Convection Velocity of Temperature Fluctuations in a Turbulent Flume

2004 ◽  
Vol 126 (5) ◽  
pp. 843-848 ◽  
Author(s):  
G. Hetsroni ◽  
I. Tiselj and ◽  
R. Bergant ◽  
A. Mosyak and ◽  
E. Pogrebnyak
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Temperature Field ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Velocity Fluctuation ◽  
Temperature Fluctuations ◽  
Scale Dependence ◽  
Convection Velocity ◽  
Wall Boundary Condition

A numerical investigation of the temperature field in a turbulent flume is presented. We consider the effect of the Prandtl number on the convection velocity of temperature fluctuations in a turbulent boundary layer, and focus also on the effect of the Prandtl number on the connection between the velocity and the temperature fluctuations. Close to the wall, y+<2, convection velocities of the temperature fluctuations decrease with an increase in the Prandtl number, i.e., the scale dependence becomes significantly important. In the region y+<2 the relation of the convection velocity of the temperature fluctuation to that of the velocity fluctuation may be expressed as UcT+=Ucu+Pr−1/3 and Ucq+=Ucu+Pr−1/2 for isothermal and isoflux wall boundary condition, respectively.

Lattice Boltzmann Study of Flow and Temperature Structures ofNon-Isothermal Laminar Impinging Streams

2013 ◽  
Vol 13 (3) ◽  
pp. 835-850 ◽  
Author(s):  
Wenhuan Zhang ◽  
Zhenhua Chai ◽  
Zhaoli Guo ◽  
Baochang Shi
Keyword(s):  
Boundary Condition ◽  
Reynolds Number ◽  
Temperature Field ◽  
Prandtl Number ◽  
Lattice Boltzmann ◽  
Periodic Structures ◽  
Temperature Fields ◽  
Buoyancy Effect ◽  
Practical Applications ◽  
Boltzmann Method

AbstractPrevious works on impinging streams mainly focused on the structures of flow field, but paid less attention to the structures of temperature field, which are very important in practical applications. In this paper, the influences of the Reynolds number (Re) and Prandtl number (Pr) on the structures of flow and temperature fields of non-isothermal laminar impinging streams are both studied numerically with the lattice Boltzmann method, and two cases with and without buoyancy effect are considered. Numerical results show that the structures are quite different in these cases. Moreover, in the case with buoyancy effect, some new deflection and periodic structures are found, and their independence on the outlet boundary condition is also verified. These findings may help to understand the flow and temperature structures of non-isothermal impinging streams further.

Wall Pressure Phase Velocity Measurements in a Turbulent Boundary Layer

2012 ◽  
Author(s):  
Teresa S. Miller ◽  
Mark J. Moeller
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Phase Velocity ◽  
Group Velocity ◽  
Noise Source ◽  
Wall Pressure ◽  
Interior Noise ◽  
Convection Velocity ◽  
Phase Velocities ◽  
Wall Pressure Fluctuation

The turbulent boundary layer that forms on the outer surfaces of vehicles can be a significant source of interior noise. In automobiles this is known as wind noise, and at high speeds it dominates the interior noise. For airplanes the turbulent boundary is also a dominant noise source. Because of its importance as a noise source, it is desirable to have a model of the turbulent wall pressure fluctuations for interior noise prediction. One important parameter in building the wall pressure fluctuation model is the convection velocity. In this paper, the phase velocity was determined from the streamwise pressure measurements. The phase velocity was calculated for three separation distances ranging from 0.25 to 1.30 boundary layer thicknesses. These measurements were made for a Mach number range of 0.1 < M < 0.6. The phase velocity was shown to vary with sensor spacing and frequency. The data collapsed well on outer variable normalization. The phase velocities were fit and the group velocity was calculated from the curve fit. The group velocity was consistent with the array measured convection velocities. The group velocity was also estimated by a band limited cross correlation technique that used the Hilbert transform to find the energy delay. This result was consistent with the group velocity inferred from the phase velocities and the array measured convection velocity. From this research, it is suggested that the group velocity found in this study should be used to estimate the convection velocity in wall pressure fluctuation models.

Wall Temperature and Prandtl Number Effects on Turbulent Boundary Layer Thicknesses and Shape Factors for Subsonic Compressible Gas Flow Over a Flat Plate

1969 ◽  
Author(s):  
W. J. Kelnhofer
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Flat Plate ◽  
Wall Temperature ◽  
Gas Flow ◽  
Density Variation ◽  
Shape Factors ◽  
Heating And Cooling ◽  
Subsonic Gas Flow

Based on n-power velocity and temperature profiles a method of computing various turbulent boundary layer thicknesses and shape factors affected by wall temperature and Prandtl number for fully developed subsonic gas flow over a flat plate is presented. Density variation in the boundary layer is given main consideration. Numerical computations include both heating and cooling of gas. Boundary layer thicknesses and shape factors are shown to be significantly affected by wall temperature and to a lesser degree by Prandtl number. An experiment is described which involved air flow up to 30 m/sec over a flat plate maintained at constant wall temperatures up to 250 C. Comparisons between theory and experiment are good.

Paradoxes of Heat Transfer on a Permeable Wall

2010 ◽  
Author(s):  
A. I. Leontiev ◽  
V. G. Lushchik ◽  
A. E. Yakubenko
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Numerical Modeling ◽  
Turbulent Boundary Layer ◽  
Prandtl Number ◽  
Wall Temperature ◽  
Gas Injection ◽  
Gas Mixtures ◽  
Permeable Wall ◽  
Gas Temperature

Numerical modeling of a turbulent boundary layer on a permeable wall with gas injection is performed. New effects are discovered. It is shown in particular that the wall temperature in the region of the gas film may be lower than the injected gas temperature. This effect is especially essential for gas mixtures with low values of the Prandtl number.

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