Endwall Blockage in Axial Compressors

1999 ◽  
Vol 121 (3) ◽  
pp. 499-509 ◽  
Author(s):  
S. A. Khalid ◽  
A. S. Khalsa ◽  
I. A. Waitz ◽  
C. S. Tan ◽  
E. M. Greitzer ◽  
...  
Keyword(s):  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Axial Compressors ◽  
Clearance Flow ◽  
Flow Features ◽  
Physical Insight ◽  
Level Loading ◽  
Stagger Angle ◽  
Insight Into

This paper presents a new methodology for quantifying compressor endwall blockage and an approach, using this quantification, for defining the links between design parameters, flow conditions, and the growth of blockage due to tip clearance flow. Numerical simulations, measurements in a low-speed compressor, and measurements in a wind tunnel designed to simulate a compressor clearance flow are used to assess the approach. The analysis thus developed allows predictions of endwall blockage associated with variations in tip clearance, blade stagger angle, inlet boundary layer thickness, loading level, loading profile, solidity, and clearance jet total pressure. The estimates provided by this simplified method capture the trends in blockage with changes in design parameters to within 10 percent. More importantly, however, the method provides physical insight into, and thus guidance for control of, the flow features and phenomena responsible for compressor endwall blockage generation.

scholarly journals Endwall Blockage in Axial Compressors

1998 ◽  
Author(s):  
S. Arif Khalid ◽  
Amrit S. Khalsa ◽  
Ian A. Waitz ◽  
Choon S. Tan ◽  
Edward M. Greitzer ◽  
...  
Keyword(s):  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Axial Compressors ◽  
Clearance Flow ◽  
Flow Features ◽  
Physical Insight ◽  
Level Loading ◽  
Stagger Angle ◽  
Insight Into

This paper presents a new methodology for quantifying compressor endwall blockage and an approach, using this quantification, for defining the links between design parameters, flow conditions, and the growth of blockage due to tip clearance flow. Numerical simulations, measurements in a low speed compressor, and measurements in a wind tunnel designed to simulate a compressor clearance flow are used to assess the approach. The analysis thus developed allows predictions of endwall blockage associated with variations in tip clearance, blade stagger angle, inlet boundary layer thickness, loading level, loading profile, solidity and clearance jet total pressure. The estimates provided by this simplified method capture the trends in blockage with changes in design parameters to within 10%. More importantly, however, the method provides physical insight into, and thus guidance for control of, the flow features and phenomena responsible for compressor endwall blockage generation.

On the Interpretation of Casing Measurements in Axial Compressors

2008 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris ◽  
Sean T. Barrows ◽  
Jen-Ping Chen
Keyword(s):  
Experimental Studies ◽  
Rotating Stall ◽  
Basic Flow ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Axial Compressors ◽  
Clearance Flow ◽  
Flow Variables ◽  
Insight Into

Experimental studies of stall inception in axial compressors typically involve the measurement of basic flow variables (often pressure or velocity) with low spatial resolution. These measurements are used to make inferences about the fluid dynamics of stall. This experimental paradigm has been used by many investigators to great effect over the last several decades. However, several limitations remain which restrict the utility of these types of measurements for developing further insight into stall inception physics. Primary among these limitations is the impracticality of making measurements within the rotating blade passages. This is especially troublesome in light of recent computational studies which indicate that the generation of short length-scale rotating disturbances is related to the rotor tip clearance flow. This study utilized the results of a recent full annulus rotating stall simulation to investigate the relationships between the casing pressure field and less observable flow quantities which are believed to be causally related to the generation of rotating disturbances. The CFD results are assumed to represent the true flow physics within the compressor. To the extent that this approximation is true, these results can be used to interpret the meaning of experimental measurements of basic flow variables. These observations not only provide new insight into the interpretation of the large catalog of experimental stall measurements found in the literature, they also give directives for future measurements and numerical simulations.

