Experimental Investigation On The Effect Of Elbow Intake On The Performance And Inlet Flow Field Of Centrifugal Compressor

Centrifugal compressors are extensively used in vehicle turbochargers and microminiature turbojet engines.Due to the limitations of the operating environment,machine space,etc.,the inlet of centrifugal compressors usually adopts a 90° elbow configuration,which leads to intake distortion and significant performance changes.The study of the asymmetric flow characteristics at the inlet of the centrifugal compressor caused by the 90° elbow provides the foundation for a deeper understanding of the causes of the performance degradation of the centrifugal compressor and for optimizing the selection of inlet pipe configurations.There are many numerical simulation studies on the performance changes and flow field structure of compressors caused by bent pipes in existing research,but there is little research on non-contact testing of inlet distortion flow field structure.In this paper,performance indicators such as pressure ratio and efficiency of centrifugal compressors with straight pipe and 90°elbow were measured,and the meticulous flow structure of the inlet pipe of the centrifugal compressor was observed using non-contact particle dynamic analyzer and particle image velocimetry technology.The flow mechanism of the changes in performance of the centrifugal compressor caused by the intake of elbows was analyzed.First of all,the centrifugal compressor experiment and observation platform was established to obtain the pressure ratio and efficiency of the centrifugal compressor under the straight pipe and 90° elbow inlet modes,and obtain and analyze the corresponding relationship between the performance changes of the centrifugal compressor and the rotation and flow rate under different intake modes.In addition,a pressure sensor with a uniform circumferential distribution at the inlet was used to measure the static pressure at the inlet of the centrifugal compressor.The results show that when the centrifugal compressor was intake with the elbow,the static pressure on the outer side of the elbow is higher than that on the inner side.At the same reduced rotational speed,the range of static pressure at the inlet was proportional to the reduced flow rate.Secondly,a combination of PDA and PIV measurement systems was used to measure the flow at the inlet of a centrifugal compressor.Analyze the axial,radial and circumferential velocity distribution of compressor inlet according to the measurement results.The results show that: with the increase of reduced rotation and reduced flow rate,the axial intake velocity of the centrifugal compressor gradually increases.Under the same operating condition,the axial velocity in the near wall region is the lowest,and the axial velocity in the center region of the pipeline is the highest.Under the elbow intake mode,there will be significant vortex distortion in the plane flow field of the inlet section of a centrifugal compressor in the form of opposing vortices.Along the circumferential direction,the maximum values of radial velocity and circumferential velocity appear at the junction of the two mainstream vortices under various operating conditions.Finally,an index for evaluating the uniformity of flow parameters,the uniformity index,was introduced to characterize the asymmetric flow at the inlet of a centrifugal compressor.Under the elbow intake mode,the radial velocity uniformity at the inlet of the centrifugal compressor is poor at the circumferential boundary of the main stream vortex,and the circumferential velocity uniformity index first increases and then decreases with the increase of the radius.Compared with the straight pipe intake mode,under the elbow intake mode,the pressure ratio change rate and circumferential velocity uniformity index present an exponential function relationship,and the efficiency change rate and circumferential velocity uniformity index present a logarithmic function relationship.