Simultaneous measurements of velocity and temperature fluctuations in thermal boundary layer in a drag-reducing surfactant solution flow

The heat transport phenomena in a developed thermal boundary layer of surfactant solution flow were investigated experimentally. The experiment was conducted under different surfactant additive concentrations. The temperature fluctuations in a thermal boundary layer in a smooth channel flow were measured by fine-wire thermocouple probe. Heat transfer reducing rate and temperature fluctuation characteristics including mean temperature distribution, intensity, wave form, spectral density function, and skewness factor were studied. The results showed that the turbulent transport is obstructed by additives, and the temperature field shows dramatic changes. High frequency component of temperature fluctuation of surfactant solution flow was decreased due to suppression of turbulence and viscoelasticity. Large temperature fluctuations occur in the thermal boundary layer because the development of the thermal boundary layer is obstructed, and large temperature fluctuations appear to concentrate the temperature gradient in the near-wall region (10 < y+ < 60). In contrast, viscous sublayer expands due to viscoelasticity, and the temperature gradient and turbulence fluctuation are small in the near-wall region of y+ < 10. As a result, two layers having significantly different characteristics seem to coexist. The heat transfer reduction is constant with variation of additive concentration condition, but heat transport phenomena were microscopically influenced by viscoelasticity.

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Statistical Analysis of Turbulent Heat Flux in a Thermal Boundary Layer of Drag-Reducing Surfactant Solution Flow

The Proceedings of the Thermal Engineering Conference ◽

10.1299/jsmeted.2003.421 ◽

2003 ◽

Vol 2003 (0) ◽

pp. 421-422

Author(s):

Feng Chen LI ◽

Yasuo KAWAGUCHI ◽

Koichi HISHIDA

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Statistical Analysis ◽

Thermal Boundary Layer ◽

Surfactant Solution ◽

Turbulent Heat Flux ◽

Turbulent Heat ◽

Solution Flow

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On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient

Journal of Turbomachinery ◽

10.1115/1.2218520 ◽

2005 ◽

Vol 128 (4) ◽

pp. 689-698 ◽

Cited By ~ 9

Author(s):

T. P. Chong ◽

S. Zhong

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Pressure Gradient ◽

Velocity Component ◽

Thermal Boundary Layer ◽

Temperature Fluctuations ◽

Turbulent Spots ◽

Zone Length ◽

Favorable Pressure Gradient ◽

The Difference

This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favorable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity component U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations, and the second moment turbulent quantities are discussed and the influence of favorable pressure gradient on these parameters is examined. When a favorable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations and Reynolds shear stress occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (and turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study indicate that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favorable pressure gradient. This phenomenon is expected to slow down the development of a transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.

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Study on Thermal Boundary Layer in a Drag-Reducing Channel Flow by Surfactant Additives : Simultaneous Measurement of Velocity and Temperature Fluctuations

Proceedings of thermal engineering conference ◽

10.1299/jsmeptec.2002.0_113 ◽

2002 ◽

Vol 2002 (0) ◽

pp. 113-114

Author(s):

FengChen LI ◽

Yasuo KAWAGUCHI ◽

Koichi HISHIDA

Keyword(s):

Boundary Layer ◽

Channel Flow ◽

Simultaneous Measurement ◽

Thermal Boundary Layer ◽

Temperature Fluctuations

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Fine-scale statistics of temperature and its derivatives in convective turbulence

Journal of Fluid Mechanics ◽

10.1017/s0022112008002954 ◽

2008 ◽

Vol 611 ◽

pp. 13-34 ◽

Cited By ~ 58

Author(s):

M. S. EMRAN ◽

J. SCHUMACHER

Keyword(s):

Boundary Layer ◽

Probability Density Function ◽

Rayleigh Number ◽

Probability Density ◽

Density Function ◽

Dissipation Rate ◽

Thermal Boundary Layer ◽

Temperature Fluctuations ◽

Thermal Dissipation ◽

Fine Scale

We study the fine-scale statistics of temperature and its derivatives in turbulent Rayleigh–Bénard convection. Direct numerical simulations are carried out in a cylindrical cell with unit aspect ratio filled with a fluid with Prandtl number equal to 0.7 for Rayleigh numbers between 107 and 109. The probability density function of the temperature or its fluctuations is found to be always non-Gaussian. The asymmetry and strength of deviations from the Gaussian distribution are quantified as a function of the cell height. The deviations of the temperature fluctuations from the local isotropy, as measured by the skewness of the vertical derivative of the temperature fluctuations, decrease in the bulk, but increase in the thermal boundary layer for growing Rayleigh number, respectively. Similarly to the passive scalar mixing, the probability density function of the thermal dissipation rate deviates significantly from a log-normal distribution. The distribution is fitted well by a stretched exponential form. The tails become more extended with increasing Rayleigh number which displays an increasing degree of small-scale intermittency of the thermal dissipation field for both the bulk and the thermal boundary layer. We find that the thermal dissipation rate due to the temperature fluctuations is not only dominant in the bulk of the convection cell, but also yields a significant contribution to the total thermal dissipation in the thermal boundary layer. This is in contrast to the ansatz used in scaling theories and can explain the differences in the scaling of the total thermal dissipation rate with respect to the Rayleigh number.

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On the Momentum and Thermal Structures of Turbulent Spots in a Favourable Pressure Gradient

Volume 3: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-69046 ◽

2005 ◽

Author(s):

T. P. Chong ◽

S. Zhong

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Pressure Gradient ◽

Thermal Boundary Layer ◽

Turbine Blades ◽

Temperature Fluctuations ◽

Turbulent Heat ◽

Turbulent Spots ◽

Zone Length ◽

The Difference

This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favourable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations and the second moment turbulent quantities are discussed and the influence of favourable pressure gradient on these parameters is examined. When a favourable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations (or Reynolds shear stress) occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (or turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study show that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favourable pressure gradient. This phenomenon is expected to slow down the spanwise growth of turbulent spots in the transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.

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