Small Perturbation Analysis of Nonuniform Rotating Disturbances in a Vaneless Diffuser

1978 ◽  
Vol 100 (4) ◽  
pp. 711-721 ◽  
Author(s):  
M. Inoue ◽  
N. A. Cumpsty
Keyword(s):  
Small Perturbation ◽  
Tangential Velocity ◽  
Present Theory ◽  
Main Flow ◽  
Wave Number ◽  
Centrifugal Impeller ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Circumferential Nonuniformity ◽  
Relative Flow

The behavior of the distorted flow discharged from a centrifugal impeller within a vaneless diffuser is examined theoretically by assuming small disturbances to a main flow. The inlet static pressure distribution is found in the calculation and allowance is made for circumferential nonuniformity in the relative flow angle. The flow is treated as incompressible and inviscid. The analysis shows that the decay of irrotational disturbances is more rapid with increasing disturbance wave number (e.g. more impeller blades) and the effect of the main flow condition on this behavior is very small. With rotational disturbances, however, the decay is slower than in the irrotational case and the effect of wave number is less. However, the phase angle between radial and tangential velocity fluctuations is found to have a strong influence on the decay processes for rotational disturbances. The present small perturbation theory is compared with the well-known Dean and Senoo theory which assumes that the relative flow angle is circum ferentially uniform. The comparison shows that the present theory predicts results very similar to the Dean and Senoo theory for impellers with large blade numbers (>20). For small numbers of blades the large circumferential nonuniformity in relative flow angle, appears at smaller radii and the inaccuracy of the Dean and Senoo theory becomes pronounced.

The Features of Flow in a Parallel-Walled Radial Vaneless Diffuser

2000 ◽  
Author(s):  
K. B. Abidogun ◽  
S. A. Ahmed
Keyword(s):  
Tangential Velocity ◽  
Maximum Flow ◽  
Calculation Model ◽  
Angle Distribution ◽  
Limited Data ◽  
Vaneless Diffuser ◽  
Centrifugal Blower ◽  
Flow Angle ◽  
Flow Features ◽  
Measurement Path

Abstract Detailed experimental investigation of flow features in a parallel-walled radial vaneless diffuser of a centrifugal blower was carried out. Maximum flow rate through the blower, at a constant impeller speed of 1500 rpm, was maintained throughout the experiment to ensure that no self-exited flow oscillation occurs in the diffuser. The symmetrical flowfield in the diffuser was measured along a radial path using an X-wire probe. The radial and tangential velocity distributions and their statistics, as well as flow angle distribution, are reported. The results presented in this paper agree well with earlier work on this subject. For instance, the flow angle at half the diffuser width, which is the position at which critical flow angle (measured from the radial direction) have been generally reported to be about 78°, did not exceed 65° from the diffuser inlet to its outlet along the measurement path. The result also showed that the flow exiting the impeller is skewed as revealed by the triple velocity product correlations. This data is a useful tool for vaneless diffuser calculation model developers as there are very limited data that paralleled the current one as expounded in the text of this paper.

Oxy-Fuel Turbine Through-Flow Design

2014 ◽  
Author(s):  
Majed Sammak ◽  
Srikanth Deshpande ◽  
Magnus Genrup
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
Tangential Velocity ◽  
Flow Angle ◽  
Power Turbine ◽  
Through Flow ◽  
The Mean ◽  
Line Design ◽  
Reaction Degree ◽  
Relative Flow

