Wave Force Coefficient Correlation Based on Wake Volume Scaling

1994 ◽  
Vol 116 (2) ◽  
pp. 97-101
Author(s):  
T. E. Horton ◽  
M. J. Feifarek ◽  
H. Golestanian
Keyword(s):  
Boundary Layer ◽  
Dimensionless Parameter ◽  
Wave Force ◽  
Hydrodynamic Drag ◽  
Half Cycle ◽  
Square Root ◽  
Force Coefficient ◽  
Coefficient Corrélation ◽  
Flow Through ◽  
Flow Drag

A correlation of the hydrodynamic drag force on a cylinder for a periodic motion is demonstrated. The correlation indicates the dependance of the unsteady flow drag coefficient on the wake volume parameter. This parameter is a measure of the volume of flow through the boundary layer and into the wake in a half-cycle. For a laminar boundary layer, this dimensionless parameter is proportional to the Keulegan-Carpenter number and inversely proportional to the square root of the Reynolds number. Using wake volume scaling, drag coefficients were effectively collapsed into a single curve.

On Wave Force Coefficient Variability

1987 ◽  
Vol 109 (4) ◽  
pp. 295-306 ◽  
Author(s):  
J. H. Nath
Keyword(s):  
Phase Angle ◽  
Vortex Shedding ◽  
Vertical Cylinder ◽  
Wave Force ◽  
Maximum Force ◽  
Periodic Waves ◽  
Force Coefficient ◽  
Ambient Flow ◽  
Smooth Cylinder ◽  
Phase Differences

Wave force coefficient variability for cylinders, from wave to wave in a train of periodic waves, has been shown to be dependent on the phase of the force record relative to the ambient flow. The phase varies due to vortex shedding, but the maximum force is approximately constant as seen from this work and the work of other investigators. Thus, the maximum force coefficient is tightly organized according to the Keulegan-Carpenter number and scatter is seen in the phase angle versus Keulegan-Carpenter number. On the other hand, both Cd and Cm have scatter due to these phase differences from wave to wave. For unknown reasons, even when averaged over several wave cycles there is scatter in the results for Cd and Cm. This investigation shows that the maximum force coefficients for a heavily roughened vertical cylinder are tightly arranged according to the Keulegan-Carpenter number and the period parameter. Furthermore, the phase angle is similarly much more organized than for the smooth cylinder.

Wall Boundary Layers in Turbomachines

1972 ◽  
Vol 14 (6) ◽  
pp. 411-423 ◽  
Author(s):  
H. Marsh ◽  
J. H. Horlock
Keyword(s):  
Boundary Layer ◽  
Integral Equations ◽  
Cross Flow ◽  
Inlet Guide Vanes ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Alternative Approach ◽  
Flow Through ◽  
The Many ◽  
Momentum Integral

Equations for the passage-averaged flow in a cascade are used to derive the momentum integral equations governing the development of the wall boundary layer in turbomachines. Several existing methods of analysis are discussed and an alternative approach is given which is based on the passage-averaged momentum integral equations. The analysis leads to an anomaly in the prediction of the cross flow and to avoid this it is suggested that for the many-bladed cascade there should be a variation of the blade force through the boundary layer. This variation of the blade force can be included in the analysis as a force deficit integral. The growth of the wall boundary layer has been calculated by four methods and the predictions are compared with two sets of published experimental results for flow through inlet guide vanes.

scholarly journals Sonic Eddy Model of the Turbulent Boundary Layer

Fluids ◽  
2022 ◽  
Vol 7 (1) ◽  
pp. 37
Author(s):  
Paul Dintilhac ◽  
Robert Breidenthal
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Entrainment Rate ◽  
Square Root ◽  
Reynolds Stresses ◽  
Free Shear Layer ◽  
Velocity Fluctuations ◽  
Acoustic Signaling

The effects of Mach number on the skin friction and velocity fluctuations of the turbulent boundary layer are considered through a sonic eddy model. Originally proposed for free shear flows, the model assumes that the eddies responsible for momentum transfer have a rotation Mach number of unity, with the entrainment rate limited by acoustic signaling. Under this assumption, the model predicts that the skin friction coefficient should go as the inverse Mach number in a regime where the Mach number is larger than unity but smaller than the square root of the Reynolds number. The velocity fluctuations normalized by the friction velocity should be the inverse square root of the Mach number in the same regime. Turbulent transport is controlled by acoustic signaling. The density field adjusts itself such that the Reynolds stresses correspond to the momentum transport. In contrast, the conventional van Driest–Morkovin view is that the Mach number effects are due to density variations directly. A new experiment or simulation is proposed to test this model using different gases in an incompressible boundary layer, following the example of Brown and Roshko in the free shear layer.

scholarly journals Turbulence statistics in smooth wall oscillatory boundary layer flow

