Aerodynamic Optimization of a Centrifugal Fan Using Response Surface Methodology

In this paper, the optimization scheme of a centrifugal fan under the constraints of the total pressure difference, efficiency and shaft power was carried out. The blade inlet angle ?1A and the blade outlet angle ?2A of the centrifugal impeller were optimized using the Response Surface Methodology (RSM). Nine optimization cases were presented. The aerodynamic performance and the flow field of the optimized model were carefully compared with the original model. The results show that the total pressure difference and the total-pressure efficiency increase by 5.7% and 4.2% respectively after the optimization. Compared with the original fan, the flow field inside the impeller of the optimized fan has been improved. The flow separation existing around the blade suction surface outlet is suppressed significantly. For fields in the volute, the optimization scheme has reduced the local vortex intensity and weakened the vortex scale. The flow field stability around the volute tongue is also correspondingly improved.

Influence of Magnetic Force on the Flow Stability in a Rectangular Duct

The stability of the flow under the magnetic force is one of the classical problems in fluid mechanics.In this paper,the flow in a rectangular duct with different Hartmann(Ha)number is simulated.The finite volume method and the SIMPLE algorithm are used to solve a system of equations and the energy gradient theory is then used to study the(associated)stability of magnetohydrodynamics(MHD).According to the energy gradient theory,K represents the ratio of energy gradient in transverse direction and the energy loss due to viscosity in streamline direction.Position with large K will lose its stability earlier than that with small K.The flow stability of MHD flow for different Hartmann(Ha)number,from Ha=1 to 40,at the fixed Reynolds number,Re=190 are investigated.The simulation is validated firstly against the simulation in literature.The results show that,with the increasing Ha number,the centerline velocity of the rectangular duct with MHD flow decreases and the absolute value of the gradient of total mechanical energy along the streamwise direction increases.The maximum of K appears near the wall in both coordinate axis of the duct.According to the energy gradient theory,this position of the maximum of K would initiate flow instability(if any)than the other positions.The higher the Hartmann number is,the smaller the K value becomes,which means that the fluid becomes more stable in the presence of higher magnetic force.As the Hartmann number increases,the K value in the parallel layer decreases more significantly than in the Hartmann layer.The most dangerous position of instability tends to migrate towards wall of the duct as the Hartmann number increases.Thus,with the energy gradient theory,the stability or instability in the rectangular duct can be controlled by modulating the magnetic force.