This paper addresses the use of 5-hole probes in the testing of industrial centrifugal compressors. The 5-hole probes utilized for this work are of the conical-tip type and were used in a non-nulling configuration (i.e., the probes do not need to be rotated or moved in any way during the tests). These 5-hole probes proved to be fairly robust, making them practical for a nonlaboratory setting such as an industrial multistage compressor test stand. A discussion of 5-hole probes and how they function is provided, including an overview of the mathematical formulations and calibrations required to translate the pressure data gathered from the 5 holes into static and total pressures, velocities and flow angles. A method to transform these variables from a probe-based coordinate system to a machine-based coordinate system is also presented and schematics of this process are provided to aid the reader’s understanding. The testing performed on a prototype multistage centrifugal compressor using 5-hole probes is also discussed, showing that the probes provided valuable insight into the flowfield exiting the impellers and at the return bend. The hub-to-shroud velocity profile exiting an impeller was found to be more skewed than expected and was contributing to poor performance in the downstream stationary components. The measured flowfield from one of the tests is also compared against 3-D CFD results and comments are offered regarding the agreement between the analytical and measured results. Advantages and disadvantages of 5-hole probes as compared to more conventional instrumentation are presented. Finally, conclusions are drawn regarding the value of 5-hole probe data in the development and/or troubleshooting of high performance turbomachinery and in the validation/calibration of design and analysis tools.

The paper addresses the use of a rib style (partial height) vaned diffuser to improve the flowfield downstream of a high flow coefficient centrifugal impeller. Empirical and analytical (3-D CFD) results are presented for both the original vaneless diffuser and the replacement rib configuration. Comparisons are made between the CFD results and the data obtained through single stage rig (SSTR) testing. Comments are offered regarding the qualitative and quantitative agreement between the empirical and analytical results.

This document presents an overview of impeller inlet relative Mach number, how the parameter is calculated, and its importance as an indicator of impeller performance. Comments are also offered regarding the comparison of inlet relative Mach numbers obtained from different compressor vendors. A sample impeller is used to illustrate the various methods used to calculate the inlet relative Mach number. Test data for that impeller is also offered to indicate the performance map achievable with high Mach number designs. Please note that this document is not intended to be an all-inclusive treatment of the subject; rather, it summarizes the OEM’s methodologies and perspective.

This paper addresses the use of 5-hole probes in the testing of industrial centrifugal compressors. The 5-hole probes utilized for this work are of the conical-tip type and were used in a non-nulling configuration (i.e. the probes do not need to be rotated or moved in any way during the tests). These 5-hole probes proved to be fairly robust, making them practical for a non-laboratory setting such as an industrial multistage compressor test stand. A discussion of 5-hole probes and how they function is provided, including an overview of the mathematical formulations and calibrations required to translate the pressure data gathered from the 5 holes into static and total pressures, velocities and flow angles. A method to transform these variables from a probe-based coordinate system to a machine-based coordinate system is also presented and schematics of this process are provided to aid the reader’s understanding. The testing performed on a prototype multistage centrifugal compressor using 5-hole probes is also discussed showing that the probes provided valuable insight into the flowfield exiting the impellers and at the return bend. The hub-to-shroud velocity profile exiting an impeller was found to be more skewed than expected and was contributing to poor performance in the downstream stationary components. The measured flowfield from one of the tests is also compared against 3-D CFD results and comments are offered regarding the agreement between the analytical and measured results. Advantages and disadvantages of 5-hole probes as compared to more conventional instrumentation are presented. Finally, conclusions are drawn regarding the value of 5-hole probe data in the development and/or troubleshooting of high performance turbomachinery and in the validation / calibration of design and analysis tools.

The paper discusses a computational fluid dynamics (CFD) study done to assess the influence of cover or shroud curvature on impeller performance. The paper describes the various designs and the CFD and finite element analyses (FEA) methods used. Aerodynamic and mechanical analysis results are presented for four impellers of varying cover curvature and axial length. Comments are offered regarding the mechanical issues that must be considered when increasing the length of impellers.