Turbine Hub and Shroud Sealing Flow Loss Mechanisms

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Metodi Blagoev Zlatinov ◽  
Choon Sooi Tan ◽  
Matthew Montgomery ◽  
Tito Islam ◽  
Melissa Harris
Keyword(s):  
Flow Characteristics ◽  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Suppression Effect ◽  
Clearance Flow ◽  
Flow Loss ◽  
Purge Flow ◽  
Secondary Air ◽  
Axial Turbines

Purge air is injected through seals in the hub and shroud of axial turbines in order to prevent hot gas ingestion into the inter-stage gaps. An investigation into the losses involved with the injection of purge air has been undertaken, with the objectives of answering where the losses are generated, how they are generated, and what are the most effective ways for reducing them. In order to address these questions, a consistent framework for interpreting entropy generation as a measure of loss is developed for turbomachinery applications with secondary air streams. A procedure for factoring out distinct effects is also presented. These tools, applied to steady computations, elucidate four mechanisms by which change in loss generation is brought about due to injection of purge air: a shear layer between purge and main streams, interaction with the passage vortex system that generates radial velocity gradients, changes in wetted loss and tip clearance flow due to an increased degree of reaction, and the potential for reducing tip clearance flow for the case of purge flow injected from the shroud. An emphasis is placed on tracing these effects to specific purge flow characteristics that drive them. The understanding gained provides a rationale for the observed sensitivity of purge flow losses to the design parameters purge air mass fraction and swirl, compared to purge slot axial inclination and gap width. Preswirling of purge flow is less effective in mitigating losses in the case of shroud-injection, since there is a tradeoff with the tip clearance flow suppression effect.

Turbine Hub and Shroud Sealing Flow Loss Mechanisms

2011 ◽  
Author(s):  
Metodi Blagoev Zlatinov ◽  
Choon Sooi Tan ◽  
Matthew Montgomery ◽  
Tito Islam ◽  
Melissa Seco-Soley
Keyword(s):  
Flow Characteristics ◽  
Tip Clearance ◽  
Design Parameters ◽  
Tip Clearance Flow ◽  
Suppression Effect ◽  
Clearance Flow ◽  
Flow Loss ◽  
Purge Flow ◽  
Secondary Air ◽  
Axial Turbines

Purge air is injected through seals in the hub and shroud of axial turbines in order to prevent hot gas ingestion into the inter-stage gaps. An investigation into the losses involved with the injection of purge air has been undertaken, with the objectives of answering where the losses are generated, how they are generated, and what are the most effective ways for reducing them. In order to address these questions, a consistent framework for interpreting entropy generation as a measure of loss is developed for turbomachinery applications with secondary air streams. A procedure for factoring out distinct effects is also presented. These tools, applied to steady computations, elucidate four routes though which change in loss generation is brought about by injection of purge air: a shear layer between purge and main streams, interaction with the passage vortex system that generates radial velocity gradients, changes in wetted loss and tip clearance flow due to an increased degree of reaction, and the potential for reducing tip clearance flow for the case of purge flow injected from the shroud. An emphasis is placed on tracing these effects to specific purge flow characteristics that drive them. The understanding gained provides a rationale for the observed sensitivity of purge flow losses to the design parameters purge air mass fraction and swirl, compared to purge slot axial inclination and gap width. Pre-swirling of purge flow is less effective in mitigating losses in the case of shroud-injection, since there is a tradeoff with the tip clearance flow suppression effect.

