Measurements of Aerodynamic Wall Shear Stress With Heated Thin Film Gauges

Previous publications have demonstrated the method of heated thin film gauge aerodynamic wall shear stress calibration in a laminar flow with a favourable free stream pressure gradient. Further evidence, derived from calibrating a gauge in laminar pipe flow and flow over a wedge, supports both the format of the calibrating equation and the value of the calibration constants. The pipe flow calibration is extended into turbulent flow and it is shown that the format of the calibrating equatinn remains unchanged whilst the value of the first constant changes markedly. The calibration constants are applicable to any such gauges mounted on an aluminium substrate in air flow operated at the same overheat temperature. The calibration constants are then applied to allow measurement of the wall shear stress in a low pressure gradient region of the suction surface of a linear cascade turbine blade. Finally, these measurements are compared favourably with those taken from a calibrated Preston tube mounted on the same blade.

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Local Measurement of Loss Using Heated Thin-Film Sensors

Journal of Turbomachinery ◽

10.1115/1.2836735 ◽

1999 ◽

Vol 121 (4) ◽

pp. 814-818 ◽

Cited By ~ 7

Author(s):

M. R. D. Davies ◽

F. K. O’Donnell

Keyword(s):

Thin Film ◽

Shear Stress ◽

Wall Shear Stress ◽

Entropy Generation ◽

Free Stream ◽

Unit Area ◽

Generation Rate ◽

Entropy Generation Rate ◽

Thin Film Sensors ◽

Wall Shear

A calibration equation is derived linking the nondimensional entropy generation rate per unit area with the nondimensional aerodynamic wall shear stress and free-stream pressure gradient. It is proposed that the latter quantities, which can be measured from surface sensors, be used to measure the profile entropy generation rate. It is shown that the equation is accurate for a wide range of well-defined laminar profiles. To measure the dimensional entropy generation rate per unit area requires measurement of the thickness of the boundary layer. A general profile equation is given and used to show the range of accuracy of a further simplification to the calibration. For flows with low free-stream pressure gradients, the entropy generation rate is very simply related to the wall shear stress, if both are expressed without units. An array of heated thin film sensors is calibrated for the measurement of wall shear stress, thus demonstrating the feasibility of using them to measure profile entropy generation rate.

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Turbine Blade Aerodynamic Wall Shear Stress Measurements and Predictions

Volume 1: Turbomachinery ◽

10.1115/98-gt-562 ◽

1998 ◽

Cited By ~ 2

Author(s):

J. E. Fitzgerald ◽

A. J. Niven ◽

M. R. D. Davies

Keyword(s):

Thin Film ◽

Boundary Layer ◽

Shear Stress ◽

Wall Shear Stress ◽

Turbine Blade ◽

Incompressible Flows ◽

Pressure Gradients ◽

Suction Surface ◽

Stress Measurements ◽

Wall Shear

The correct prediction of the aerodynamic wall shear stress is a good test of a numerical codes ability to predict profile loss. Its measurement with heated thin film gauges is significantly easier than attempting a complete measurement of a turbine blade boundary layer. A modified form of previously published heated thin film gauge calibrations allow wall shear stress measurement in laminar incompressible flow with favourable pressure gradients and turbulent incompressible flows with small pressure gradients. In this paper, measurements are presented of the distribution of aerodynamic wall shear stress over the suction surface of a turbine blade in a linear cascade. Gauge voltage signal analyses show a laminar separation bubble between about 53% and 63% of suction surface length that is confirmed by surface flow visualisation. By-pass transition is detected by downstream gauges. Wall shear stress measurements are presented at two cascade incidence angles and for tripped and natural transition. The commercial code FLUENT is used to predict the surface pressure distribution, the aerodynamic wall shear stress distribution in the laminar region and the turbulent surface shear distribution for the tripped boundary layer. Comparisons are made between measurements and predictions.

