Showing papers on "Axial compressor published in 1999"

The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics

Abstract: The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubblelike recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow, resulting from the contraction of the bubblelike structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise, and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

Role of Blade Passage Flow Structurs in Axial Compressor Rotating Stall Inception

Abstract: The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors' knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (the movement of the tip clearance vortex forward of the leading edge) depends upon local flow phenomena related to the tip clearance with the implication that for this and possibly other stall mechanisms the flow structure within the blade passages must be addressed to explain the stability of an axial compression system that exhibits such short length-scale disturbances.

Centrifugal compressor surge and speed control

Abstract: Previous work on stabilization of compressor surge is extended to include control of the angular velocity of the compressor. A low-order centrifugal compressor model is presented, where the states are mass flow, pressure rise, and rotational speed of the spool. Energy transfer considerations are used to develop a compressor characteristic. In order to stabilize equilibria to the left of the surge line, a close coupled valve is used in series with the compressor. Controllers for the valve pressure drop and spool speed are derived. Semiglobal exponential stability is proved using a Lyapunov argument.

Endwall Blockage in Axial Compressors

Abstract: 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.

A Computational Model for Short-Wavelength Stall Inception and Development in Multistage Compressors

Abstract: This paper presents a computational model for simulating axial compressor stall inception and development via disturbances with length scales on the order of several (typically about three) blade pitches. The model was designed for multistage compressors in which stall is initiated by these “short-wavelength” disturbances, also referred to as spikes. The inception process described is fundamentally nonlinear, in contrast to the essentially linear behavior seen in so-called “modal stall inception”. The model was able to capture the following experimentally observed phenomena: (1) development of rotating stall via short-wavelength disturbances, (2) formation and evolution of localized short-wavelength stall cells in the first-stage of a mismatched compressor, (3) the switch from long to short-wavelength stall inception resulting from the re-staggering of the inlet guide vane, (4) the occurrence of rotating stall inception on the negatively sloped portion of the compressor characteristic. Parametric investigations indicated that: (1) short-wavelength disturbances were supported by the rotor blade row, (2) the disturbance strength was attenuated within the stators, and (3) the reduction of inter-blade row gaps can suppress the growth of short-wavelength disturbances. It is argued that each local component group (rotor plus neighboring stators) has its own instability point (i.e., conditions at which disturbances are sustained) for short-wavelength disturbances, with the instability point for the compressor set by the most unstable component group.

Jet assisted counter rotating wind turbine

Abstract: A jet assisted counter rotating wind turbine comprising: a pair of counter rotating rotors to amplify the relative velocity of the magnetic flux in the air gap of an alternator, a dual purpose co-axial device that serves the role of an alternator to generate electricity as well as a torque transmission means, an axial compressor to energize the low energy air mass taken from the downstream wake region, and an actively controlled piezoelectric actuator device to deform the trailing edge section to maintain optimum air load distribution at all wind speeds without causing any structural damage in gusty environment, has been conceived and is now reduced to practice. The proposed wind turbine achieves a substantially high value of energy efficiency factor, while theoretically possible factor is about 69 per cent. Hence, the turbine unit can be built using smaller and lighter rotors in contrast to those of prior art. Furthermore, these turbines can be installed in low speed wind environment wherein the prior art turbines do not produce any useful energy.

Modeling and control of compressor flow instabilities

Abstract: Compressors are widely used for the pressurization of fluids. Applications involve air compression for use in aircraft engines and pressurization and transportation of gas in the process and chemical industries. The article focuses on two commonly used types of continuous flow compressors: the axial compressor, where the gaseous fluid is processed in a direction parallel to the rotational axis, and the radial or centrifugal compressor, where the pressurized fluid leaves the compressor in a direction perpendicular to the rotational axis. In these machines, the entering fluid is pressurized by first accelerating it via the kinetic energy imparted in the rotors and then converting the kinetic energy into potential energy by decelerating the fluid in diverging channels. Toward low mass flows, stable operation of axial and radial compressors is constrained by two aerodynamic flow instabilities: rotating stall and surge. The article gives an overview of the current state of modeling and control of these instabilities.

Propagation of Multiple Short-Length-Scale Stall Cells in an Axial Compressor Rotor

Abstract: Evolution and structure of multiple stall cells with short-length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, a short-length-scale stall cell appeared at first, but did not grow rapidly in size, unlike a so-called spike-type stall inception observed in many multistage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, the size of which was on the same order of the inception cell (a few blade spacings), were rotating at 72 percent of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long-length-scale wave appeared overlapping the multiple short-length-scale waves, then developed to a deep stall state with a large cell. In order to capture the short-length-scale cells in the mild stall state, a so-called double phase-locked averaging technique has been developed, by which the flow field can be measured phase locked to both the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high-response pressure transducers. By a physically plausible explanation for the experimental results, a model for the flow mechanism of the short-length-scale stall cell has been presented. The distinctive feature of the stall cell structure is on the separation vortex bubble with a leg traveling ahead of the rotor, with changing the blade in turn on which the vortex leg stands.

