The unsteady flows caused by the interaction between the impeller and the volute in a high-speed micro centrifugal pump are numerically studied. The internal flows of both with and without cavitations are analyzed usi...The unsteady flows caused by the interaction between the impeller and the volute in a high-speed micro centrifugal pump are numerically studied. The internal flows of both with and without cavitations are analyzed using the CFX. The characteristics of unsteady pressure on the blade surfaces and the symmetric plane of the volute are presented and compared. The results show that the amplitudes of pressure fluctuations of critical cavitation on the blade pressure surface(PS) are bigger as compared with those at the non-cavitation condition, but on the suction surface(SS), the situation is on the contrary. When cavitation occurs, reduction of load in the impeller is a result. In the present study, such reduction of load is observed mainly on the first half of the blades. Pressure fluctuations at five monitoring points, denoted by WK1 to WK5 in the volute, are also analyzed. No matter at the critical cavitation or at the non-cavitation conditions, the monitored pressure fluctuations are at the same frequencies, which equal to the blade passing frequency(BPF) and its multiples. However, the amplitudes of the fluctuations at critical cavitation condition are considerably stronger, as compared with those for without cavitation.展开更多
In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances t...In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances to the shear layer so as to change the flow mixing. This passive strategy has not been attempted so far.A convergent nozzle with a cylindrical extension is selected as the baseline case. Three nozzles with pores on the inner wall are set up. Validations of the numerical settings are carried out, then the compressible turbulent jets at the exit Mach number M_j=0.6 in the four nozzles are calculated by large eddy simulations(LES), while the radiated sounds are predicted by the FW-H acoustic analogy. The results show that the blind holes have produced some effects on weakening the turbulence intensity in the shear layer. Comparison reveals that both temporal and spatial correlations of the turbulent fluctuations in the modified cases are suppressed to some extent. Meanwhile,the porous nozzles are shown to suppress the pairing of vortices and enhance the flow mixing, and therefore, the development of shear layer and the fragmentation of large scale vortices are accelerated.展开更多
The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems ...The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the blade.At the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated.Using the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the unsteadiness.At the operating points near the PEP,the main flow is weaker than the TLF and the interface moves upstream.The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced unsteadiness.The explanation is demonstrated by numerical results.展开更多
In this paper, laminar and turbulent flows of pseudoplastic fluids(0.1% and 0.2% by weight aqueous solutions of carboxymethylcellulose) in a square duct of strong curvature were measured using an ultrasonic Doppler ve...In this paper, laminar and turbulent flows of pseudoplastic fluids(0.1% and 0.2% by weight aqueous solutions of carboxymethylcellulose) in a square duct of strong curvature were measured using an ultrasonic Doppler velocimetry and microphones. Streamwise velocity in cross-sections of the duct and the fluctuating pressure on walls were measured for different flow rates. The velocity contours and their development along the duct were presented and compared with benchmark experiments by Taylor, Whitelaw and Yianneskis(1982) which were for the laminar and turbulent flows of water. The spectra of fluctuating wall pressures were also presented and analyzed. The objective of this paper was to provide a basis for understanding the pseudoplastic fluid flows in curved ducts. The results were also intended for use in the further development of numerical methods and turbulence models for shear-thinning fluids.展开更多
基金funded by the National Natural Science Foundation of China under Grants 51176048 and 51576067
文摘The unsteady flows caused by the interaction between the impeller and the volute in a high-speed micro centrifugal pump are numerically studied. The internal flows of both with and without cavitations are analyzed using the CFX. The characteristics of unsteady pressure on the blade surfaces and the symmetric plane of the volute are presented and compared. The results show that the amplitudes of pressure fluctuations of critical cavitation on the blade pressure surface(PS) are bigger as compared with those at the non-cavitation condition, but on the suction surface(SS), the situation is on the contrary. When cavitation occurs, reduction of load in the impeller is a result. In the present study, such reduction of load is observed mainly on the first half of the blades. Pressure fluctuations at five monitoring points, denoted by WK1 to WK5 in the volute, are also analyzed. No matter at the critical cavitation or at the non-cavitation conditions, the monitored pressure fluctuations are at the same frequencies, which equal to the blade passing frequency(BPF) and its multiples. However, the amplitudes of the fluctuations at critical cavitation condition are considerably stronger, as compared with those for without cavitation.
基金funded by the National Natural Science Foundation of China under Grant 51576067
文摘In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances to the shear layer so as to change the flow mixing. This passive strategy has not been attempted so far.A convergent nozzle with a cylindrical extension is selected as the baseline case. Three nozzles with pores on the inner wall are set up. Validations of the numerical settings are carried out, then the compressible turbulent jets at the exit Mach number M_j=0.6 in the four nozzles are calculated by large eddy simulations(LES), while the radiated sounds are predicted by the FW-H acoustic analogy. The results show that the blind holes have produced some effects on weakening the turbulence intensity in the shear layer. Comparison reveals that both temporal and spatial correlations of the turbulent fluctuations in the modified cases are suppressed to some extent. Meanwhile,the porous nozzles are shown to suppress the pairing of vortices and enhance the flow mixing, and therefore, the development of shear layer and the fragmentation of large scale vortices are accelerated.
基金funded by the National Natural Science Foundation of China under Grant 50876031by Shanghai Municipal Education Commission under Grant 10ZZ40
文摘The self-induced unsteadiness in tip leakage flow(TLF)of a micro-axial fan rotor is numerically studied by solving Reynolds-averaged Navier-Stokes equations.The micro-axial fan,which is widely used in cooling systems of electronic devices,has a tip clearance of 6%of the axial chord length of the blade.At the design rotation speed,four cases near the peak efficiency point(PEP)with self-induced unsteadiness and four steady cases which have much weaker pressure fluctuations are investigated.Using the"interface"separating the incoming main flow and the TLF defined by Duet al.[1],an explanation based on the propagation of the low energy spot and its multi-passing through the high gradient zone of the relative total pressure,is proposed to clarify the originating mechanism of the unsteadiness.At the operating points near the PEP,the main flow is weaker than the TLF and the interface moves upstream.The low energy spot which propagates along in the close behind of the interface has opportunity to circulate in the circumferential direction and passes through the sensitive interfaces several times,a slight perturbation therefore may be magnified significantly and develops into the self-induced unsteadiness.The explanation is demonstrated by numerical results.
基金funded by the National Natural Science Foundation of China under Grant No.51176048
文摘In this paper, laminar and turbulent flows of pseudoplastic fluids(0.1% and 0.2% by weight aqueous solutions of carboxymethylcellulose) in a square duct of strong curvature were measured using an ultrasonic Doppler velocimetry and microphones. Streamwise velocity in cross-sections of the duct and the fluctuating pressure on walls were measured for different flow rates. The velocity contours and their development along the duct were presented and compared with benchmark experiments by Taylor, Whitelaw and Yianneskis(1982) which were for the laminar and turbulent flows of water. The spectra of fluctuating wall pressures were also presented and analyzed. The objective of this paper was to provide a basis for understanding the pseudoplastic fluid flows in curved ducts. The results were also intended for use in the further development of numerical methods and turbulence models for shear-thinning fluids.