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Local Measurement of Loss Using Heated Thin Film Sensors

Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education ◽

10.1115/98-gt-380 ◽

1998 ◽

Cited By ~ 1

Author(s):

Mark R. D. Davies ◽

Francis K. O’Donnell

Keyword(s):

Thin Film ◽

Shear Stress ◽

Wall Shear Stress ◽

Entropy Generation ◽

Free Stream ◽

Unit Area ◽

Generation Rate ◽

Entropy Generation Rate ◽

Thin Film Sensors ◽

Wall Shear

A calibration equation is derived linking the non-dimensional entropy generation rate per unit area with the non-dimensional aerodynamic wall shear stress and free stream pressure gradient. It is proposed that the latter quantities, which can be measured from surface gauges, be used to measure the profile entropy generation rate. It is shown that the equation is accurate for a wide range of well-defined laminar profiles. To measure the dimensional entropy generation rate per unit area requires measurement of the thickness of the boundary layer. A general profile equation is given and used to show the range of accuracy of a further simplification to the calibration. For flows with low free stream pressure gradients, the entropy generation rate is very simply related to the wall shear stress, if both are expressed without units. An array of heated thin film sensors is calibrated for the measurement of wall shear stress, thus demonstrating the feasibility of using them to measure profile entropy generation rate.

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The Calibration of a Surface Mounted Aerodynamic Wall Shear Stress Gauge in Laminar Flow With a Free-Stream Pressure Gradient

Volume 1: Turbomachinery ◽

10.1115/95-gt-127 ◽

1995 ◽

Cited By ~ 1

Author(s):

James T. Duffy ◽

Mark R. D. Davies ◽

Leona Hamilton

Keyword(s):

Shear Stress ◽

Laminar Flow ◽

Wall Shear Stress ◽

Pressure Gradient ◽

Cross Flow ◽

Calibration Method ◽

Cylindrical Shape ◽

Suction Surface ◽

Wall Shear ◽

Semi Empirical

A method of calibrating surface mounted thin film gauges to measure aerodynamic wall shear stress in laminar flow is presented. Hot wire measurements from the boundary-layer on a flat plate are used to find the first calibration constant and the shear stress predictions for a cylinder in cross flow are used to find the second. The cylindrical shape incorporates a favourable pressure gradient into the calibration method. Good agreement has been found between aerodynamic experimental results for the two shapes which suggests that a unique calibration exists. All experiments used Dantec 55R47 gauges operated at an overheat of 383 K above a reference temperature of 293 K. A new semi-empirical theory is used for the purpose of calibration. Input of experimental data enables the calculation of the equation parameters so that the new theory may be applied to a gauge mounted on a variety of surface profiles. Finally, calibrated gauges are used to measure the wall shear stress in laminar flow at four chordwise positions on the suction surface of a turbine blade in a two dimensional cascade.

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Preston-Static Tubes for the Measurement of Wall Shear Stress

Journal of Fluids Engineering ◽

10.1115/1.2910326 ◽

1994 ◽

Vol 116 (3) ◽

pp. 645-649 ◽

Cited By ~ 5

Author(s):

Josef Daniel Ackerman ◽

Louis Wong ◽

C. Ross Ethier ◽

D. Grant Allen ◽

Jan K. Spelt

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Convenient Method ◽

Pipe Flow ◽

Total Pressure ◽

Static Pressure ◽

Shear Stresses ◽

Streamline Curvature ◽

Syringe Needle ◽

Wall Shear

We present a Preston tube device that combines both total and static pressure readings for the measurement of wall shear stress. As such, the device facilitates the measurement of wall shear stress under conditions where there is streamline curvature and/or over surfaces on which it is difficult to either manufacture an array of static-pressure taps or to position a single tap. Our “Preston-static” device is easily and conveniently constructed from commercially available regular and side-bored syringe needles. The pressure difference between the total pressure measured in the regular syringe needle and the static pressure measured in the side-bored one is used to determine the wall shear stress. Wall shear stresses measured in pipe flow were consistent with independently determined values and values obtained using a conventional Preston tube. These results indicate that Preston-static tubes provide a reliable and convenient method of measuring wall shear stress.

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A Superposition Analysis of the Turbulent Boundary Layer in an Adverse Pressure Gradient

Journal of Applied Mechanics ◽

10.1115/1.4010226 ◽

1951 ◽

Vol 18 (1) ◽

pp. 95-100

Author(s):

Donald Ross ◽

J. M. Robertson

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Wall Shear Stress ◽

Turbulent Boundary Layer ◽

Velocity Profile ◽

Pressure Gradient ◽

Adverse Pressure Gradient ◽

Pressure Recovery ◽

Stress Coefficient ◽

Wall Shear

Abstract As an interim solution to the problem of the turbulent boundary layer in an adverse pressure gradient, a super-position method of analysis has been developed. In this method, the velocity profile is considered to be the result of two effects: the wall shear stress and the pressure recovery. These are superimposed, yielding an expression for the velocity profiles which approximate measured distributions. The theory also leads to a more reasonable expression for the wall shear-stress coefficient.

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