High-speed Axial Flow Compressor Research Articles

An Optimization Study of Circumferential Groove Casing Treatment in a High-Speed Axial Flow Compressor

In this paper, a numerical optimization study of single-groove casing treatment was conducted on a high-speed axial compressor. One of the aims is to find the optimal structure of a single groove that can improve compressor stability with minimal loss in efficiency. Another aim is to explore suitable parameters for rapidly evaluating the compressor stall margin. A design optimization platform has been constructed in this paper, which utilizes NSGA-II and a Radial Basis Function (RBF) neural net model to carry out the optimization. The stall margin of the compressor with A single groove was accurately determined by calculating its entire overall performance line. A Pareto front is obtained through optimization, and the optimal design can be selected from the Pareto front. By considering both stall margin and efficiency loss, one of the optimal designs was found to achieve a 7.49% improvement in stall margin with a 0.24% improvement in peak efficiency. Based on the database, the effect of design parameters of a single groove on compressor stability and performance is analyzed. A series of evaluation parameters of stall margin were compared to their degree of correlation with the real stall margin calculated by the entire overall performance line. As a result, tip blockage and momentum ratio can be used as efficient parameters for quickly evaluating the compressor stall margin without the need to calculate the entire performance curve of the compressor.

Numerical Study on End Wall Synthetic Jet to Improve Performance and Stability Margin of a High-speed Subsonic Axial Compressor Rotor

Synthetic jet has been confirmed as a novel flow control technology. However, the existing application research on synthetic jet in axial flow compressor is still confined to cascade or low-speed axial flow compressors, and rarely high-speed axial flow compressor. The effects of three vital parameters (i.e., the action position, frequency, peak velocity) on the aerodynamic performance and stability margin are systematically studied, with a high-speed compressor rotor as the object of numerical simulation. An optimal excitation position is determined, corresponding to the core position of the compressor top blockage, as indicated by the results, which increases the stability margin and efficiency of the compressor by 13.2% and 1.15% respectively. The excitation frequency has a threshold ranging from 300Hz to 600Hz. Only when the frequency of synthetic jet exceeds this threshold can it suppress the tip leakage flow. Besides, the jet peak velocity may not have a threshold. However, the higher the peak velocity, the greater the mixing loss between the jet and the mainstream of the compressor rotor will be, thus limiting the further increase of the compressor efficiency.

Approximation of hub leakage flow in a high speed axial flow compressor rotor with adjoint method

Abstract This paper focuses the effect of hub leakage flow on the performance of a high speed transonic rotor. The rotor considered here is NASA rotor 37. General computational fluid dynamics of this rotor have been unable to predict a total pressure deficit from the hub wall to the mid span height observed in the experiments. In this study, computations have been performed on the rotor with the boundary condition assumed the leakage flow from the tip gap at the upstream of the rotor. In the computations, the velocity distribution is determined on the computational domain corresponding to the location of the tip gap. The swirl velocity at the boundary is calculated with the rotational speed and the radial length of the hub wall. The radial velocity is estimated based on the leakage mass flow. However, the mass flow is an uncertain quantity, and it has effect to the prediction of the total pressure deficit. Therefore, an adjoint method has been applied for the approximation to the uncertain quantity. The simulation results using the leakage flow boundary and the result without the boundary condition have been compared with the experiment. The comparisons have shown that the boundary condition and the approximation with the adjoint method have enabled to predict the total pressure deficit.