2018 ◽  
Vol 849 ◽  
pp. 192-230 ◽  
Author(s):  
Dominic A. van der A ◽  
Pietro Scandura ◽  
Tom O’Donoghue
Keyword(s):  
Boundary Layer ◽  
Normal Distribution ◽  
Boundary Layer Flow ◽  
Vertical Gradient ◽  
Streamwise Velocity ◽  
Normal Velocity ◽  
Half Cycle ◽  
Velocity Fluctuations ◽  
Oscillatory Boundary Layer ◽  
Layer Flow

Turbulence characteristics of an asymmetric oscillatory boundary layer flow are analysed through two-component laser-Doppler measurements carried out in a large oscillatory flow tunnel and direct numerical simulation (DNS). Five different Reynolds numbers, $R_{\unicode[STIX]{x1D6FF}}$, in the range 846–2057 have been investigated experimentally, where $R_{\unicode[STIX]{x1D6FF}}=\tilde{u} _{0max}\unicode[STIX]{x1D6FF}/\unicode[STIX]{x1D708}$ with $\tilde{u} _{0max}$ the maximum oscillatory velocity in the irrotational region, $\unicode[STIX]{x1D6FF}$ the Stokes length and $\unicode[STIX]{x1D708}$ the fluid kinematic viscosity. DNS has been carried out for the lowest three $R_{\unicode[STIX]{x1D6FF}}$ equal to 846, 1155 and 1475. Both experimental and numerical results show that the flow statistics increase during accelerating phases of the flow and especially at times of transition to turbulent flow. Once turbulence is fully developed, the near-wall statistics remain almost constant until the late half-cycle, with values close to those reported for steady wall-bounded flows. The higher-order statistics reach large values within a normalized wall distance of approximately $y/\unicode[STIX]{x1D6FF}=0.2$ at phases corresponding to the onset of low-speed streak breaking, because of the intermittency of the velocity fluctuations at these times. In particular, the flatness of the streamwise velocity fluctuations reaches values of the order of ten, while the flatness of the wall-normal velocity fluctuations reaches values of several hundreds. Far from the wall, at locations where the vertical gradient of the streamwise velocity is zero, the skewness is approximately zero and the flatness is approximately equal to 3, representative of a normal distribution. At lower elevations the distribution of the fluctuations deviate substantially from a normal distribution, but are found to be well described by other standard theoretical probability distributions.

The Removal of the Boundary Layer of a Supersonic Flow by Means of a Slot

1963 ◽  
Vol 30 (2) ◽  
pp. 275-278
Author(s):  
M. Cloutier
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Static Pressure ◽  
Free Stream ◽  
Subsequent Development ◽  
Displacement Thickness ◽  
Free Stream Mach Number ◽  
Slot Opening ◽  
Flow Through ◽  
Transverse Slot

The influence of slot opening and of suction pressure upon the mass flow through the slot and the subsequent development of the boundary layer has been studied for the case of a single transverse slot opening into a boundary layer with a displacement thickness of 0.168 in. at a free-stream Mach number of 2.92. The results show that as much as 85 percent of the mass flow in the boundary layer between the wall and the position of the slot lip enters the slot, and that this result is independent of the slot reservoir pressure, providing the latter is less than approximately twice the tunnel static pressure.

Numerical Simulation of Evaporating Two-Phase Flow in a High-Aspect-Ratio Microchannel with Bends

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Junsik Lee ◽  
Junsub Kim ◽  
Hyungsoo Lim ◽  
Je Sung Bang ◽  
Jeong Min Seo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Film Cooling ◽  
High Speed ◽  
National Research Council ◽  
Air Cooling ◽  
Hole Size ◽  
High Efficient ◽  
Flow Through ◽  
Effusion Hole

Effusion cooling is one of the attractive methods for next generation high-efficient gas turbine which has a very hot gas temperature above 1,600oC. For higher effectiveness of the air cooling, the air-cooled flow through effusion-holes does not penetrate into the mainstream flow but still remains within freestream boundary layer. So the air-cooled surface temperature maintains at relatively lower than film cooling. Effusion cooling is generally known as operating in small effusion-hole size which is less than 0.2 mm. This study is intended to examine optimum effusion-hole size of the microscale effusion cooling through flow visualization. The air flow through effusion-holes is visualized using an oil atomizer, a DSPP laser-sheet illumination, and a high-speed CCD imaging. The visualized results show flow patterns and characteristics with different blowing ratio, BR = ρcUc / ρ∞U∞, (BR = 0.17 and 0.53) and effusion-hole size (D = 0.2 mm, 0.5 mm and 1.0 mm). The flow visualization condition is fixed at the mainstream Reynolds number of 10,000 and hole-to-hole spacing of 4 (S/D = 4). For larger effusion-hole of 1.0 mm [(a) and (b)], the effusion flow can penetrate into boundary layer which exhibits a film cooling. However the effusion flow is observed to be remained within boundary layer which shows an effusion cooling for smaller effusion-hole of 0.2 mm [(e) and (f)]. In case of (c) and (d), a series of vortical structure is also observed to be within the boundary layer along the effusion flat plate. Note that the effusion-hole size of 0.5 mm can be a candidate for making effusion cooling possible. [This work was supported by National Research Council of Science and Technology (NST) grant funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No. KIMM-NK203B).]

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