Investigations Of The Static Pressure Characteristics Around The Casing Wall In Centrifugal Compressor And The Stall Inception Location Of The Inlet

The centrifugal compressor has been widely used in the military and civilian areas.As the most widely used air compression system,it is also employed in turbochargers,micro turbojet/turbofan engine and turbine shaft engine.The stall of the centrifugal compressor has always been concerned,that is because the stall not only influences the operating range but also impacts on the safety and reliability of the compression system.The stall inception is the transition stage from the normal flow to the stall,the extant studies have made great progress about the stall type,the development and the and the criterion,but few researches pay attention to the key problems about the stall inception of the compressor with the asymmetric structure.The non-axisymmetric geometry structure of the volute leads to the uneven circumferential distribution of the static pressure,which adversely propagates into the inlet and directly affects the inlet flow field.The corresponding relation between the circumferential location of the stall inception and the non-axisymmetric volute is hardly studied.On the other hand,due to the space limitation of the compression system,bent pipes with different installation angles are usually used in the compressor inlet,the coupling mechanism between bent pipes and volute on the inlet stall inception is rarely published.Therefor,it is necessary to reveal the relationship between the stall inception location and the non-axisymmetric geometry structure.Moreover,the static pressure distribution and its propagation routes around the casing wall is firstly confirmed to correspond to the above two questions.In this paper,the above three aspects are studied.The static pressure characteristics around the centrifugal compressor casing wall is firstly compared through the experimental and numerical methods,and the reverse propagation routes of the pressure fluctuation induced by the volute tongue through the blade channels are also be described.In order to analyze the circumferential distribution of the static pressure under the different speeds at the full flow rate,seventy-two static pressure measuring probes including the six circumferential position and the twelve meridional position are installed around the casing wall.Through analyzing the experimental results,the circumferential static pressure has the uniform distribution at the peak efficiency point.At the small flow rate,the circumferential distribution of the static pressure not only has the peak static pressure point induced by the volute tongue but also has the bulge phenomenon,which also appears near the design flow rate.The stall inception most likely occurs at the static pressure peak or the static pressure bulge region.The circumferential static pressure distribution at the leading edge of the splitter blade is almost the same at different small flow rates.Meanwhile,the circumferential static pressure distribution has the two peaks phenomenon including the peak static pressure region and the static pressure bulge,which has the approximately 180° circumferential difference between the two peak points.On this basis,the stall pattern of this compressor is confirmed through the flow structure variation.The internal relationship between the stall inception and the volute tongue is clarified.Therefor,the formation reason of the stall inception for a centrifugal compressor with volute is illuminated.According to the circumferential characteristics of the peak static pressure around the casing wall,the blocking effect of volute tongue results in high static pressure area near the 55° region at the small flow rate,the disturbance-wave caused by high static pressure adversely propagates to the diffuser,and shapes the static pressure peak value inside the diffuser from the outlet to the inlet,which also adversely propagates to the impeller inlet about the 115° location,and induces the leading edge spillover near the corresponding impeller,thus the spike-type stall appears.Therefore,the stall inception of this centrifugal compressor is induced by the volute tongue,and the volute tongue determines the stall inception location.Based on the influence of the non-axisymmetric geometry structure of the volute on the inlet stall inception location of the compressor with straight pipe,different installation angles of bent pipes are studied for the coupling mechanism between bent pipes and volute on the inlet stall location.The first model M1(115°)illustrates that the inlet low total pressure region caused by the bent pipe and the outlet high static pressure induced by the volute tongue mutual influence the same impeller passage,and the model M2(295°)has the symmetrical installation angle.Through comparing the influence of the different installation angle of the bent pipe on the flow field and the stall process of the centrifugal compressor,for the model M1,the inlet low total pressure region caused by the bent pipe and the outlet high static pressure induced by the volute tongue mutual influence the same impeller passage,and the leading edge spillover appears at the 115° location.However,for the model M2,the inlet low total pressure region and the outlet high static pressure mutual affect the different impeller passage.The leading edge spillover firstly occurs at the 295° location because of the inlet distortion and then disappears,the second spillover appears in the 115° location under the reversed propagation of the outlet high pressure region induced by the volute tongue,and the leading edge spillover of the model M2 is relatively slow.Meanwhile,the static temperature rises sharply and the axial velocity drops significantly at the spillover region during the stall process because of the recirculating flow.These results indicate that the coupling interaction between the inlet low total pressure and the outlet high static pressure jointly determines the stall inception location at the centrifugal compressor inlet.