Tip leakage flow, tip aerodynamic loading and rotating instability in a subsonic high-speed axial flow compressor rotor

Rotating instability as an unsteady flow phenomenon is closely related to rotating stall in the compressor. In this paper, dynamic pressure measurements and full-annular URANS simulations were conducted in a subsonic axial flow compressor rotor to enhance the understanding of the flow mechanism of RI. RI characterized by a frequency band in the spectrum is detected at a narrow stable operating range in the experiments. The monitoring results from simulations show that RI characterized by a frequency hump in the spectrum appears near stall condition which is consistent with the observation in the experiments. RI shifts to lower frequency band in the rotating frame with the decrease of mass flow rate. Details of the numerical flow field indicate that RI develops synchronously with the oscillation of the tip leakage flow (TLF). The tip leakage vortex (TLV) forms a low static pressure near the pressure surface side of neighboring blade through an induced vortex. It varies the tip aerodynamic loading. Both the tip aerodynamic loading and TLF get strong with the decrease of mass flow rate. The stronger TLV will form a stronger induced vortex near the pressure surface side of the neighboring blade and propel the induced vortex toward the leading edge of blade. When a high tip aerodynamic loading region is influenced by the induced vortex near the pressure surface side, the intensity of TLF in the next passage will be weakened. Then, TLF fluctuates and leads to the oscillation of neighboring blade tip aerodynamic loading as well as the oscillation of TLF issuing from the neighboring blade. The circumferential propagation of this influence process results in RI.

Stability management of high speed axial flow compressor stage through axial extensions of bend skewed casing treatment

This paper presents the experimental results to understand the performance of moderately loaded high speed single stage transonic axial flow compressor subjected to various configurations of axial extensions of bend skewed casing treatment with moderate porosity. The bend skewed casing treatment of 33% porosity was coupled with rectangular plenum chamber of depth equal to the slots depth. The five axial extensions of 20%, 40%, 60%, 80% and 100% were used for the experimental evaluations of compressor performance. The main objective was to identify the optimum extension of the casing treatment with reference to rotor leading edge which results in maximum stall margin improvements with minimum loss in the stage efficiency. At each axial extension the compressor performance is distinctive. The improvement in the stall margin was very significant at some axial extensions with 4%–5% penalty in the stage efficiency. The compressors stage shows recovery in terms of efficiency at lower axial extensions of 20% and 40% with increase in the peak stage efficiency. Measurements of flow parameters showed the typical behaviors at near stall flow conditions. Hot wire sensor was placed at the rotor upstream in the tip region to capture the oscillations in the inlet axial and tangential velocities at stall conditions. In the absence of casing treatment the compressor exhibit abrupt stall with very high oscillations in the inlet axial and tangential velocity of the flow. The extents of oscillations reduce with bend skewed casing treatment. Few measurements were also performed in the plenum chamber and salient results are presented in this paper.

Rotating Stall Observations in a High Speed Compressor—Part II: Numerical Study

In this two-part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (Part I) and numerically (Part II). The experimental observations reported in Part I are now explored through the use of 3D unsteady Reynolds-averaged Navier–Stokes (RANS) simulation. The objective is to both validate the computational model and, where possible, explore some physical aspects of the phenomena. Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part I. The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multicell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multicell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes (VSVs) are mismatched further, pushing each region deeper into stall. The numerical predictions show a credible match with the experimental findings of Part I. This suggests that a RANS modeling approach is sufficient to capture some important aspects of part span rotating stall behavior.

Rotating Stall Observations in a High Speed Compressor—Part I: Experimental Study

In this two-part paper, the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (Part I) and through the use of unsteady RANS simulations (Part II). In this paper, the behavior of an eight stage high speed compressor is studied during slow acceleration maneuvres along a fixed working line. Casing mounted pressure transducers and rotor mounted strain gages are used to examine the spectral content of any unsteadiness in the flow and its behavior across the operating range. By deliberate aerodynamic mismatching of the front stages through adjustment of three rows of variable stator vanes (VSVs), stable rotating stall is initiated. The observed behavior falls into two “families” of high and low frequency when tracked on the instrumentation. Further analysis based on the Doppler shift between the static and rotating measurements confirms that these respective phenomena are due to rotating stall of high and low cell count. Acoustic modes resulting from stall/rotor interaction are also identified. Strong correlation of the stall intensity with simple 1D meanline predicted loading parameters suggests that these families of behavior are independently linked to the stalling of different regions within the compressor.