The objective of the paper is to present the through-flow design of a twin-shaft oxy-fuel turbine. The through-flow design is the subsequent step after the turbine mean-line design. The through-flow phase analyses the flow in both axial and radial directions, where the flow is computed from hub to tip and along streamlines. The parameterization of the through-flow is based on the mean-line results, so principal features such as blade angles at the mean-line into the through-flow phase should be retained. Parameters such as total inlet pressure and temperature, mass flow, rotation speed and turbine geometries are required for the through-flow modelling. The through-flow study was performed using commercial software — AxCent(™) from Concepts NREC. The rotation speed of the twin-shaft power turbine was set to 7200 rpm, while the power turbine was set to 4800 rpm. The mean-line design determined that the twin-shaft turbine should be designed with two compressor turbine stages and three power turbine stages. The through-flow objective was to study the variations in the thermodynamic parameters along the blade. The power turbine last-stage design was studied because of the importance of determining exit Mach number distribution of the rotor tip. The last stage was designed with damped forced condition. The term ‘damped’ is used because the opening from the tip to the hub is limited to a certain value rather than maintaining the full concept of forced vortex. The study showed the parameter distribution of relative Mach number, total pressure and temperature, relative flow angle and tangential velocity. Through-flow results at 50% span and mean-line results showed reasonable agreement between static pressure, total pressure, reaction degree and total efficiency. Other parameters such as total temperature and relative Mach number showed some difference which can be attributed to working fluid in AxCent being pure CO2. The relative tip Mach number at rotor exit was 1.03, which is lower than the maximum typically allowed value of 1.2. The total pressure distribution was smooth from hub to tip which minimizes the spanwise gradient of total pressure and thus reduces the strength of secondary vortices. The reaction degree distribution was presented in the paper and no problems were revealed in the reaction degree at the hub. Rotor blades were designed to produce a smooth exit relative flow angle distribution. The relative flow angle varied by approximately 5° from hub to tip. The tangential velocity distribution was proportional to blade radius, which coincided with forced vortex design. Through-flow design showed that the mean-line design of a twin-shaft oxy-fuel turbine was suitable.

Passive Control of Rotating Stall in a Parallel-Wall Vaneless Diffuser by Radial Grooves

1999 ◽  
Vol 122 (1) ◽  
pp. 90-96 ◽  
Author(s):  
Junichi Kurokawa ◽  
Sankar L. Saha ◽  
Jun Matsui ◽  
Takaya Kitahora
Keyword(s):  
Passive Control ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Remarkable Effect ◽  
Entire Flow ◽  
Parallel Wall ◽  
Theoretical Considerations

In order to control and suppress rotating stall in the diffuser of a centrifugal turbomachine, a passive method of utilizing radial shallow grooves is proposed and its effect is studied theoretically and experimentally. The results show that radial grooves of 3 mm depth on one wall or of only 1 mm depth on both walls can suppress rotating stall in a vaneless diffuser for the entire flow range. Theoretical considerations have revealed that this remarkable effect of radial grooves is caused by two mechanisms; one is a significant decrease in tangential velocity at the diffuser inlet due to mixing between the main flow and the groove flow, and the other is a remarkable increase in radial velocity due to the groove reverse flow. Both effects have the same contribution to increase the flow angle. [S0098-2202(00)02901-1]

Unsteady Flow Phenomena in Rotating Centrifugal Impeller Passages

1970 ◽  
Vol 92 (1) ◽  
pp. 65-71 ◽  
Author(s):  
E. Lennemann ◽  
J. H. G. Howard
Keyword(s):  
Unsteady Flow ◽  
Secondary Flow ◽  
Centrifugal Impeller ◽  
Bubble Flow ◽  
Hydrogen Bubble ◽  
Visualization Technique ◽  
Rotating Systems ◽  
Flow Phenomena ◽  
Relative Flow ◽  
Zero Flow

The phenomena of unsteady relative flow observed in a centrifugal impeller passage running at part capacity and zero flow are discussed. The mechanisms of passage stall for a shrouded and unshrouded impeller are investigated and a qualitative correlation is developed for the influence of secondary flow and inducer flow on the passage stall. The hydrogen bubble flow visualization technique is extended to higher velocities and rotating systems and provides the method for obtaining the experimental results.

Investigation on Effect of Curvilinear Element Blades on Centrifugal Impeller Performance

2017 ◽  
Author(s):  
Kiyotaka Hiradate ◽  
Hiromi Kobayashi ◽  
Takahiro Nishioka
Keyword(s):  
Centrifugal Compressor ◽  
Performance Test ◽  
Design Guidelines ◽  
Secondary Flows ◽  
Flow Coefficient ◽  
Numerical Calculations ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Compressor Impeller

