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Becausofethe small passage size and limited optical access in these previous investigations, few experimental details were available about the development of secondary flow inside high- speed impeller passages. Krain (I 988) and Sipos (1991), there- fore, used vortex models to infer the vortical nature of the sec- presented in plotted form. For all measurement planes, the ondary flow from the flow angle measurements that they ac- pitchwise distributions of axial, radial, and relative tangential quired on blade-to-blade stream surfaces. Several investigations of low-speed compressors have also provided some insight into secondary flows. Nishi, Senoo, and Yamaguchi (1968) used dye in a water-flow experiment to vi- sualize the tip clearance flow. Farge, Johnson, and Maksoud (1989) used five-hole pressure probes to obtain measurements in a 1-m-diameter shrouded impeller that rotated at 500 rpm. A clearance gap was left between the blade tip and the impeller shroud in order to generate a tip clearance flow. However, as the authors point out, there was no relative motion between the blade and the shroud, so the physics of the tip clearance flow in their investigation is not the same as it would be in an unshrouded impeller. Fagan and Fleeter (1991) used laser an- emometry to measure all three velocity components in a low- speed, shrouded, mixed-flow compressor. NASA Lewis Research Center's low-speed centrifugal compressor (LSCC) was built so that detailed experimental measurements suitable for assessing the capabilities of three- dimensional Navier-Stokes codes could be made within an unshrouded centrifugal compressor impeller. The experimental configuration consisted of a backswept impeller followed by a vaneless diffuser. The rotor was designed for axial inlet flow, so inlet guide vanes were not required. The resulting rotor-only configuration enabled us to compare the laser anemometer data with results from numerical flow analysis codes that assume a steady flow in the reference frame of the rotor. In addition, the large size and low speed of the compressor generated large vis- cous regions, which enabled us to measure near-wall details with laser anemometry. The result was an excellent experimen- tal data base with which to compare the results of three- dimensional viscous flow analysis codes. A conventional pneumatic probe surveyed the spanwise dis- tributions of total and static pressures, total temperature, and flow yaw angle at stations upstream and downstream of the rotor. These probe survey data were used to calculate overall compressor performance. Both the pneumatic probe data and performance data are included in tables herein and can be used velocity were normalized by the rotor exit tip speed, as were the wire-frame and contour plots of throughflow velocity and the vector plots of secondary velocity. Detailed descriptions of the blade and flow path geometry, as well as a complete set of the laser anemometer survey data, are available on magnetic medium upon request. A complete description of the data format is given in appendix A. Symbols used in this report are defined in appendix B. This report describes in detail the data acquired and also dis- cusses measurement uncertainty. No attempt was made herein to compare our data to computational results or to use the data to study detailed flow physics. An experimental and computa- tional investigation of the development of the characteristic throughflow momentum wake in centrifugal compressors is available in the literature (Hathaway et al. (1993) and Chriss, Hathaway, and Wood (1994)). to set boundary conditions Laser anemometer axisymmetric surfaces from a CFD grid-generation routine so as to be approximately orthogonal to the casing and hub flow paths. There were nomi- nally 20 survey planes upstream, within, and downstream of the rotor. At each survey plane the data were acquired, nomi- nally, at 15 spanwise locations in intervals of 5-percent-of-span from the shroud. At each survey point, the axial, radial, and relative tangential velocity components were measured and recorded on a magnetic medium at a resolution of 1000 points The LSCC is designed to duplicate the flow fields of a high- speed subsonic centrifugal compressor in a large low-speed machine. Thus the essential flow physics of the flow field can be investigated in detail. A schematic diagram of the LSCC facility is shown in figure 1. Air is drawn into the facility room through a filtered vent in the roof and then past a bank of steam pipes and louvers de- signed to control the air temperature to within +1 °F for mass flows up to 45 kg/sec. The facility room air is then drawn into the plenum through a bank of air straighteners contained be- tween two mesh screens. Next, the air passes through a spe- cially designed bellmouth with a 10:i area contraction. From there it flows into the compressor and exits through a specially designed throttle valve at the entrance to the collector. The throttle valve consists of two concentric overlapping rings with holes that have been drilled in each ring and that slide relative to each other to produce a throttle. This valve design was cho- sen to minimize circumferential asymmetry in the static pres- sure distribution at the exit, such as is typically found in scroll- type collectors. The bellmouth, inlet transition piece, and shroud flow path were machined together to minimize any boundary layer disturbance that might be caused by a step in the flow path. A complete description of the facility is provided by Wood, Adam, and Buggele (1983) and Hathaway, Wood, and Wasserbauer (i 992). for computational surveys were codes. conducted along of revolution that were constructed per rotor blade pitch. However, for presentation purposes and to provide more manageable data sets, the data were routinely averaged to a resolution of 200 points per rotor blade pitch. To keep the size of this report manageable, all laser data are Apparatus Low-Speed Centrifugal Compressor FacilityPDF Image | Laser anemometer measurements of the three-dimensional rotor flow
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