Unsteady Flow Phenomena in Rotating Centrifugal Impeller Passages

Lennemann, E.; Howard, J. H. G.

doi:10.1115/1.3445302

Cited by 51 publications

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“…It should be reported that the frequency (75 % rpm) is higher than that reported for rotating stall. Lennemann and Howard 13 have conducted a visual study of rotating stall in shrouded backward-curved centrifugal impellers and have reported frequencies from 50 to 66% rpm.…”

Section: System Description and Instrumentationmentioning

confidence: 98%

Frequency Response of Blower/Duct/Plenum Fluid Systems

Goldschmied

Wormley

1977

Journal of Hydronautics

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An analytical and experimental study has been made of the aerodynamic frequency response of the basic blower/duct/plenum system, which is one of the elements of the lifting air cushion system of surface-effect ships. An analysis has been developed that includes unstalled blower dynamics, distributed-duct effects, and plenum flexible-wall effects. Theoretical predictions may be made of pressure amplitude ratios at several system locations for variable-frequency sinusoidal modulation of the plenum exit area, of the duct discharge area, or of the blower's inlet guide-vanes. Experimental frequency-response data have been obtained in a 40 HP blower/duct/plenum laboratory system for three blower speeds, over a range of frequencies up to 50 Hz, using rotating butterfly valves at the plenum exit or at the duct discharge. These data have compared well with the analytical predictions up to -25 Hz and thus the theoretical method may be considered as validated for the lower frequencies.Nomenclature A d = duct area, ft 2 A e = exit area, ft 2 A p = plenum effective wall area, ft 2 Ai (A 2 ) = amplitudes of area variation defined in Eqs.(21) and (22), ft 2 c G = velocity of sound in air (fps) C -plenum capacitance, ft 5 /lb) d = fan impeller diameter, ft f d = duct resonant frequency, Hz f p = frequency of peak response Hz / = duct fluid inertance, Ib-sec 2 /ft 5 k = polytropic constant for air, 1.4 for an adiabatic process K p = effective plenum wall stiffness, Ib/ft L d = duct length, ft n = fan speed, rps N -number of blades in fan P = pressure, psf P u = atmospheric pressure, psf P d = pressure in duct, psf P f = fan outlet pressure, psf P p = plenum pressure, psf Q -volume flow, ft 3 /sec Q d = flow in duct, ft 3 /sec Q e = flow exiting from plenum, ft 3 /sec Q f = fan flow, ft 3 /sec Qo = nominal flow through system, ft 3 /sec R d = duct resistance, lb-sec/ft 5 R e = exit resistance, lb-sec/ft 5 R f = fan resistance, lb-sec/ft 5 S = La Place transform variable, I/sec / = time, sec T e = duct delay time, sec u = fan impeller tip speed, fps V = plenum volume, ft 3 x = positive along duct, ft y -plenum wall position, ft Z £ . = duct surge impedance, lb-sec/ft 5 a d -duct valve modulation gain, fps a. e = exit valve modulation gain, fps A ( ) = increment of quantity () above reference value X = fan blade angle, rad co = angular frequency, rad/sec -fan flow coefficient 4/ -fan pressure coefficient p = fluid density, slug/ft 3 T = a system time constant, sec TV = fan time constant, sec T P = plenum time constant, sec ( ) o = nominal value of quantity ()

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Section: System Description and Instrumentationmentioning

confidence: 98%

Frequency Response of Blower/Duct/Plenum Fluid Systems

Goldschmied

Wormley

1977

Journal of Hydronautics

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“…With regard to centrifugal impellers, Lenneman and Howard (1970), Howard and Kittmer (1975), Harada (1985), and Hamkins and Flack (1987) carried Contributed by the International Gas Turbine Institute and presented at the 36th International Gas Turbine and Aeroengine Congress and Exposition, Orlando, Florida, June 3-6, 1991. Manuscript received at ASME Headquarters February 19, 1991.…”

Section: Introductionmentioning

confidence: 99%

“…With regard to centrifugal impellers, Lenneman and Howard (1970), Kittmer (1975), Harada (1985), and Hamkins and Flack (1987) carried…”

Section: Introductionmentioning

confidence: 99%

The Effect of Tip Leakage Flow on Part-Load Performance of a Mixed-Flow Pump Impeller

