The mean streamwise development of pairs of longitudinal vortices embedded in an otherwise two-dimensional turbulent boundary layer was studied. Planes of closely spaced measurements of the three components of mean velocity were obtained at several streamwise locations, and the vorticity and circulation were calculated. Skin-friction measurements were also made. It was found that the rate of vorticity spreading in a vortex was greatly increased by close proximity of other vortices. The rate of streamwise circulation decrease was significantly greater for corotating vortices than for counter rotating vortices. Boundary-layer thinning and increased skin friction occured in regions where the secondary flow induced by the pairs was directed toward the wall; the boundary layer was thickened and skin friction reduced where the secondary flow was directed away from the wall.

Experimental study of the development of longitudinal vortex pairs embedded in a turbulent boundary layer

Detailed measurements of the flow field in the tip region of an axial flow compressor rotor were carried out using a rotating five-hole probe. The axial, tangential, and radial components of relative velocity, as well as the static and stagnation pressures, were obtained at two axial locations, one at the rotor trailing edge, the other downstream of the rotor. The measurements were taken up to about 26 percent of the blade span from the blade tip. The data are interpreted to understand the complex nature of the flow in the tip region, which involves the interaction of the tip leakage flow, the annulus wall boundary layer and the blade wake. The experimental data show that the leakage jet does not roll up into a vortex. The leakage jet exiting from the tip gap is of high velocity and mixes quickly with the mainstream, producing intense shearing and flow separation. There are substantial differences in the structure of tip clearance observed in cascades and rotors.

The structure of tip clearance flow in axial flow compressors

A better understanding of unsteady flow phenomena encountered in rotor-stator interactions is a key to further improvements in turbomachinery. Besides CFD methods yielding 3D flow field predictions, time-resolving measurement techniques are necessary to determine the instantaneous flow quantities of interest. Fast-response aerodynamic probes are a promising alternative to other time-resolving measurement techniques such as hot-wire anemometry or laser anemometry. This contribution gives an overview of the fast-response probe measurement technique, with the emphasis on the total system and its components, the development methods, the operation of such systems and the data processing requirements. A thorough optimization of all system components (such as sensor selection and packaging, probe tip construction, probe aerodynamics and data analysis) is the key of successful development. After description of the technique, examples of applications are given to illustrate its potential. Some remarks will refer to recent experiences gained by the development and application of the ETH FRAPreg system.

https://iopscience.iop.org/article/10.1088/0957-0233/11/7/318/pdf

Time-resolved flow measurements with fast-response aerodynamic probes in turbomachines

This report describes the calibration of a non-nulling, conical, seven-hole pressure probe over a large range of flow onset angles. The calibration procedure is based on the use of differential pressures to determine the three components of velocity. The method allows determination of the flow angle and velocity magnitude to within an average error of 1.0° and 1.0% respectively. Greater accuracy can be achieved by using high quality pressure transducers. Also included is an examination of the factors which limit the use of the probe, a description of the measurement chain, an error analysis, and a typical experimental result. In addition, a new general analytical model of pressure probe behavior is described and the validity of the model is demonstrated by comparing it with experimentally measured calibration data for a three-hole yaw meter and a sevenhole probe.

Modelling, calibration, and error analysis of seven-hole pressure probes

A novel method for extending the calibration range of five-hole probe for highly three-dimensional flows

: In many complex flow fields such as those encountered in turbomachines, the experimental determination of the steady-state, three-dimensional characteristics of the flow field are frequently required. If space limitations or other considerations make nulling techniques impractical, five- hole probles in a non-nulling mode can be employed. However, this application requires complete three-dimensional calibration data which are not usually supplied by commercial vendors. Presented in this paper are the results of programs to calibrate and employ five-hole probes of both angle-tube and prismatic geometries. Included are descriptions of the calibration technique, typical calibration data, and an accompanying discussion of the application or interpolation procedure. Also documented are the variations in the calibration data due to Reynolds number and wall proximity effects. Typical measured data are included and, where applicable, these data are validated by comparison with data obtained using other types of velocity measuring instrumentation.

/pdf/the-calibration-and-application-of-five-hole-probes-3h4xr2xhxz.pdf

A. L. Treaster

Papers

The calibration and application of five-hole probes

The calibration and application of five-hole probes