Inlet Recirculation Of Double Sided Centrifugal Compressor With Asymmetrical Inlet And Its Study For A Wider Operating Range

With the technical level improvemen,and the large-scale application of turbocharger,in 2008 Honeywell company first proposed to apply the double sided centrifugal compressor in the small car turbocharger.The double sided centrifugal compressor has the advantages of wide flow range,small relative volume,small moment of inertia,etc.However,due to the structural form of the turbocharger,there is a significant asymmetry between two impeller inlet.At present,there is no comprehensive understanding about the internal flow characteristics of the double sided centrifugal compressor.The methods to widen the stall boundary are also under investigation.According to above two problems,in this paper,a numerical simulation method was used to study the asymmetric inlet double sided centrifugal compressor.The main research contents and results are as follows:Firstly,the inlet recirculation characteristics of double sided centrifugal compressor with asymmetric inlet structures were studied by numerical method.Mainly focused on three issues including the differences of the inlet recirculation rate in different working conditions,the circumferential non-uniform distributions of the inlet recirculation,the recirculation velocity distributions of the rear impeller upstream slot.The results show that there are some differences between the recirculation of the front impeller and that of the rear impeller in whole working conditions.In design speed,the recirculation flow rate of the rear impeller is larger than that of the front impeller in the large flow range;but in the small flow range,the recirculation flow rate of the rear impeller is smaller than that of the front impeller.In different working conditions,the recirculation velocity distributions of the front and rear impeller are non-uniform along the circumferential direction and their non-uniform levels are quite different.The circumferential non-uniform level of the recirculation velocity varies as the working conditions change.The circumferential non-uniform level of the recirculation velocity of front impeller and its distribution are determined by the static pressure distribution of the front impeller,but that of the rear impeller is decided by the coupling effects of the rear impeller inlet flow distortion,the circumferential unsymmetrical distribution of the upstream slot and the asymmetric structure of the volute.In the design rate and small flow conditions,the recirculation velocities at different circumferential positions of the mean line of the upstream slot cross-section of the rear impeller are quite different,and the recirculation velocities distribution patterns at both sides of the mean line are different.The recirculation velocity distributions in the cross-section of the upstream slot depend on the static pressure distributions in the intake ducts.Secondly,the difference on stable operating range of a double sided centrifugal compressor consisted of two impellers with different blade backswept angle was studied.Firstly,by theoretical calculation,the pressure ratio of the impeller that has different blade backswept angle is obtained,and a method for calculating the optimum impeller combination is summarized.Secondly,selected three models which has different difference of blade backswept angle to compare and analyze.Studied the effects of different impeller combinations on the flow distribution characteristics in the double sided centrifugal compressor.The results show that through the two sides of the impeller with different blade backswept angle the distribution of flow rate on both sides of the impeller can be improved,and then the stall flow of the centrifugal compressor can be reduced.The impeller combination with 10 degree difference between two sides of the impeller can delay the change of working mode,and reduce the flow of the stall.The impeller combination with a difference of 20 degrees blade backswept angle between two sides of the impeller will make the stable working range wider,and eventually make the compressor transform to the front impeller stall state.Finally,studied the difference on stable operating range of a double sided centrifugal compressor consisted of two impellers with different number of blade.By increasing the number of blade on the impeller which inlet has the low total pressure to balance the work capability and mass flow between the two sides,so as to suppress one side of the impeller from advance stall.The research results show that,after increasing the impeller's number of blade on the low total pressure inlet,the stable operating range of the double sided centrifugal compressor at the small flow rate condition can be widened.The flow rate distribution of the two sides of the impeller has a slight deterioration at the large flow rate condition,decreaseing the efficiency of the centrifugal compressor.At the small flow rate condition,the distribution of the flow rate is obviously improved,and the efficiency of the centrifugal compressor is also improved.Specifically,for the two kinds of modification in this paper,the stall boundary is widened by about 5.6% and 22.2% respectively.