A numerical study of the effects of injection velocity on stability improvement in high-speed compressors

The current paper presents numerical simulations for a high-speed axial-flow compressor rotor, NASA Rotor-67, with continuous air injection upstream of the rotor. A parametric study relating injection velocity to compressor stability is undertaken. The effects of injector exit velocity on blade loading and flow field are investigated and discussed. Results indicate that the injection velocity has major effects on compressor stability. The injector effectiveness is found to be maximized when the injector exit Mach number is equivalent to unity. Significant range extension in terms of reduction in stalling flow coefficient equivalent to 13.23 per cent is obtained for the case of choked injector, whereas the injection mass flow is only a small percentage of the main flowrate.

Behaviour of tip-leakage flow in an axial flow compressor rotor

The current paper reports on investigations with an aim to advance the understanding of the flowfield near the casing of a small-scale high-speed axial flow compressor rotor. Steady three-dimensional viscous flow calculations are applied to obtain flowfields at various operating conditions. To demonstrate the validity of the computation, the numerical results are first compared with available measured data. Then, the numerically obtained flowfields are analysed to identify the behaviour of tip-leakage flow, and the mechanism of blockage generation arising from flow interactions between the tip clearance flow, the blade/casing wall boundary layers, and non-uniform main flow. The current investigation indicates that the ‘breakdown’ of the tip-leakage vortex occurs inside the rotor passage at the near stall condition. The vortex ‘breakdown’ results in the low-energy fluid accumulating on the casing wall spreads out remarkably, which causes a sudden growth of the casing wall boundary layer having a large blockage effect. A low-velocity region develops along the tip clearance vortex at the near stall condition due to the vortex ‘breakdown’. As the mass flow rate is further decreased, this area builds up rapidly and moves upstream. This area prevents incoming flow from passing through the pressure side of the passage and forces the tip-leakage flow to spill into the adjacent blade passage from the pressure side at the leading edge. It is found that the tip-leakage flow exerts a little influence on the development of the blade suction surface boundary layer even at the near stall condition.

Recirculation casing treatment by using a vaned passage for a transonic axial-flow compressor

The tip leakage flow has an important influence on compressor performance particularly for the case of transonic compressors. Recirculation casing treatment is an effective approach to control the tip clearance flow which results in stability enhancement. Numerical simulations for a high-speed axial-flow compressor rotor with endwall recirculation, applying a state of the art design for the recirculation passageway are presented in the current study. Anti-swirl vanes are placed in the recirculation passageway. The effects of recirculation casing treatment on the compressor overall characteristics, stability, blade loading, and flow field are presented and discussed. Results show a significant range extension with a very small penalty in efficiency. Besides, the recirculated mass flow is only a few per cent of the main flowrate.