This study experimentally and numerically investigates the effect of application of curvilinear element blades to fully-shrouded centrifugal compressor impeller on the performance of centrifugal compressor stage. Design suction flow coefficient of compressor stage investigated in this study is 0.125. The design guidelines for the curvilinear element blades which had been previously developed was applied to line element blades of a reference conventional impeller and a new centrifugal compressor impeller with curvilinear element blades was designed. Numerical calculations and performance tests of two centrifugal compressor stages with the conventional impeller and the new one were conducted to investigate the effectiveness of application of the curvilinear element blades and compare the inner flowfield in details. Despite 0.5% deterioration of the impeller efficiency, it was confirmed from the performance test results that the compressor stage with the new impeller achieved 1.7% higher stage efficiency at the design point than that with the conventional one. Moreover, it was confirmed that the compressor stage with the new impeller achieved almost the same off-design performance as that of the conventional stage. From results of the numerical calculations and the experiments, it is considered that this efficiency improvement of the new stage was achieved by suppression of the secondary flows in the impeller due to application of negative tangential lean. The suppression of the secondary flows in the impeller achieved uniformalized flow distribution at the impeller outlet and increased the static pressure recovery coefficient in the vaneless diffuser. As a result, it is thought that the total pressure loss was reduced downstream of the vaneless diffuser outlet in the new stage.

scholarly journals Numerical Investigation on the Influence of Hot Streak Temperature Ratio in a High-Pressure Stage of Vaneless Counter-Rotating Turbine

2007 ◽  
Vol 2007 ◽  
pp. 1-14 ◽  
Author(s):  
Zhao Qingjun ◽  
Wang Huishe ◽  
Zhao Xiaolu ◽  
Xu Jianzhong
Keyword(s):  
High Pressure ◽  
Secondary Flow ◽  
Heat Load ◽  
Rotor Blades ◽  
Inlet Temperature ◽  
Combined Effects ◽  
Temperature Ratio ◽  
Flow Angle ◽  
Hot Streak ◽  
Relative Flow

The results of recent studies have shown that combustor exit temperature distortion can cause excessive heat load of high-pressure turbine (HPT) rotor blades. The heating of HPT rotor blades can lead to thermal fatigue and degrade turbine performance. In order to explore the influence of hot streak temperature ratio on the temperature distributions of HPT airfoil surface, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed in a vaneless counter-rotating turbine (VCRT). The hot streak temperature ratios from 1.0 (without hot streak) to 2.4 were used in these numerical simulations, including 1.0, 1.2, 1.6, 2.0, and 2.4 temperature ratios. The hot streak is circular in shape with a diameter equal to 25%of the span. The center of the hot streak is located at 50%of span and 0%of pitch (the leading edge of the HPT stator vane). The predicted results show that the hot streak is relatively unaffected as it migrates through the HPT stator. The hot streak mixes with the vane wake and convects towards the pressure surface (PS) of the HPT rotor when it moves over the vane surface of the HPT stator. The heat load of the HPT rotor increases with the increase of the hot streak temperature ratio. The existence of the inlet temperature distortion induces a thin layer of cooler air in the HPT rotor, which separates the PS of the HPT rotor from the hotter fluid. The numerical results also indicating the migration characteristics of the hot streak in the HPT rotor are predominated by the combined effects of secondary flow and buoyancy. The combined effects that induce the high-temperature fluid migrate towards the hub on the HPT rotor. The effect of the secondary flow on the hotter fluid increases as the hot streak temperature ratio is increased. The influence of buoyancy is directly proportional to the hot streak temperature ratio. The predicted results show that the increase of the hot streak temperature ratio trends to increase the relative Mach number at the HPT rotor outlet, and decrease the relative flow angle from 25%to 75%span at the HPT rotor outlet. In the other region of the HPT outlet, the relative flow angle increases when the hot streak temperature ratio is increased. The predicted results also indicate that the isentropic efficiency of the VCRT decreases with the increase of the hot streak temperature ratio.

scholarly journals On the Mechanism of Dangerous Blade Vibration due to Blade Flow Interactions on Centrifugal Compressors

1989 ◽  
Author(s):  
U. Haupt ◽  
D. F. Jin ◽  
M. Rautenberg
Keyword(s):  
Pressure Field ◽  
Reverse Flow ◽  
Wave Number ◽  
Resonance Excitation ◽  
Blade Vibration ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Part Load ◽  
Operation Conditions ◽  
Flow Interactions

