Secondary Flow Due to the Tip Clearance at the Exit of Centrifugal Impellers

1990 ◽  
Vol 112 (1) ◽  
pp. 19-24 ◽  
Author(s):  
M. Ishida ◽  
Y. Senoo ◽  
H. Ueki
Keyword(s):  
Velocity Distribution ◽  
Secondary Flow ◽  
Shear Force ◽  
Input Power ◽  
Tip Clearance ◽  
The Other ◽  
Centrifugal Impeller ◽  
Meridional Plane ◽  
Flow Angle ◽  
Different Types

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.

Secondary Flow due to the Tip Clearance at the Exit of Centrifugal Impellers

1989 ◽  
Author(s):  
Masahiro Ishida ◽  
Yasutoshi Senoo ◽  
Hironobu Ueki
Keyword(s):  
Velocity Distribution ◽  
Secondary Flow ◽  
Shear Force ◽  
Input Power ◽  
Tip Clearance ◽  
The Other ◽  
Meridional Plane ◽  
Flow Angle ◽  
Different Types ◽  
Relative Flow

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.

On the Pressure Losses Due to the Tip Clearance of Centrifugal Blowers

1981 ◽  
Vol 103 (2) ◽  
pp. 271-278 ◽  
Author(s):  
M. Ishida ◽  
Y. Senoo
Keyword(s):  
Pressure Gradient ◽  
Pressure Loss ◽  
Relative Velocity ◽  
Pressure Rise ◽  
Input Power ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Clearance Ratio ◽  
Local Pressure ◽  
Pressure Losses

The pressure distribution along the shroud is measured for three types of centrifugal impeller at seven different values of tip clearance each. The change of input power due to a change of tip clearance is related to the effective blockage at the impeller tip. Since the change of input power is little for the test cases, the variation of local pressure gradient along the shroud is mostly attributed to the change of local pressure loss. The local pressure loss is related to the local tip clearance ratio and to the local pressure gradient based on the deceleration of relative velocity in the impeller. Since the local pressure gradient is largest near the throat of the impeller, for many impellers the clearance ratio at the throat is used as the representative value. The tip clearance loss is related to the clearance ratio and the pressure rise based on the deceleration of relative velocity in the impeller. A good correlation is observed in all cases at various flow rate.

Effect of Blade Tip Configuration on Tip Clearance Loss of a Centrifugal Impeller

1990 ◽  
Vol 112 (1) ◽  
pp. 14-18 ◽  
Author(s):  
M. Ishida ◽  
H. Ueki ◽  
Y. Senoo
Keyword(s):  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Meridional Plane ◽  
Leakage Flow ◽  
Clearance Ratio ◽  
Contraction Coefficient ◽  
Blade Tip ◽  
Flow Through ◽  
Annular Clearance ◽  
Blade Tip Clearance

According to the theory presented by the authors, the tip clearance loss of an un-shrouded centrifugal impeller mainly consists of two kinds of loss; one is the drag due to the leakage flow through the blade tip clearance and the other is the pressure loss to support the fluid in the thin annular clearance space between the shroud and the blade tip against the pressure gradient in the meridional plane without blades. The former is proportional to the leakage flow or the contraction coefficient of leakage flow. The authors have conducted performance tests using an impeller with 16 backward-leaning blades in three configurations of the blade tip: round edge, sharp square edge, and edge with an end-plate. The experimental tip clearance effects can be predicted by the theory assuming reasonable contraction coefficients. They are 0.91, 0.73, and 0.53 for the respective tip configurations. The impeller efficiency is improved by about 1.5 point by reducing the contraction coefficient from 0.91 to 0.53, providing that the tip clearance ratio at the exit of impeller is 0.1. More improvement is expected for an impeller with highly loaded blades where the leakage loss shares the major part of the tip clearance loss.

scholarly journals On the Pressure Losses due to the Tip Clearance of Centrifugal Blowers

1980 ◽  
Author(s):  
M. Ishida ◽  
Y. Senoo
Keyword(s):  
Pressure Gradient ◽  
Pressure Loss ◽  
Relative Velocity ◽  
Pressure Rise ◽  
Input Power ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Clearance Ratio ◽  
Local Pressure ◽  
Pressure Losses

The pressure distribution along the shroud is measured for three types of centrifugal impeller at seven different values of tip clearance each. The change of input power due to a change of tip clearance is related to the effective blockage at the impeller tip. Since the change of input power is little for the test cases, the variation of local pressure gradient along the shroud is mostly attributed to the change of local pressure loss. The local pressure loss is related to the local tip clearance ratio and to the local pressure gradient based on the decleration of relative velocity in the impeller. Since the local pressure gradient is largest near the throat of impeller is used as the representative value. The tip clearance loss is related to the clearance ratio and the pressure rise based on the deceleration of relative velocity in the impeller. A good correlation is observed in all cases at various flow rate.

