Performance and laser measurement results are presented for a transonic centrifugal compressor stage, equipped with a backswept rotor designed for 586 m/s tip speed and a mean relative inlet tip Mach number of 1.30. ft
The paper describes the development and the experimental as well as theoretical investigation of a new transonic, high specific speed centrifugal compressor rotor of 6.2:1 pressure ratio. Performance measurement results, laser measurements and calculated 3D results are shown for the new rotor and are compared with the corresponding data of a same type predecessor rotor. A 2% gain in stage efficiency and a 0.2 bar increase in stage pressure ratio are found at design speed by performance measurements. With the help of optical measurements and 3D stage calculations it is shown that the flow at the exit of the new rotor is more uniform/homogeneous. The degree of uniformity increases with decreasing pressure ratio, i.e. in the compressor part load region. Deeper insight into the internal rotor and the vaned diffuser flow is obtained from the 3D stage calculations showing less flow separation in the new rotor but significant secondary flow in the small span diffuser. The investigations are indicating that a further improvement of stage performance seems to be possible by an additional optimization of the vaned diffuser.
A high-specific-speed, 6:1 total pressure ratio, centrifugal compressor rotor has been improved by using knowledge gained from previous investigations on similar types of compressors as well as advanced threedimensional design calculations. The new rotor has the same main dimensions as its predecessor and was designed for the same operating point. It was tested with conventional and optical measurement techniques. Performance and optical measurements were carried out up to tip speeds of 586 m=s. The corresponding blade path frequency was 21 kHz. The investigations were supported by three-dimensional stage calculations that delivered detailed insight into the impeller and diffuser flow development. For the high-pressure region, the investigations confirmed an improved compressor performance obtained by the combined experimental/theoretical approach. The enhanced performance can be distinctly attributed to the new impeller concept. Nomenclature c = absolute velocity, m=s D1 = vaned diffuser Eta = isentropic stage efficiency M = Mach number m = mass flow rate n = shaft speed, 1= min P = pressure, N=m 2 Pi = pressure ratio r = radius red = corrected rel = relative st = static sts = isentropic, static/total stt = isentropic, total/total t = total u = circumferential speed, m=s 1, 2 = rotor inlet/rotor exit 1t = rotor-tip leading edge 3, 4 = diffuser inlet/diffuser exit
A radial compressor stage has been investigated mainly experimentally for aerodynamic stage optimization. The rotor (πt = 3.9) consists of a profiled axial inducer and a conventionally designed radial impeller. Inducer and impeller can be locked at different circumferential positions relative to each other, thus forming a tandem wheel with adjustable geometry. Conventional and Laser-2-Focus system measurements for the tandem rotor and the stage were performed at different operating points to study the influence of the circumferential clearance geometry between inducer and impeller with respect to compressor characteristics and performance. Furthermore, three-dimensional Navier–Stokes calculations are being developed at design point condition to analyze the flow field. A small influence of the inducer adjustment on the rotor characteristics is observed. The maximum rotor efficiency of 93.5 percent varies in a range of less than 1 percent depending on the different inducer positions.
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