Computation and Measurement of the Flow in Axial Flow Fans With Skewed Blades

Abstract: A numerical analysis of the flow in axial flow fans with skewed blades has been conducted to study the three-dimensional flow phenomena pertaining to this type of blade shape. The particular fans have a low pressure rise and are designed without stator. Initial studies focused on blades skewed in the circumferential direction, followed by investigations of blades swept in the direction of the blade chord. A Navier-Stokes code was used to investigate the flow. The simulation results of several fans were validated experimentally. The three-dimensional velocity field was measured in the fixed frame of reference with a triple sensor hot-film probe. Total pressure distribution measurements were performed with a fast response total pressure probe. The results were analyzed, leading to a design method for fans with swept blades. Forward swept fans designed accordingly exhibited good aerodynamic performance. The sound power level, measured on an acoustic fan test facility, improved.

An overview of rotating stall and surge control for axial flow compressors

Abstract: Modeling and control for axial flow compression systems have received great attention in recent years. The objectives are to suppress rotating stall and surge, to extend the stable operating range of the compressor system, and to enlarge domains of attraction of stable equilibria using feedback control methods. The success of this research field will significantly improve compressor performance and thus future aeroengine performance. This paper surveys the research literature and summarizes the major developments in this active research field, focusing on the modeling and control perspectives to rotating stall and surge for axial flow compressors.

Deflector for controlling entry of cooling air leakage into the gaspath of a gas turbine engine

Abstract: The invention provides a deflector for redirecting cooling air leakage to improve the efficiency of a gas turbine engine. A conventional gas turbine engine includes a forward stator assembly and a rotor assembly with an air cooled rotor disc, and a circumferential array of blade retention slots. An array of air cooled rotor blades with blade bases are retained in each slot. The rotor blades are disposed equidistantly about the circumference of the rotor disc with a radially extending gap between each adjacent rotor blade. It is the significant detrimental effect of cooling air leakage into these gaps, which is the focus of this invention. The invention relates to providing a deflector, disposed circumferentially on a forward face of the coverplate, for deflecting cooling air leakage, flowing from the running seal through the cooling air leakage path, away from the gaps between the blades, onto the outward surface of the blade platform, and into the gaspath at an acute angle relative to rearwardly axial flow therein.

Development of Advanced Compressor Airfoils for Heavy-Duty Gas Turbines: Part I — Design and Optimization

Abstract: A new family of subsonic compressor airfoils, which are characterized by low losses and wide operating ranges, has been designed for use in heavy-duty gas turbines. In particular the influence of the higher airfoil Reynolds numbers compared to aeroengine compressors and the impact of these differences on the location of transition are taken into account. The design process itself is carried out by the combination of a geometric code for the airfoil description, with a blade-to-blade solver and a numerical optimization algorithm. The optimization process includes the design-point losses for a specified Q3D flow problem and the off-design performance for the entire operating range. The family covers a wide range of inlet flow angle, Mach number, flow turning, blade thickness, solidity and AVDR in order to consider the entire range of flow conditions that occur in practical compressor design. The superior performance of the new airfoil family is demonstrated by a comparison with conventional controlled diffusion airfoils (CDA). The advantage in performance has been confirmed by detailed experimental investigations, which will be presented in Part II of the paper. This leads to the conclusion that CDA airfoils that have been primarily developed for aeroengine applications are not the optimum solution, if directly transferred to heavy-duty gas turbines. A significant improvement in compressor efficiency is possible, if the new profiles are used instead of conventional airfoils. @S0889-504X~00!02102-4#

The Influence of Shrouded Stator Cavity Flows on Multistage Compressor Performance

Abstract: Experiments were performed on a low-speed multistage axial-flow compressor to assess the effects of shrouded stator cavity flows on aerodynamic performance. Five configurations, which involved systematic changes in seal-tooth leakage rates and/or elimination of the shrouded stator cavities, were tested. Rig data indicate increasing seal-tooth leakage substantially degraded compressor performance. For every 1 percent increase in seal-tooth clearance-to-span ratio, the decrease in pressure rise was 3 percent and the reduction in efficiency was 1 point. These observed performance penalties are comparable to those commonly reported for rotor and cantilevered stator tip clearance variations. The performance degradation observed with increased leakage was brought about in two distinct ways. First, increasing seal-tooth leakage directly spoiled the near-hub performance of the stator row in which leakage occurred. Second, the altered stator exit flow conditions, caused by increased leakage, impaired the performance of the next downstream stage by decreasing the work input of the rotor and increasing total pressure loss of the stator. These trends caused the performance of downstream stages to deteriorate progressively. Numerical simulations of the test rig stator flow field were also conducted to help resolve important fluid mechanic details associated with the interaction between the primary and cavity flows. Simulationmore » results show that fluid originating in the upstream cavity collected on the stator suction surface when the cavity tangential momentum was low and on the pressure side when it was high. The convection of cavity fluid to the suction surface was a mechanism that reduced stator performance when leakage increased.« less

