Calibration of a Heat Flux Gage for Skin Friction Measurement

Ramaprian, B. R.; Tu, S. W.

doi:10.1115/1.3241028

Cited by 7 publications

(4 citation statements)

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“…Brown 1967 , since the response of the hot film in a turbulent flow is not necessarily identical to that in a laminar flow with the same shear stress. Moreover, it is difficult to obtain a laminar flow for the calibration experiment, especially one that can cover the range of shear-stress values expected in an actual turbulent-flow application (Ramaprian & Tu 1983). This is particularly true for the high unit Reynolds number boundary layers of interest here.…”

Section: Skin-friction Probe Calibration Proceduresmentioning

confidence: 99%

Measurements of local skin friction in a microbubble-modified turbulent boundary layer

1985

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Local skin-friction reductions have been measured using an array of flush-mounted hot-film probes in a microbubble-modified, zero-pressure-gradient, turbulent bounddary layer. The results of earlier integrated skin-friction measurements, that showed the reduction to be a function of plate orientation, gas-flow rate and free-stream velocity, have been confirmed both qualitatively and quantitatively. With the measurement plate oriented so that buoyancy keeps the bubbles in boundary layer, it is shown that skin friction is reduced monotonically for all air-flow rates at each of three free-stream velocities between 4 and 17 m/s. For the opposite plate orientation it is possible for increasing gas injection to lead to smaller local skin-friction reduction at the lowest speeds. Drag reduction appears to persist for as much as 60–70 boundary-layer thicknesses downstream of the injection region. It is further shown, using a probe flush-mounted just upstream of the injection section, that there is no apparent upstream interference due to the gas injection. Spectral measurements indicate that microbubbles can cause a reduction of high-frequency shear-stress fluctuations. This suggests a destruction of some of the turbulence in the near-wall region.

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Section: Skin-friction Probe Calibration Proceduresmentioning

confidence: 99%

Measurements of local skin friction in a microbubble-modified turbulent boundary layer

1985

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“…In that case, the calibration is made in a high-turbulence environment and the high-order moments of the voltage must also be considered. Ramaprian and Tu [59] proposed an improved calibration method, with the instantaneous version of equation (21) This can be written as τ w = C 6 e 6 + C 4 e 4 + C 2 e 2 + C 0 (23) where the Cs are the new calibration constants. The highorder moments of the voltage can easily be calculated with a computer, but care must be taken that they are fully converged.…”

Section: Calibrationmentioning

confidence: 99%

Section: Calibrationmentioning

confidence: 99%

MEMS-based pressure and shear stress sensors for turbulent flows

Löfdahl

Gad‐el‐Hak

1999

Meas. Sci. Technol.

140

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From a fluid dynamics perspective, the introduction of microelectromechanical systems (MEMS) has considerably broadened the spectrum of workable experiments. A typical MEMS sensor is at least one order of magnitude smaller than traditional sensors used to measure instantaneous flow quantities such as pressure and velocity. The microsensors can resolve all relevant scales even in high-Reynolds-number turbulent flows, and arrays of microsensors make it feasible, for the first time, to achieve complete information on the effective small-scale coherent structures in turbulent wall-bounded flows. In this paper we focus on the use of MEMS for the diagnosis of turbulent shear flows and survey the status and outlook of microsensors as used for measurements of fluctuating wall pressure and wall shear stress, two quantities which we deem particularly difficult to measure with conventional probes. For both wall pressure and wall shear stress sensors, we give general background, design criteria and calibration procedure. Examples of measurements conducted with MEMS-based sensors are provided and the minute devices are compared to their larger cousins.

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“…The harsh conditions present (optically opaque, high dynamic pressure, thin boundary layers, small turbulence scales, and strong two phase character) are likely to sustain this condition for the near future. For this reason, we have relied on flush-mounted hot film probes for which the shear stress may be related to the voltage output of a constant temperature anemometer (Bellhouse and Schultz, 1966;Brown, 1967;Ramaprian and Tu, 1983). Calibration is accomplished in place using the characteristics of classical turbulent boundary layers.…”

Section: Comparison Of Air and Helium Injectionmentioning

confidence: 99%

Microbubble Drag Reduction

Merkle

Deutsch

1989

Lecture Notes in Engineering

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Over the past twenty-five years there has been extensive and sustained research aimed both at determining. techniques for reducing skin friction drag and at explaining how successful techniques work. Certainly, one reason for pursuing this research is because of our need to drive systems faster and farther for the same power, but this is only part of the motivation. An important additional rationale for the work is bound up with our continuing fascination with boundary layers --particularly turbulent boundary layers --with what makes them work the way they do and how we might intervene and change them.Research on skin friction drag reduction has two branches. The first, laminar flow control, is concerned with the delay of transition. This is usually accomplished by making the boundary layer velocity profile more stable near the wall by "filling it out". Suction, body shaping, and heating in water or cooling in air have all been employed and have shown great success in the laboratory (Hefner et al., 1977). The implementation of these successes in practical application has proven to be more difficult.The second branch of research has been concerned with reducing the skin friction drag of the turbulent boundary layer. Potential payoffs are almost as spectacular as for laminar flow control --but appear to be more realizable for actual systems. We have known for some time that the reduction of skin friction drag in a turbulent boundary layer is possible. Polymer, fibre and particle solutions are some of the best known drag reducers.' Several good reviews of these and other techniques are available (BUShnell, 1983).In the current paper we review one of the most promising areas of drag reduction research, that of microbubble injection. Although research into drag reduction by gas injection into a liquid turbulent boundary layer has been done for about twenty years, there exists no detailed review. In this first review, then, we shall describe and discuss the early results, both in the U.S. and in the Soviet Union. As most of the work done in the last ten years has been done in our laboratory at Penn State, we shall consider that work in detail. We also describe the resul ts of the few computational and theoreti ca 1 studi es that have been attempted. Finally, we summarize what we do and do not know, and how we might go about finding out more.M. Gad-el-Hak (ed.), Frontiers in Experimental Fluid Mechanics

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Calibration of a Heat Flux Gage for Skin Friction Measurement

Cited by 7 publications

References 0 publications

Measurements of local skin friction in a microbubble-modified turbulent boundary layer

Measurements of local skin friction in a microbubble-modified turbulent boundary layer

MEMS-based pressure and shear stress sensors for turbulent flows

Microbubble Drag Reduction

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