most-amplified primary instability modes of the mean velocity profile. Detailed stability analysis confirmed this proposition though not at the same level of accuracy as it did in many free shear flows.

scholarly journals The Role of Forcing and Eddy Viscosity Variation on the Log-Layer Mismatch Observed in Wall-Modeled Large-Eddy Simulations

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Rey DeLeon ◽  
Inanc Senocak
Keyword(s):  
Flow Rate ◽  
Eddy Viscosity ◽  
Degree Of Freedom ◽  
Channel Flows ◽  
Momentum Balance ◽  
Mean Velocity ◽  
Turbulent Channel Flows ◽  
The Mean ◽  
Viscosity Variation

We investigate the role of eddy viscosity variation and the effect of zonal enforcement of the mass flow rate on the log-layer mismatch problem observed in turbulent channel flows. An analysis of the mean momentum balance shows that it lacks a degree-of-freedom (DOF) when eddy viscosity is large, and the mean velocity conforms to an incorrect profile. Zonal enforcement of the target flow rate introduces an additional degree-of-freedom to the mean momentum balance, similar to an external stochastic forcing term, leading to a significant reduction in the log-layer mismatch. We simulate turbulent channel flows at friction Reynolds numbers of 2000 and 5200 on coarse meshes that do not resolve the viscous sublayer. The second-order turbulence statistics agree well with the direct numerical simulation benchmark data when results are normalized by the velocity scale extracted from the filtered velocity field. Zonal enforcement of the flow rate also led to significant improvements in skin friction coefficients.

Validity and reliability of the WIMU® system to measure barbell velocity during the half-squat exercise

2019 ◽  
Vol 233 (3) ◽  
pp. 408-415 ◽  
Author(s):  
Felipe García-Pinillos ◽  
Pedro A Latorre-Román ◽  
Fernando Valdivieso-Ruano ◽  
Carlos Balsalobre-Fernández ◽  
Juan A Párraga-Montilla
Keyword(s):  
Gold Standard ◽  
Concurrent Validity ◽  
Pearson Correlation ◽  
Maximum Velocity ◽  
Systematic Bias ◽  
Loading Test ◽  
Mean Velocity ◽  
Velocity Relationship ◽  
Squat Exercise ◽  
The Mean

This study aimed at determining the reliability and concurrent validity of the WIMU® system when measuring barbell velocity during the half-squat exercise by comparing data with the gold standard. A total of 19 male competitive powerlifters performed an incremental loading test using the half-squat exercise. The mean velocity, mean propulsive velocity and maximum velocity of all repetitions were recorded through both WIMU and T-Force systems. As a measure of reliability, coefficient of variations ranged from 6%–17% and standard error of means ranged from 0.02–0.11 m/s, showing very close reliability of data from both devices. Validity, in terms of coefficient of correlations and pairwise comparisons, was also tested. Except for some relative loads, the Pearson correlation analysis revealed significant correlations between both devices for mean velocity, mean propulsive velocity and maximum velocity (r > 0.6, p < 0.05). The mean velocity, mean propulsive velocity and maximum velocity were underestimated for the WIMU system compared to T-Force data at some points of the load–velocity relationship. The linear regression models performed revealed a strong load–velocity relationship in the half-squat exercise for each individual using mean velocity, mean propulsive velocity and maximum velocity, regardless of the instrument used (R2 > 0.77 in all cases). Bland–Altman plots revealed low systematic bias (≤0.06 m s−1) and random error (≤0.07 m s−1) for the mean velocity and mean propulsive velocity obtained from the WIMU system as compared to the T-Force, while the maximum velocity resulted in an underestimation by the WIMU system (–0.16 m s−1) as compared to the linear position transducer system. The results indicate that the WIMU system is a reliable tool for tracking barbell velocity in the half squat, but these data also reveal some limitations regarding its concurrent validity as compared to the gold standard, with velocity measures slightly underestimated in the tested conditions.

Large eddy simulation of a stratified boundary layer under an oscillatory current

2009 ◽  
Vol 643 ◽  
pp. 233-266 ◽  
Author(s):  
BISHAKHDATTA GAYEN ◽  
SUTANU SARKAR ◽  
JOHN R. TAYLOR
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Mixed Layer ◽  
Numerical Study ◽  
Bottom Boundary Layer ◽  
Mean Velocity ◽  
Bottom Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean

A numerical study based on large eddy simulation is performed to investigate a bottom boundary layer under an oscillating tidal current. The focus is on the boundary layer response to an external stratification. The thermal field shows a mixed layer that is separated from the external stratified fluid by a thermocline. The mixed layer grows slowly in time with an oscillatory modulation by the tidal flow. Stratification strongly affects the mean velocity profiles, boundary layer thickness and turbulence levels in the outer region although the effect on the near-bottom unstratified fluid is relatively mild. The turbulence is asymmetric between the accelerating and decelerating stages. The asymmetry is more pronounced with increasing stratification. There is an overshoot of the mean velocity in the outer layer; this jet is linked to the phase asymmetry of the Reynolds shear stress gradient by using the simulation data to examine the mean momentum equation. Depending on the height above the bottom, there is a lag of the maximum turbulent kinetic energy, dissipation and production with respect to the peak external velocity and the value of the lag is found to be influenced by the stratification. Flow instabilities and turbulence in the bottom boundary layer excite internal gravity waves that propagate away into the ambient. Unlike the steady case, the phase lines of the internal waves change direction during the tidal cycle and also from near to far field. The frequency spectrum of the propagating wave field is analysed and found to span a narrow band of frequencies clustered around 45°.

Computational Analysis of Various Factors on the Edgetone Mechanism Using High Order Schemes

2005 ◽  
Author(s):  
Taku Nonomura ◽  
Hiroko Muranaka ◽  
Kozo Fujii
Keyword(s):  
Acoustic Waves ◽  
Feedback Loop ◽  
Stokes Equations ◽  
Computational Study ◽  
Maximum Velocity ◽  
Mean Velocity ◽  
Good Correspondence ◽  
The Past ◽  
The Mean ◽  
Jet Velocity

Flow fields of two dimensional jets impinging on the sharp edge are computationally simulated and the effect of various parameters on the edgetone that is created by the flow interaction is investigated. Compressible Navier-Stokes equations are used so that acoustic waves are captured accurately as a part of feedback-loop. For numerical accuracy, Pade type compact finite difference scheme are used. First parameter is the jet velocity. Computational result shows good qualitative agreement with the experiment. Edgetone frequencies obtained by the computation also show good correspondence with those of experimental study in the past. Second parameter is the nozzle lip thickness. Although not considered in the computational study in the past, the nozzle lip thickness influences to the results. Amplitude of acoustics of larger nozzle lip is greater than that of smaller ones. This effect may comes from the fact that acoustic wave as a part of feedback loop is emphasized by nozzle lip. Third parameter is the jet-profile. Four different jet-profiles with the same maximum velocity (from top-hat profile to parabolic profile) and four different jet-profiles with the same mean velocity are computed. The mean jet velocity appears to have strong influence on the stage. The results also indicated that the mean jet velocity and the jet-profile have influence on edgetone frequencies.

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