| Budget Amount *help |
¥5,900,000 (Direct Cost: ¥5,900,000)
Fiscal Year 1985: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1984: ¥4,900,000 (Direct Cost: ¥4,900,000)
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| Research Abstract |
Although a transonic centrifugal compressor develops a very high pressure ratio, it can hardly change the flow rate at a given shaft speed, therefore, it is seldom used for industrial applications. In this project an impeller was designed and tested clarifying the problems relative to stall and choke which decide the flow range.
First of all, a CAD system for an impeller design was developed using a quasi-three dimensional flow analysis together with empirical relations in the literature. In order to avoid a strong shock in the inducer, the curvature of blades were made weak up to the throat. At the exit the blades were made backward leaning by 40 deg to achieve stable characteristics.
In order to secure good boundary conditions in the test, a vaneless diffuser must be installed downstream while the stall limit of the compressor should not be affected by the diffuser. Therefore,a very short vaneless diffuser was adopted. In addition to the impeller characteristics, the condition of flow at the impeller exit, the pressure distribution along the shroud and the behaviour of shock waves near the inducer were examined using dynamic pressure transducers and a laser velocimeter.
The inlet Mach number and the incidence angle evaluated by a flow analysis agreed well with the measured data by the laser velocimeter at subsonic inlet conditions. However, at supersonic inlet conditions shock waves were generated and they not only modified the flow pattern but also changed the cause of inducer stall. Therefore, a new stall criterion is required for supersonic inlet conditions.
The impeller combined with short vane diffusers and with channel diffusers will be tested soon.
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