Secondary Flow due to the Tip Clearance at the Exit of Centrifugal Impellers
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The velocity distribution was measured at the exit of two different types of unshrouded centrifugal impellers under four different tip clearance conditions each; one with twenty radial blades and inducers and the other with sixteen backward-leaning blades. And the effect of tip clearance on input power was also measured. By increasing the tip clearance, the input power was hardly changed in the radial blade impeller and was reduced in the backward-leaning blade impeller. The velocity distribution normalized by the passage width between hub and shroud wall was hardly changed at the exit of the radial blade impeller by varying the tip clearance, on the other hand, the relative flow angle was reduced significantly and monotonously by an increase of tip clearance in the backward-leaning blade impeller. The change in input power due to the tip clearance was clearly related to the change of flow pattern at the exit of impeller due to the secondary flow, which is most likely caused by the component, normal to the blade, of the shear force to support the fluid in the clearance space against the pressure gradient in the meridional plane without blades.Keywords:
Shroud
Tip clearance
Slip factor
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In the centrifugal pump impeller, the fluid flows often on the curved surface slightly differing from the plane perpendicular to the impeller axis. In this report, the author has treated such cases by applying the method of series expansion, the method of generalised displacement flow, and the method of complex velocity functions.
Slip factor
Rotodynamic pump
Centrifugal force
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An investigation concerning the optimum blade loading of centrifugal impellers was performed. The three impellers with straight radial blades employed in the present study were of the same configurations except the shroud profiles which rendered to bring different diffusion ratios from each other. The static pressure distributions on blade surfaces, flow patterns within the impeller channel as well as at impeller inlet and at outlet were measured for these impellers. The effect of a secondary flow within impeller channel was clarified to some extent from the measurements. Theoretical investigation was also performed in order to compare with the experimental data.
Shroud
Slip factor
Centrifugal compressor
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In the range of very low specific speed (n_s≦100 [m, m^3/min, rpm]), performance of a centrifugal pump is much different from that of a normal n_s centrifugal pump and efficiency of the pump drops rapidly with a decrease of n_s. The purpose of this study is to make clear the internal flow characteristics and to obtain a basic knowledge of the pump performance. In order to examine the reason of unstable performance characteristics of a very low n_s centrifugal pump, the internal flow of a semi-open impeller is measured by PIV. The results show that large passage vortex and strong reverse flow at the outlet of impeller are formed at partial flow rate, and these vortex and reverse flow reduce a tangential velocity at the outlet of impeller and cause the performance instability. Slip factor of the semi-open impeller is higher than factor given by Wiesner.
Slip factor
Specific speed
Internal flow
Rotodynamic pump
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Two centrifugal compressor impellers with different meridional shape and blade angle were designed using computer-aided integrated design systems. The flow fields of the impellers were calculated by solving three-dimensional Navier-Stokes equations. Calculation results illustrate that decreasing the blade hub-to-shroud loading level can increase the impeller adiabatic efficiency, and that aft-loaded impeller can obtain higher impeller adiabatic efficiency. Changing meridional shape and blade angle can have large effects on the blade loading distribution.
Shroud
Centrifugal compressor
Slip factor
Solidity
Axial Compressor
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The pressure loss based on the tip clearance of impeller blades consists of the pressure loss induced by the leakage flow through the clearance and the pressure loss for supporting fluid against the pressure gradient in the channels and in the thin annular clearance space between the shroud and the impeller. Equations to evaluate these losses are derived and the predicted efficiency drop is compared with experimental data for two types of centrifugal impellers. Furthermore, the equations are simplified for axial impellers as a special case, and the predicted efficiency drop is compared with the experimental data for seven cases in the literature. Fair agreement demonstrates plausibility of the present model.
Shroud
Tip clearance
Slip factor
Total pressure
Centrifugal compressor
Leakage (economics)
Axial Compressor
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Citations (32)
The velocity distributions measured at the exit of two different types of unshrouded centrifugal impellers respectively under four different tip clearance conditions were reexamined with respect to the shroud wall surface. By increasing the tip clearance, the hub-to-shroud velocity distribution was hardly changed at the exit of the radial blade impeller, by contrast, the relative flow angle was reduced significantly and monotonously in the backward-leaning blade impeller. The change in input power due to the tip clearance was clearly related to the change of flow pattern at the exit of the impeller due to the secondary flow, which must be induced by the component, normal to the blade, of the shear force to support the fluid in the clearance space against the pressure gradient in the meriodional plane without blades.
Shroud
Tip clearance
Slip factor
Secondary flow
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Citations (1)
In order to provide the theories for us to design and Investigate parameters of the pump's three dimension flow field inside impeller centrifugal pump, This text establishes the turbulent flow model according to an internal turbulent flow flowing general equations inside pump and design parameters of the IB50-32-250 centrifugal pump's impeller, It analyses the distribution of speed and pressure of flow field inside impeller of Centrifugal Pump and proceeded a number imitation based on ANSYS8.0, It concluded out some main characteristics and distribute regulations of flow field inside impeller centrifugal pump, It has very important consults value for studying the internal fluxion circumstance of fluid machine's impeller.
Rotodynamic pump
Slip factor
Specific speed
Internal flow
Axial-flow pump
Volute
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Abstract Generally, there are two types of impeller design used in the axial flow blood pumps. For the first type, which can be found in most of the axial flow blood pumps, the magnet is embedded inside the impeller hub or blades. For the second type, the magnet is embedded inside the cylindrical impeller shroud, and this design has not only increased the rotating stability of the impeller but has also avoided the flow interaction between the impeller blade tip and the pump casing. Although the axial flow blood pumps with either impeller design have been studied individually, the comparisons between these two designs have not been conducted in the literature. Therefore, in this study, two axial flow blood pumps with and without impeller shrouds were numerically simulated with computational fluid dynamics and compared with each other in terms of hydraulic and hematologic performances. For the ease of comparison, these two models have the same inner components, which include a three‐blade straightener, a two‐blade impeller, and a three‐blade diffuser. The simulation results showed that the model with impeller shroud had a lower static pressure head with a lower hydraulic efficiency than its counterpart. It was also found that the blood had a high possibility to deposit on the impeller shroud inner surface, which greatly enhanced the possibility of thrombus formation. The blood damage indices in both models were around 1%, which was much lower than the 13.1% of the axial flow blood pump of Yano et al. with the corresponding experimental hemolysis of 0.033 g/100 L.
Shroud
Slip factor
Diffuser (optics)
Axial Compressor
Pressure head
Specific speed
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Single-blade centrifugal pump is used as a sewage pump widely. However, hydraulic losses increase because the impeller width is large as for single-blade centrifugal pump. It is extremely complicated, besides, because the internal flow of single-blade centrifugal pump changes greatly by an impeller position and changes by the flow rate. Therefore, a quantitative prediction and the elucidation of the generation mechanism of unsteady hydraulic losses are expected to make this kind of pump high efficiency. In this study, loss analysis was performed about two kinds of single-blade centrifugal impeller with different impeller outlet angle. As a result, the effect of the impeller outlet angle which gave it to performance and hydraulic losses was clarified. Furthermore, the momentary behavior of performance and hydraulic losses was shown, and their relations with the impeller inlet and outlet flow became clear.
Rotodynamic pump
Slip factor
Specific speed
Internal flow
Axial-flow pump
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