Plane Turbulent Wall Jet Flow Development and Friction Factor

1963 ◽  
Vol 85 (1) ◽  
pp. 47-53 ◽  
Author(s):  
G. E. Myers ◽  
J. J. Schauer ◽  
R. H. Eustis
Keyword(s):  
Maximum Velocity ◽  
Velocity Profiles ◽  
Wall Jet ◽  
Shearing Stress ◽  
Integral Methods ◽  
Velocity Decay ◽  
Wall Jet Flow ◽  
Turbulent Wall ◽  
Momentum Integral ◽  
Wall Shearing Stress

An investigation of the jet development, the velocity profiles, and the wall shearing stress in a two-dimensional, incompressible, turbulent wall jet was undertaken. The maximum velocity decay, jet thickness, and the shearing stress are predicted analytically by momentum-integral methods. Experimental data concerning velocity profiles, velocity decay, and jet thickness agree well with previous investigators. The wall shearing stress was measured by a hot-film technique and the results help to resolve a wide divergence between the experimental values of other investigators.

Analysis of a Power Law and Log Law for a Turbulent Wall Jet Over a Transitional Rough Surface: Universal Relations

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Noor Afzal ◽  
Abu Seena
Keyword(s):  
Experimental Data ◽  
Rough Surface ◽  
Power Law ◽  
Power Laws ◽  
Velocity Profiles ◽  
Wall Jet ◽  
Log Law ◽  
Jet Velocity ◽  
Turbulent Wall ◽  
Momentum Integral

The power law and log law velocity profiles and an integral analysis in a turbulent wall jet over a transitional rough surface have been proposed. Based on open mean momentum Reynolds equations, a two layer theory for large Reynolds numbers is presented and the matching in the overlap region is carried out by the Izakson-Millikan-Kolmogorov hypothesis. The velocity profiles and skin friction are shown to be governed by universal log laws as well as by universal power laws, explicitly independent of surface roughness, having the same constants as a fully smooth surface wall jet (or fully rough surface wall jet, as appropriate). The novel scalings for stream-wise variations of the flow over a rough wall jet have been analyzed, and best fit relations for maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor, and momentum integral are supported by the experimental data. There is no universality of scalings in traditional variables, and different expressions are needed for transitional roughness. The experimental data provides very good support to our universal relations proposed in terms of alternate variables.

An Experimental Study of the Forcing Effect on the Flow and Heat Transfer in a Turbulent Wall Jet

2015 ◽  
Author(s):  
Johnny Issa ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Stream Flow ◽  
Free Stream ◽  
Maximum Velocity ◽  
Local Maximum ◽  
Jet Flow ◽  
Wall Jet ◽  
Wall Jet Flow ◽  
Turbulent Wall

The effect of the exit wall jet flow excitation on the flow and thermal behaviors of the turbulent wall jet is experimentally investigated. Various forcing amplitudes and frequencies are used in the presence and absence of a free stream flow. Forcing the flow showed to have a major impact on the fluid mechanics of the turbulent wall jet which was clearly shown in the velocity fields and the associated time-averaged quantities such as the wall jet spread and the maximum velocity decay. The normal direction at which the local maximum velocity occurs, also known as the wall jet spreading, is shown to move further away from the wall and is increased by more than 20% under some forcing conditions. The local maximum velocity decay with the downstream direction is reduced by more than 2.5% at further downstream locations. At a given location, the increase in the wall jet spreading together with the reduction in the mean velocity results in a decrease in the wall skin friction calculated using the slope of the mean velocity in the viscous sublayer, a behavior consistent with the literature. Due to its importance in enhancing heat transfer phenomena, the effect of the forcing on the streamwise velocity fluctuations is also investigated under the various forcing conditions. The profiles of the fluctuating component of the velocity, u’, are measured at various downstream locations since they are essential in understanding the growth of the disturbances. Forcing the wall jet increased u’ in the inner and outer regions and revealed the two peaks corresponding to the inner and outer shear layers respectively. This phenomenon is attributed to the added disturbance at the jet exit in addition to the disturbance growth with the downstream direction. The introduction of wall jet flow forcing at various amplitudes and frequencies showed a significant effect on the thermal behavior of the wall jet and was more pronounced in the absence of a free stream flow, a fact related to the evolution of the mixing layer with the downstream direction. In the absence of a free stream flow, Nusselt number decreases with increasing forcing amplitude and frequency in the region close to the jet exit. The decay of Nusselt number in the downstream direction showed an inflection point at further downstream locations which leads to a larger Nusselt number value than the one observed in the unforced case. This behavior is related to the enhanced mixing between the wall jet flow and the free stream due to forcing, which results in a reduction in the wall skin friction and consequently a decrease in the heat transfer rate from the wall.