Gotō

1992

Journal of Turbomachinery

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The flow phenomena around the positive slope region of the head-flow characteristic were investigated experimentally on a mixed-flow pump impeller at various tip clearances for both shrouded and unshrouded cases, A positively sloped head-flow characteristic (abrupt decrease in pressure head) was caused by the onset of extensive flow separation in the impeller at the casing-suction surface corner. The corner separation in unshrouded cases appeared at a much lo werflow rate than the shrouded case due to the favorable effect of the tip leakage flow, which displaced the wake region away from the corner. The interaction between the tip leakage flows and secondary flows and the formation of the wake regions in shrouded and unshrouded cases were explained based on experimental observation and computations by the Dawes three-dimensional Navier-Stokes code. In the shrouded case, the flow rate at which an abrupt decrease in pressure head appeared was lowered substantially by introducing a leakage flow through a slit made between the shroud and the blade tip. Inlet recirculation was triggered by the corner separation and developed more gradually for larger tip clearances. Both the increased loss, due to the extensive flow separation, and the decreased Euler's head, due to the abrupt change in flow pattern caused by the inlet recirculation, were responsible for the generation of positively sloped head-flow characteristic in the unshrouded case when the tip clearance was small, while the increased loss was the primary factor in the shrouded case. IntroductionMixed-flow pumps often show an abrupt decrease in pressure head and positively sloped head-flow characteristic when the flow rate is reduced below a critical value. In the present paper, this condition when the slope becomes positive will be referred to as "stall onset." Since the occurrence of a positively sloped characteristic is more likely to cause instabilities in a pumping system, it is usually a contractual requirement to guarantee a substantial margin between operating and stall points or to achieve a head-flow curve with a monotonously negative slope. Despite a lot of experimental investigations (see review by Engeda and Rautenberg, 1988), the flow phenomena under part-load operating condition and the generation mechanism of positively sloped head-flow characteristic are not well understood.The performance difference between shrouded impellers (most commonly used for multistage configurations) and unshrouded impellers at various tip clearances is a matter of great interest, because they often show quite different characteristics, especially at partial flow rates. With regard to centrifugal impellers, Lenneman and Howard (1970), Kittmer (1975), Harada (1985), and Hamkins and Flack (1987) carried

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“…However the performance difference between shrouded and unshrouded impellers in centrifugal compressors has, up to now, come under little investigation. Howard et al [2][3] have measured the effect on internal flow caused by a shroud in a 9-in. diameter clear plastic impeller both with and without a shroud, using the hydrogen bubble method and a hot film probe.…”

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confidence: 98%

Performance Characteristics of Shrouded and Unshrouded Impellers of a Centrifugal Compressor

Harada

1985

Journal of Engineering for Gas Turbines and Power

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The overall performance of shrouded and unshrouded identical impellers of a centrifugal compressor were tested and compared. A closed loop test stand with Freon gas as the working fluid was employed for the experiments. The inlet and outlet velocity distributions of both impellers were measured using a three-hole cobra probe and a hot-film probe to determine the velocity distribution and unsteady flows due to wakes and inlet stall. IntroductionBoth shrouded and unshrouded impellers are widely used in centrifugal compressors. The high-pressure, single-stage impellers used for turbochargers and gas turbine compressors are unshrouded because of the high stress requirements and the problems of machining and precision casting. Senoo et al.[1] report that the performance with unshrouded impeller is affected by the clearance between the casing and the impeller, especially in the region where there is a large reduction in relative velocity in the impeller channel.Multistage compressors requiring high reliability for industrial use and gas processing are widely used with shrouded impellers. However the performance difference between shrouded and unshrouded impellers in centrifugal compressors has, up to now, come under little investigation. Howard et al. [2][3] have measured the effect on internal flow caused by a shroud in a 9-in. diameter clear plastic impeller both with and without a shroud, using the hydrogen bubble method and a hot film probe. They reported that with unshrouded impellers the secondary flow in the impeller channel varies from the pressure side of the blade to the suction side due to leakage across the clearance, and that the presence of a shroud affects stall conditions at partial capacity. However, since the rotational speed was as low as 140 rpm, their study did not discuss the overall performance difference between shrouded and unshrouded impellers.In the study covered by this paper, the overall performance of shrouded and unshrouded backward impellers was compared. The circumferential Mach number of the tested impeller was varied up to unity, and a three-hole cobra probe and hot-film probe were used to measure the velocity distribution and unsteady flow at the impeller inlet and outlet.

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Unsteady Flow Phenomena in Rotating Centrifugal Impeller Passages

Cited by 51 publications

References 0 publications

Frequency Response of Blower/Duct/Plenum Fluid Systems

Frequency Response of Blower/Duct/Plenum Fluid Systems

The Effect of Tip Leakage Flow on Part-Load Performance of a Mixed-Flow Pump Impeller

Performance Characteristics of Shrouded and Unshrouded Impellers of a Centrifugal Compressor

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