Two different volute geometries of a radial compressor at three different operating points have been analyzed using Computational Fluid Dynamics and detailed laboratory measurements. The performance of the volutes were compared using steady-state CFD-analysis, where the volute and the impeller with diffuser were modeled separately. In addition, a time dependent simulation of the complete compressor using the sliding mesh technique was performed for one operation point. Both volutes were manufactured and the overall performance of the compressor, the pressure distribution in the volute and the flow field in the volute inlet were measured with the respective volute geometries. The results obtained from steady, quasi-steady and time-accurate simulations are compared with experimental data.
In this study, centrifugal compressor performance was predicted using CFD. Three-dimensional time-averaged impeller and volute simulations were performed using a Navier–Stokes code. The presented performance prediction method has been divided into three phases. Firstly, the impeller was calculated with a vaneless diffuser. That gives inlet boundary conditions for the volute analysis and the pressure ratio at the diffuser exit. Next, the volute analysis was performed and a static pressure recovery coefficient obtained. Finally, that result was combined with the pressure ratio prediction from the impeller analysis, and the overall compressor performance thus obtained.
A centrifugal compressor with a vaneless diffuser was studied experimentally and numerically. The main target of the study was to analyze the volute flow. Two different volute geometries was studied. The numerical solution was done by using a steady-state RANS code at both design and off-design conditions. Both calculated and measured pressure and velocity distributions are presented.
The paper describes the results of tip clearance variation experiments in centrifugal compressors. The compressors work at different peripheral Mach number speeds either with vaneless or vaned diffusers. In the experiments, the compressors were operated in a thermally steady state after which the axial positions of the shafts were changed. The changes in the performance of the compressors were recorded and analyzed. The clearance between the impeller and its housing affects the efficiency of the centrifugal compressor. The clearance is optimized to adapt to various phenomena: thermal expansions, impeller tip deflections, shaft bending and gyroscopic motions. The compressors of this study are equipped with active magnetic bearings. They contain a control system, which constantly measures and controls the position of the shaft. This gives useful information about impeller clearance variation, and the measured results are precise within 1/100 millimeters.
This paper reports on the design procedure to produce radial compressors for high speed applications. These compressors are directly connected to a high speed electric motor. Speed control is used instead of IGV and diffuser vane control, and this sets some additional requirements e.g. for the shape of the compressor performance map. It is required that at the design pressure ratio the compressor has a wide operating range in mass flow, when optimal speed control is used. It is also required that the high efficiency range of the compressor is as wide as possible. One-dimensional computation giving the basic geometry and performance map of the compressor is done with a non-commercial program. Then a geometry generation 3D program is used to define the whole compressor wheel geometry. The wheel geometry data is used in the flow and structure analyses. The compressor flow is calculated with a three-dimensional CFD-program, which has specially been modified for centrifugal compressor flow. Particularly in the optimization process of the volute, also time-dependent computation of the complete compressor using the sliding mesh technique is used. The performance of the final compressor geometry is measured in the University test facility and the test results are used to develop the design process. Up to this date, 15 different high speed compressors have been aerodynamically designed and tested in this design loop. The typical pressure ratio of the compressors ranges from 1.6 to 2.5.
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