The asymptotic downstream flow of plane turbulent wall jets without external stream

2015 ◽  
Vol 779 ◽  
pp. 351-370 ◽  
Author(s):  
Klaus Gersten
Keyword(s):  
Experimental Data ◽  
Momentum Flux ◽  
Maximum Velocity ◽  
Jet Flow ◽  
Plane Wall ◽  
Wall Jet ◽  
Free Jet ◽  
Wall Distance ◽  
Wall Jet Flow ◽  
Turbulent Wall

The plane turbulent wall-jet flow without externally imposed stream is considered. It is assumed that the wall jet does not emerge from a second wall perpendicular to the velocity vector of the initial wall jet. The (kinematic) momentum flux $K(x)$ of the wall jet decreases downstream owing to the shear stress at the wall. This investigation is based on the hypothesis that the total friction force on the wall is smaller than the total inflow momentum flux. In other words, the turbulent wall jet tends to a turbulent ‘half-free jet’ with a non-zero momentum flux $K_{\infty }\;(\text{m}^{3}~\text{s}^{-2})$ far downstream. The fact that the turbulent half-free jet is the asymptotic form of a turbulent wall jet is the basis for a singular perturbation method by which the wall-jet flow is determined. It turns out that the ratio between the wall distance $y_{m}$ of the maximum velocity and the wall distance $y_{0.5}$ of half the maximum velocity decreases downstream to zero. Dimensional analysis leads immediately to a universal function of the dimensionless momentum flux $K(\mathit{Re}_{x})/K_{\infty }$ that depends asymptotically only on the local Reynolds number $\mathit{Re}_{x}=\sqrt{(x-x_{0})K_{\infty }}/{\it\nu}$, where $x_{0}$ denotes the coordinate of the virtual origin. When the values $K$ and ${\it\nu}$ at the position $x-x_{0}$ are known, the asymptotic momentum flux $K_{\infty }$ can be determined. Experimental data on all turbulent plane wall jets (except those emerging from a second plane wall) collapse to a single universal curve. Comparisons between available experimental data and the analysis make the hypothesis $K_{\infty }\neq 0$ plausible. A convincing verification, however, will be possible in the future, preferably by direct numerical simulations.

Research on Turbulent Boundary Layer Development of Hydraulic Jump Region with the Theory of Plane Adhesive Wall Jet Flow

2012 ◽  
Vol 212-213 ◽  
pp. 1141-1146
Author(s):  
Zhi Chang Zhang ◽  
Ruo Bing Li ◽  
Ying Zhao ◽  
Ming Huan Fu
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Hydraulic Jump ◽  
Rectangular Channel ◽  
Jet Flow ◽  
Wall Jet ◽  
Boundary Layer Development ◽  
Wall Jet Flow ◽  
Momentum Integral ◽  
Layer Development

【Objective】The calculation of turbulent boundary layer development in hydraulic jump region is put forwarded.【Method】According to the analysis of predecessors’ researches about plane adhesive wall jet flow of rectangular channel, Based on the momentum integral equation of turbulent boundary layer and the velocity distribution formula of adhesive wall jet flow, turbulent boundary layer development of hydraulic jump region in rectangular channel is researched.【Result】Formulas of the development of boundary layer in hydraulic jump region and drag coefficient are obtained, the accuracy of equations are verified by the example. 【Conclusion】The calculation has enlightened effect on the hydraulic characteristics of hydraulic jump.

Parametric Analysis of Turbulent Wall Jet in Still Air Over a Transitional Rough, With Asymptotes of Fully Rough and Fully Smooth Wall Jets

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Noor Afzal ◽  
Abu Seena
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Rough Surfaces ◽  
Flow Direction ◽  
Wall Jet ◽  
Functional Forms ◽  
Jet Velocity ◽  
Turbulent Wall ◽  
Momentum Integral ◽  
Power Law Index

The novel scalings for streamwise variations of the flow in a turbulent wall jet over a fully smooth, transitional, and fully rough surfaces have been analyzed. The universal scaling for arbitrary wall roughness is considered in terms of the roughness friction Reynolds number (that arises from the stream wise variations of roughness in the flow direction) and roughness Reynolds number at the nozzle jet exit. The transitional rough wall jet functional forms have been proposed, whose numerical constants power law index and prefactor are estimated from best fit to the data for several variables, like, maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor and momentum integral, which are supported by the experimental data. The data shows that the two asymptotes of fully rough and fully smooth surfaces are co-linear with transitional rough surface, predicting same constants for any variable of flow for full smooth, fully rough and transitional rough surfaces. There is no universality of scalings in terms of traditional variables as different expressions are needed for each stage of the transitional roughness. The experimental data provides very good support to our universal relations.

A Comparison of Classic and Snapshot Proper Orthogonal Decomposition on the Three Dimensional Wall Jet Flow Field

2014 ◽  
Author(s):  
Mahdi Hosseinali ◽  
Stephen Wilkins ◽  
Lhendup Namgyal ◽  
Joseph Hall
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Energy Content ◽  
Near Field ◽  
Three Dimensional ◽  
Orthogonal Decomposition ◽  
Wall Jet ◽  
Polar Coordinate ◽  
Wall Jet Flow ◽  
Turbulent Wall ◽  
Proper Orthogonal

In this paper, classic Proper Orthogonal Decomposition (POD) on a polar coordinate and snapshot POD on a Cartesian grid will be applied separately in the near field of a turbulent wall jet. Three-component stereoscopic PIV measurements are performed in the transverse plane of a wall jet formed using a round contoured nozzle with a Reynolds number of 250,000. Eigenfunctions and energy distributions of the two methods are compared. Reconstructions using same number of modes and same content of energy have been compared. The effect of grid resolution on the energy content of the classic method has also been studied.

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.

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