A Study of Large Tip Clearance Flows in an Axial Compressor Blade Row

2006 ◽  
Author(s):  
Richard Williams ◽  
David Gregory-Smith ◽  
Li He
Keyword(s):  
Research Work ◽  
Axial Compressor ◽  
Axial Direction ◽  
Low Pressure ◽  
Tip Clearance ◽  
Computational Method ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
End Wall ◽  
Stagger Angle

The tip clearance flow of industrial axial compressor rotors has a significant impact on compressor performance. Most tip clearance flow research work has been undertaken in the earlier low-pressure transonic stages of compressors. The main differences between the earlier (low-pressure) and later (high-pressure) stages include blade profile, stagger angle, Mach number, blade length and tip clearance. The tip clearance in the later stages of an industrial axial compressor is relatively large due to mechanical constraints and short blading. The stagger angle is much lower and so the tip clearance flow is at a higher angle to the (negative) axial direction. In the present work, a computational method has been employed to investigate tip clearance flow from 1% span to 10% span for blading such as that found in the later stages. A pinch tip model is used to model the blade tip in a cascade with a stationary and moving end-wall. It has been found that the tip clearance flow rolls up into a vortex much later than in the earlier stages. The migration of the tip clearance vortex across the passage is much less than for the earlier stages and also the induced vortex is much weaker. Comparisons between a cascade with fixed and moving end-walls are made, the main difference being that the tip clearance flow is stronger with a moving end-wall. The 1% tip clearance flow structure with stationary end-wall is shown to be different from all other cases investigated.

Effect of Tip Clearance on the Prediction of Non-Synchronous Vibrations in Axial Compressors

2011 ◽  
Author(s):  
Martin Drolet ◽  
Huu Duc Vo ◽  
Njuki W. Mureithi
Keyword(s):  
Operating Temperature ◽  
Axial Flow ◽  
Tip Clearance ◽  
Turbine Engine ◽  
Tip Clearance Flow ◽  
Axial Compressors ◽  
Background Theory ◽  
Proposed Model ◽  
Clearance Flow ◽  
Flow Compressor

This work investigates the effect of tip clearance size and operating temperature on the predictions of the critical rotor speed at which Non-Synchronous Vibrations (NSV) can be encountered in a turbine engine axial flow compressor. It has been proposed that the tangential tip clearance flow, observed at high blade loading near stall, can act as an impinging resonant jet on the upcoming blades and could be the underlying physics behind NSV. A model, in the form of an equation to predict the critical blade tip speed at which NSV can occur, was proposed based on the Jet-Core Feedback Theory and was experimentally verified by Thomassin et al. [8]. In the equation, a factor k that was called the “tip instability convection coefficient” was measured experimentally and found to be influenced by the tip clearance size and operating temperature. This factor has a significant impact on the accuracy of the NSV predictions obtained using the proposed model. This paper propose a numerical experiment to determine the effect of tip clearance size and temperature on k, in order to improve the critical NSV tip speed predictions using the proposed model. A review of the NSV model is presented along with the relevant background theory on the subject. Two different blade geometries are simulated to provide a generic approach to the study. The leakage flow velocity is calculated to estimate k and a correlation is proposed to model the behavior of the k parameter as a function of the tip clearance size. The latter was found to significantly improve the critical NSV speed predictions. The effect of operating temperature on k is also discussed. Finally, the variation of k with the aerodynamic loading is assessed and compared with available data in the literature to strengthen the generic nature of the results.

Investigation of a Tip Clearance Cascade in a Water Analogy Rig

1986 ◽  
Vol 108 (1) ◽  
pp. 38-46 ◽  
Author(s):  
J. A. H. Graham
Keyword(s):  
Turbine Blades ◽  
Flow Region ◽  
Tip Clearance ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Tip Clearance Flow ◽  
Pressure Profiles ◽  
Clearance Flow ◽  
Hot Film ◽  
Model Features

The tip clearance flow region of high-pressure axial turbine blades for small gas turbine engines has been investigated in a water flow cascade. The blade model features variable clearance and variable endwall speeds. The cascade is scaled for Reynolds number and sized to give velocities suitable for visualization. Pressure profiles were measured on one blade, and correlated with the visualization. Unloading is found to be a major feature of the pressure field at both tip and midspan, and is intimately connected with scraping effects and the behavior of the clearance vortex. Some initial hot-film velocity measurements are also presented.

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