Meridional shape design and the internal flow investigation of centrifugal impeller

2016 ◽  
Vol 231 (23) ◽  
pp. 4319-4330 ◽  
Author(s):  
Yan Wang ◽  
Quanlin Dong ◽  
Yulian Zhang
Keyword(s):  
Velocity Distribution ◽  
Medial Axis ◽  
Design Method ◽  
Internal Flow ◽  
Centrifugal Impeller ◽  
Shape Design ◽  
Meridional Plane ◽  
Centrifugal Fan ◽  
Constraint Equations ◽  
Meridional Shape

This paper describes an inverse design method for calculating the shape of meridional plane of centrifugal impeller. This design method permits the shroud and hub contours to be indirectly calculated by medial axis contour and constraint equations. The design process is computationally inexpensive and can conveniently modify the shroud and hub shapes as the design’s demand. Based on this design method, new constraint equations are used for a new shape design of meridional plane that lead to a uniform velocity distribution in the inlet of impeller. Numerical simulations are employed to investigate the fluid flows of centrifugal fan. After validation of the numerical strategy, the pressure and velocity distributions in centrifugal fan are illustrated. The numerical results show that the inlet performance is improved and the velocity distribution is more uniform. Furthermore, in order to understand the flow mechanism inside the centrifugal fan, the secondary flow in the blade passage and velocity distribution at the shroud and hub have been carried out a detailed investigation and study.

scholarly journals Effect of Area Ratio on the Performance of a 5.5:1 Pressure Ratio Centrifugal Impeller

1987 ◽  
Vol 109 (1) ◽  
pp. 10-19 ◽  
Author(s):  
L. F. Schumann ◽  
D. A. Clark ◽  
J. R. Wood
Keyword(s):  
Pressure Ratio ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Computer Code ◽  
Area Ratio ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Recovery Coefficient ◽  
Flow Angle ◽  
Design Point

A centrifugal impeller which was initially designed for a pressure ratio of approximately 5.5 and a mass flow rate of 0.959 kg/s was tested with a vaneless diffuser for a range of design point impeller area ratios from 2.322 to 2.945. The impeller area ratio was changed by successively cutting back the impeller exit axial width from an initial value of 7.57 mm to a final value of 5.97 mm. In all, four separate area ratios were tested. For each area ratio a series of impeller exit axial clearances was also tested. Test results are based on impeller exit surveys of total pressure, total temperature, and flow angle at a radius 1.115 times the impeller exit radius. Results of the tests at design speed, peak efficiency, and an exit tip clearance of 8 percent of exit blade height show that the impeller equivalent pressure recovery coefficient peaked at a design point area ratio of approximately 2.748 while the impeller aerodynamic efficiency peaked at a lower value of area ratio of approximately 2.55. The variation of impeller efficiency with clearance showed expected trends with a loss of approximately 0.4 points in impeller efficiency for each percent increase in exit axial tip clearance for all impellers tested. The data also indicated that the impeller would probably separate at design area ratios greater than 2.748. An analysis was performed with a quasi-three-dimensional inviscid computer code which confirmed that a minimum velocity ratio was attained near this area ratio thus indicating separation. These data can be used to verify impeller flow models which attempt to account for very high diffusion and possible separation.

scholarly journals A Simulation of Secondary Flow in Centrifugal Impeller Channel by a Stationary Three-Dimensional Curved Duct

1992 ◽  
Author(s):  
Shimpei Mizuki ◽  
Hoshio Tsujita
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Flow Patterns ◽  
Centrifugal Impeller ◽  
Meridional Plane ◽  
Blade Surface ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Qualitative Similarity

A duct with three-dimensional curvatures was employed in order to investigate the complex secondary flow patterns similar to those within centrifugal impellers. The curvature within a pair of co-cylindrical surfaces of the duct simulates that within the meridional plane of an impeller, and the curvature within the other pair of co-cylindrical surfaces perpendicular to the above-mentioned surfaces simulates the effect of the Coriolis force within the blade-to-blade surface. The computed and the measured results showed the qualitative similarity of the secondary flow patterns to those within centrifugal impellers except the effects of pressure rise by the centrifugal force generated by the impeller rotation and the tip leakage flow.

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