Stall inception in a multistage high-speed axial compressor

A comprehensive study has been conducted into the inception of stall in a multistage high-speed axial flow compressor. The compressor tested was a highly loaded, four-stage axial compressor representing the state of the art in current design technology. Data were taken at a variety of speeds, both with and without inlet distortion. High-frequency response pressure measurements were made on three of the four stages. The data were spatially Fourier analyzed for the existence of pressure waves traveling about the annulus of the compressor prior to stall. In addition, system identification methods were used to estimate the frequency and stability of such waves. In this test, these waves were found at nearly all conditions tested. However, the duration of the waves prior to stall differed markedly as a function of the speed of the compressor. The system identification results showed that the stability of these waves approached zero as the compressor was stalled. LASSICALLY, instabilities in the overall operation of a compressor have been classified as either rotating stall or surge. Both of these conditions result in a substantial decrease of the overall performance of the compressor. In this article, the inception of both rotating stall and surge will be referred to simply as stall, regardless of the final form of the instability. The theory of the formation of compressor stall has continued to evolve since the theory of Emmons et al. 1 was presented. Emmons proposed a mechanism by which a stall cell could propagate around the annulus of the compressor, typically at approximately half the rotational speed of the compressor. More recently, efforts have been made to identify the formation of these stall cells prior to the actual stall event. The linear model of Moore provides a prediction of the properties of small-amplitu de stall cells in a compressor prior to stall.2 Three properties predicted by the model are of particular interest. First, the perturbations of the uniform flowfield are composed of small amplitude sinusoidal waves that travel in the circumferential direction. Second, multiple independent modes of these waves may be found to exist simultaneously. Third, the growth and decay of these modal waves are governed by an exponential function of time. These predictions have been used as a basis to perform investigations into the early identification of compressor stall. Currently, interest exists in the experimental work being conducted in the field of prestall identification. Considerable progress has already been made in the area of low-speed axial compressors. McDougall et al. 3 established the existence of small amplitude waves traveling circumferentially around the annulus of the compressor that develop into stall cells in a continuous manner. In a more detailed study, Gamier et al. 4 confirmed the finding of McDougall in multiple configurations and extended the analysis to provide an experimental estimation of the stability of the compression system. In addition, Day's investigation of prestall phenomena found waves of varying time scales and amplitudes preceding compressor stall.5 Both Paduano et al. 6 and Day7 have used these results to

An engineering approach to blade designs for low to medium pressure rise rotor-only axial fans

Low to medium pressure rise axial fan equipment of the arbitrary vortex flow rotor-only type is widely used in industrial and commercial applications, with many of the installations and rotor designs being far from optimum. Complex computational methods exist for analyzing flows in, for example, high-speed axial flow compressors with multistage blade rows; however, the designers and manufacturers of low-speed, general-purpose axial flow fan equipment have been reluctant to embrace this technology. A simpler yet reliable design technique is presented that allows this category of ducted axial fan rotors, in the presence of swirl-free inlet flow, to be designed to achieve a specified duty with sufficient accuracy for engineering purposes. Practical blade design recommendations and limits, similar to those that exist for free vortex flow axial rotors, have been established for the arbitrary vortex flow rotor-only case. The technique employs a straightforward engineering approach to arbitrary vortex flow axial fan rotor design, and the equation set can be solved by using relatively simple numerical methods. Estimates of pressure rise and shaft power characteristics for a proposed fan/rotor design can be computed and the design loop iterated until an acceptable set of blade parameters is identified. It is also possible to analyze the performance of an existing axial fan installation as a prelude to the design of a more efficient and effective replacement rotor. Experimental data used in validating the design and analysis techniques are also presented. These data include comprehensive Cobra pressure probe surveys of local flow parameters downstream of three different low boss ratio, low solidity, arbitrary vortex flow rotors (all with circular arc camber line type blades) as well as fan performance characteristics for one of the experimental rotors configured as a direct-exhaust fan unit. Installation-dependent factors such as direct-exhaust losses and tip clearance effects are also examined. The analytical technique is shown to provide acceptable estimates of fan/rotor pressure rise performance and shaft power characteristics over a moderately wide range of blade angles and operating conditions.

The Numerical Simulation of a High-Speed Axial Flow Compressor

The advancement of high-speed axial flow multistage compressors is impeded by a lack of detailed flow field information. Recent developments in compressor flow modeling and numerical simulation have the potential to provide needed information in a timely manner. This paper, which consists of two parts, will explore this topic. The first part will address the development of a computer program to solve the viscous form of the average-passage equation system for multistage turbomachinery. Programming issues such as in-core versus out-of-core data storage and CPU utilization (parallelization, vectorization, and chaining) will be addressed. Code performance will be evaluated through the simulation of the first four stages of a five-stage, high-speed, axial flow compressor on a CRAY Y-MP8/8128 computer. The second part will address the flow physics, which can be obtained from the numerical simulation. In particular, an examination of the end-wall flow structure will be made, and its impact on blockage distribution assessed.

高速軸流圧縮機の研究 : 単段試験機による実験

高速軸流圧縮機の研究 : 単段試験機による実験