Wall Proximity Effects in Pneumatic Measurement of Turbomachinery Flows

Conventional 3-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free stream pressure near the outer wall of a turbomachine annulus may be over indicated by upto 20% of the dynamic head. This paper reports a factorial experiment in which the effects of probe wedge angle, stem length, stem shape, flow yaw and pitch angles on this so-called ‘wall proximity effect’ are quantified at representative flow Mach numbers and turbulence intensities. For a given wedge angle, the probe stem length and Mach number are shown to be statistically the most significant of the tested variables. Wall proximity effect is also shown to be influenced by the probe pitch angle, but is largely independent of yaw angle and free stream turbulence intensity.

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Investigation of Wedge Probe Wall Proximity Effects: Part 1—Experimental Study

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2817026 ◽

1997 ◽

Vol 119 (3) ◽

pp. 598-604 ◽

Cited By ~ 3

Author(s):

P. D. Smout ◽

P. C. Ivey

Keyword(s):

Large Scale ◽

Free Stream ◽

Wedge Angle ◽

Outer Wall ◽

Proximity Effects ◽

Stem Design ◽

Local Flow ◽

Dynamic Head ◽

Yaw Angle ◽

Wall Proximity

Conventional three-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. This paper reports a series of experiments aimed at quantifying this so-called “wall proximity effect.” It is shown from a factorial experiment that probe wedge angle, stem design, and free-stream Mach number all have a significant influence. The yaw angle sensitivity of wedge probes is also found to depend on the proximity of the probe to the wall of introduction. Flow visualization studies on large-scale probe models are described, and a qualitative model of the probe local flow structures is developed. This model is used to explain the near-wall characteristics of the actual size wedge probes. In Part 2 of this paper, the experimental data are used to validate CFD calculations of the flow field around a wedge probe. A simple analytical model of the probe/flow interaction is developed from the CFD solutions.

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Investigation of Wedge Probe Wall Proximity Effects: Part 1 — Experimental Study

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

10.1115/96-gt-146 ◽

1996 ◽

Author(s):

Peter D. Smout ◽

Paul C. Ivey

Keyword(s):

Large Scale ◽

Free Stream ◽

Wedge Angle ◽

Outer Wall ◽

Proximity Effects ◽

Flow Visualisation ◽

Stem Design ◽

Local Flow ◽

Dynamic Head ◽

Wall Proximity

Conventional 3-hole wedge probes fail to measure the correct static pressure when operating in close proximity to a wall or boundary through which the probe is inserted. The free stream pressure near the outer wall of a turbomachine may be over indicated by upto 20% dynamic head. This paper reports a series of experiments aimed at quantifying this so-called ‘wall proximity effect’. It is shown from a factorial experiment that probe wedge angle, stem design and free-stream Mach number all have a significant influence. The yaw angle sensitivity of wedge probes is also found to depend on the proximity of the probe to the wall of introduction. Flow visualisation studies on large scale probe models are described, and a qualitative model of the probe local flow structures is developed. This model is used to explain the near wall characteristics of the actual size wedge probes. In Part 2 of this paper, the experimental data is used to validate CFD calculations of the flow field around a wedge probe. A simple analytical model of the probe/flow interaction is developed from the CFD solutions.

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Investigation of Wedge Probe Wall Proximity Effects: Part 2—Numerical and Analytical Modeling

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2817027 ◽

1997 ◽

Vol 119 (3) ◽

pp. 605-611 ◽

Cited By ~ 2

Author(s):

P. D. Smout ◽

P. C. Ivey

Keyword(s):

Large Scale ◽

Three Dimensional ◽

Outer Wall ◽

Aerodynamic Characteristics ◽

Proximity Effects ◽

Wake Flow ◽

Scale Model ◽

Flow Structures ◽

Flow Features ◽

Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large-scale model probes were tested to understand the mechanisms responsible for this effect, by which free-stream pressure near the outer wall of a turbomachine may be overindicated by up to 20 percent dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified that control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

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Investigation of Wedge Probe Wall Proximity Effects: Part 2 — Numerical and Analytical Modelling

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

10.1115/96-gt-147 ◽

1996 ◽

Author(s):

Peter D. Smout ◽

Paul C. Ivey

Keyword(s):

Large Scale ◽

Three Dimensional ◽

Outer Wall ◽

Aerodynamic Characteristics ◽

Proximity Effects ◽

Wake Flow ◽

Scale Model ◽

Flow Structures ◽

Flow Features ◽

Wall Proximity

An experimental study of wedge probe wall proximity effects is described in Part 1 of this paper. Actual size and large scale model probes were tested to understand the mechanisms responsible for this effect, by which free stream pressure near the outer wall of a turbomachine may be over indicated by upto 20% dynamic head. CFD calculations of the flow over two-dimensional wedge shapes and a three-dimensional wedge probe were made in support of the experiments, and are reported in this paper. Key flow structures in the probe wake were identified which control the pressures indicated by the probe in a given environment. It is shown that probe aerodynamic characteristics will change if the wake flow structures are modified, for example by traversing close to the wall, or by calibrating the probe in an open jet rather than in a closed section wind tunnel. A simple analytical model of the probe local flows was derived from the CFD results. It is shown by comparison with experiment that this model captures the dominant flow features.

Download Full-text