Numerical Prediction of a Performance Change in a Compressor Shrouded Impeller with Cavity Leakage Flow
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Abstract:
Generally the Shrouded type impeller is considered to free from the loss of tip leakage flow, but is is actually not possible to complete sealing between the rotating impeller and the sealing which is stay still. As a result, there is the possibility of flow leaking between impeller exit to entrance, especially with high pressure ratio compressor machine. The Cavity leakage flow is expected to influence negative effect on a machine performance and also inner flow structure.In this study, Impeller with shroud-casing gap leakage flow is simulated by numerical method (Using CFX 12.1). The influence of leakage flow on compressor performance and efficiency will be analysed. also detail flowfield change will posted.
Keywords:
Shroud
Leakage (economics)
Overall pressure ratio
Tip clearance
Slip factor
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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Citations (6)
Report presenting a program of tests to determine the effect of an integral front shroud on the performance characteristics of a centrifugal supercharger impeller. The impellers tested included a modification of a commercial semishrouded impeller and a fully shrouded impeller, which was the same as the semishrouded one except for an integral front shroud.
Shroud
Slip factor
Centrifugal compressor
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Citations (0)
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 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.
Shroud
Tip clearance
Slip factor
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Citations (2)
In the previous report, it was pointed out that leakage flow through the comparatively large blade tip clearance of an open impeller considerably affects the flow just before the capacity at which an inlet reverse flow occurs. Then, in this paper, unsteady flows at the impeller entrance were measured for a small blade tip clearance impeller and a closed impeller. For the former, especially, static pressure distribution measurements on the casing surface outside of impeller blades and the flow visualization in the impeller were performed. The effect of blade number was also studied. As a result, the effects of the impeller blade tip clearance and the blade number on the inlet reverse flow starting point were clarified.
Tip clearance
Slip factor
Axial Compressor
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Citations (2)
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)
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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Citations (17)
Shroud
Tip clearance
Slip factor
Centrifugal compressor
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Citations (6)
The velocity distribution was measured at the exit of two different types of un-shrouded centrifugal impeller under four different tip clearance conditions each; one with 20 radial blades and inducers and the other with 16 backward-leaning blades. 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. This 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.
Shroud
Tip clearance
Slip factor
Specific speed
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Citations (11)