Severe blade flow interactions at part load operation conditions were investigated on a centrifugal compressor with a vaned diffuser leading to material stresses beyond the allowable values. By means of a number of measurement and analysis techniques it could be found, that a stationary periodic pressure field is produced on the circumference by the vibrating blade itself, which is induced at resonance conditions by the peripheral pressure non-uniformity due to the outlet tube. This peripheral pressure field of an integer wave number intensifies the blade resonance excitation from downstream leading to an additivity effect between wave amplitude and blade displacement. The significant role in this mechanism plays the reverse flow near the corner shroud/suction side in the impeller, occurring at part load operation, which is controlled by the interaction of the tip angle of the vibrating blade and the flow angle at that location. It could be demonstrated, that this dangerous blade vibration — in addition — is the source of a shift of the surge line towards higher mass flow, reducing the compressor operating range considerably in this operating zone.

Lateral Fluid Forces on Whirling Centrifugal Impeller (2nd Report: Experiment in Vaneless Diffuser)

1987 ◽  
Vol 109 (2) ◽  
pp. 100-106 ◽  
Author(s):  
H. Ohashi ◽  
H. Shoji
Keyword(s):  
Orbital Motion ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Test Results ◽  
Vaneless Diffuser ◽  
Fluid Forces ◽  
Damping Effect ◽  
Whirling Motion ◽  
Stiffness Matrices ◽  
Whirl Speed

Fluid forces acting on a rotating centrifugal impeller in whirling motion are studied experimentally. A two-dimensional impeller installed in a parallel walled vaneless diffuser was forced on a circular orbital motion at various positive and negative whirl speeds. The measurements show that the fluid forces exert a damping effect on the rotor at most operating conditions, but excite positive whirl when the impeller operates at a partial discharge and rotates at speeds more than twice the whirl speed. The test results were compared with those calculated by the theory described in the 1st Report. The characteristics of whirling fluid forces are examined from both the measurements and calculations. The measured fluid forces are expressed in terms of mass, damping, and stiffness matrices.

An Impact of Self-Recirculation Casing Treatment (SRCT) Configurations on Impeller Stall Margin and the Flow Field

2012 ◽  
Author(s):  
Yan Ma ◽  
Guang Xi ◽  
Guangkuan Wu
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Operating Conditions ◽  
Centrifugal Impeller ◽  
Flow Angle ◽  
Stall Margin ◽  
Casing Treatment ◽  
Swirl Velocity ◽  
Inlet Swirl ◽  
Unsteady Simulation

The present paper describes an investigation of stall margin enhancement and a detailed analysis of the impeller flow field due to self-recirculation casing treatment (SRCT) configuration of a high-speed small-size centrifugal impeller. The influence of different SRCT configurations on the impeller flow field at near-stall condition has been analyzed, highlighting the improvement in stall flow ability. This paper also discusses the influence of the SRCT configurations on the inlet flow angle, inlet swirl velocity and loss distribution in the impeller passage to understand the mechanism of the SRCT configurations in enhancing the stall margin of the impeller. The variation of the bleed flow rate at different operating conditions is also presented in this paper. Finally, the time-averaged unsteady simulation results at near-stall point are presented and compared with steady-state solutions.

Control of Shroud Leakage Loss by Reducing Circumferential Mixing

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Budimir Rosic ◽  
John D. Denton
Keyword(s):  
Significant Proportion ◽  
Tangential Velocity ◽  
Secondary Flows ◽  
Main Stream ◽  
Leakage Flow ◽  
Flow Angle ◽  
Blade Row ◽  
Stator Blade ◽  
The Difference ◽  
Mixing Losses

Shroud leakage flow undergoes little change in the tangential velocity as it passes over the shroud. Mixing due to the difference in tangential velocity between the main stream flow and the leakage flow creates a significant proportion of the total loss associated with shroud leakage flow. The unturned leakage flow also causes negative incidence and intensifies the secondary flows in the downstream blade row. This paper describes the experimental results of a concept to turn the rotor shroud leakage flow in the direction of the main blade passage flow in order to reduce the aerodynamic mixing losses. A three-stage air model turbine with low aspect ratio blading was used in this study. A series of different stationary turning vane geometries placed into the rotor shroud exit cavity downstream of each rotor blade row was tested. A significant improvement in flow angle and loss in the downstream stator blade rows was measured together with an increase in turbine brake efficiency of 0.4 %.

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