scholarly journals An attempt to measure fluctuating local pressure in free turbulent flow in water

2014 ◽  
Vol 9 (2) ◽  
pp. JFST0014-JFST0014 ◽  
Author(s):  
Takuya KAWATA ◽  
Hoshito MAEDA ◽  
Shinnosuke OBI
Keyword(s):  
Turbulent Flow ◽  
Local Pressure ◽  
Free Turbulent Flow

Excitation of internal waves by a turbulent boundary layer

1965 ◽  
Vol 22 (2) ◽  
pp. 241-252 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Wave Energy ◽  
Model Atmosphere ◽  
Convection Velocity ◽  
Surface Boundary ◽  
Wave Groups ◽  
Surface Boundary Layer ◽  
Barotropic Fluid ◽  
Free Turbulent Flow

In a barotropic fluid, a free turbulent flow induces a fluctuating potential flow which is determined by the instantaneous flow near the edge of the turbulent flow. If the surrounding fluid is stably stratified, internal wave-motions are possible and, in general, wave-energy accumulates until it is sufficient to modify the turbulent flow. Here the growth of wave-motion from rest is examined with particular reference to the atmospheric problem of wave excitation by the surface boundary layer. Wind shear is supposed negligible outside the turbulent flow and the disturbances from the boundary layer are assumed to travel with a convection velocity V relative to the upper air. For times large compared with {−g/ρ(dρ/dz)}−½ (ρ is the potential density), most of the wave-energy resides in components of phase-velocity near the convection velocity. For a model atmosphere with increased stability above a tropopause, this resonance mechanism leads to the formation of wave-groups with crests at right-angles to the convection velocity and wavelengths near 2πV[−g/ρ(dρ/dz)]−½. Using likely values for the surface disturbances, wave-amplitudes of order 100 m can develop within several hours of the initiation of the boundary layer but sufficient amplitude to produce overturning or breaking is unlikely within a reasonable time.

Effect of Triangular Roughness Elements on Pressure Drop and Laminar-Turbulent Transition in Microchannels and Minichannels

2006 ◽  
Author(s):  
Timothy P. Brackbill ◽  
Satish G. Kandlikar
Keyword(s):  
Turbulent Flow ◽  
Reynolds Numbers ◽  
Subject Area ◽  
Internal Flows ◽  
Local Pressure ◽  
Flow Area ◽  
Friction Factors ◽  
Roughness Elements ◽  
Initial Work ◽  
Constricted Flow

Roughness elements affect internal flows in different ways. One effect is a transition from laminar to turbulent flow at a lower Reynolds number than the predicted Re = 2300. Initial work at RIT in the subject area was performed by Schmitt and Kandlikar (2005) and Kandlikar et al. (2005), and this study is an extension of these efforts. The channel used in this study is rectangular, with varying separation between walls that have machined roughness elements. The roughness elements are saw-tooth in structure, with element heights of 107 and 117 μm for two pitches of 405 μm and 815 μm respectively. The resulting hydraulic diameters and Reynolds numbers based on the constricted flow area range from 424 μm to 2016 μm and 210 to 2400 respectively. Pressure measurements are taken at sixteen locations along the flow length of 88.9 mm to determine the local pressure gradients. The results for friction factors and transition to turbulent flow are obtained and compared with the data reported by Schmitt and Kandlikar (2005). The roughness elements cause an early transition to turbulent flow, and the friction factors in the laminar region are predicted accurately using the hydraulic diameter based on the constricted flow area.

Free Turbulent Flow

2010 ◽  
pp. 327-356
Author(s):  
Meinhard T. Schobeiri
Keyword(s):  
Turbulent Flow ◽  
Free Turbulent Flow

Prediction of Developing Turbulent Flow in a 90° Curved Duct Using Linear and Nonlinear Low-Re k-ε Models

Volume 1 ◽  
2004 ◽  
Author(s):  
M. Raisee ◽  
H. Alemi ◽  
H. Iacovides
Keyword(s):  
Turbulent Flow ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Main Stream ◽  
Local Pressure ◽  
Flow Measurements ◽  
Numerical Predictions ◽  
Flow Development ◽  
Curved Section

This paper reports the outcome of applying two different low-Re number eddy-viscosity models to resolve the complex three-dimensional motion that arises in turbulent flow in a square cross-section duct passing around a 90° bend. Flow computations have been obtained using a three-dimensional, non-orthogonal flow solver. For modeling of turbulence, the Launder and Sharma low-Re k–ε model and a recently modified version of nonlinear low-Re k–ε model that have been shown to be suitable for flow and thermal predictions in re-circulating and impinging jet flows, have been employed. A bounded version of the QUICK scheme was used for the approximation of convection in all transport equations. The numerical predictions are validated through comparisons with the reported flow measurements and are used to explain how the curvature influences the flow development. The results of the present investigation indicate that the curvature induces a strong secondary flow in the curved section of the duct. The secondary motion also persists downstream of the bend, although it slowly disappears with the main stream development. At the entrance of the curved section, the curvature alters the flow development by displacing the fluid towards the convex (inner) wall. Comparisons of the predicted stream-wise and cross-stream velocity components with the measured data indicate that both turbulence models employed in the present study can produce reasonable predictions, although the non-linear model predictions are generally closer to the measurements. Both turbulence models successfully reproduce the distribution as well as the levels of the local pressure coefficient in the curved section of the duct.

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