Development of Advanced Compressor Airfoils for Heavy-Duty Gas Turbines: Part II — Experimental and Theoretical Analysis

Abstract: In Part I of this paper a family of numerically optimized subsonic compressor airfoils for heavy-duty gas turbines, covering a wide range of flow properties, is presented. The objective of the optimization was to create profiles with a wide low loss incidence range. Therefore, design point and off-design performance had to be considered in an objective function. The special flow conditions in large-scale gas turbines have been taken into account by performing the numerical optimization procedure at high Reynolds numbers and high turbulence levels. The objective of Part II is to examine some of the characteristics describing the new airfoils, as well as to prove the reliability of the design process and the flow solver applied. Therefore, some characteristic members of the new airfoil series have been extensively investigated in the cascade wind tunnel of DLR cologne. Experimental and numerical results show profile Mach number distributions, total pressure losses, flow turning, and static pressure rise for the entire incidence range. The design goal with low losses and especially a wide operating range could be confirmed, as well as a mild stall behavior. Boundary layer development, particularly near stall condition, is discussed using surface flow visualization and the results of boundary layer calculations. An additional experimental study, using liquid crystal coating, provides necessary information on suction surface boundary-layer transition at high Reynolds numbers. Finally, results of Navier‐Stokes simulations are presented that enlighten the total pressure loss development and flow turning behavior, especially at high incidence in relation to the results of the design tool.@S0889-504X~00!02602-7#

Axial flow compressor design

Abstract: The purpose of this paper is to set out some of the basic principles and rules associated with the design of axial flow compressors, principally for aero-engines, as well as the practical c...

Transonic fan and compressor design

Abstract: Transonic fans and compressors are now widely used in gas turbine engines because of their benefits in terms of compactness and reduced weight and cost. However, careful and precise design is essential if high levels of performance are to be achieved. In this paper, the evolution of transonic compressor designs and methods is outlined, followed by more detailed descriptions of current compressor configurations and requirements and modern aerodynamic design methods and philosophies.Current procedures employ a range of methods to allow the designer to refine a new design progressively. Overall parameters, such as specific flow and mean stage loading, the axial matching between the stages at key operating conditions and the radial matching between the blade rows are set in turn, using one- and two-dimensional techniques. Finally, detailed quasi-three-dimensional and three-dimensional computational fluid dynamics (CFD) analyses are employed to refine the design. However, it is important to appreciate ...

Aerodynamic Analysis of Multistage Turbomachinery Flows in Support of Aerodynamic Design

Abstract: This paper summarizes the state of 3D CFD based models of the time average flow field within axial flow multistage turbomachines. Emphasis is placed on models which are compatible with the industrial design environment and those models which offer the potential of providing credible results at both design and off-design operating conditions. The need to develop models which are free of aerodynamic input from semi-empirical design systems is stressed. The accuracy of such models is shown to be dependent upon their ability to account for the unsteady flow environment in multistage turbomachinery. The relevant flow physics associated with some of the unsteady flow processes present in axial flow multistage machinery are presented along with procedures which can be used to account for them in 3D CFD simulations. Sample results are presented for both axial flow compressors and axial flow turbines which help to illustrate the enhanced predictive capabilities afforded by including these procedures in 3D CFD simulations. Finally, suggestions are given for future work on the development of time average flow models.Copyright © 1999 by ASME

Mixing enhancement using axial flow

Abstract: A method and an apparatus for enhancing fluid mixing. The method comprises the following: (a) configuring a duct to have an effective outer wall, an effective inner wall, a cross-sectional shape, a first cross-sectional area and an exit area, the first cross-sectional area and the exit area being different in size; (b) generating a first flow at the first cross-sectional area, the first flow having a total pressure and a speed equal to or greater than a local speed of sound; and (c) generating a positive streamwise pressure gradient in a second flow in proximity of the exit area. The second flow results from the first flow. Fluid mixing is enhanced downstream from the duct exit area.

Cryogenic air separation system with integrated machine compression

Abstract: A cryogenic air separation system wherein base load pressure energy is supplied to the feed air by a base load compressor and custom load pressure energy is supplied to the feed air by a bridge machine having one or more turbine booster compressors and one or more product boiler booster compressors, all of the compressors of the bridge machine driven by power supplied through a single gear case.

Hybrid compressor and control method

Abstract: A hybrid compressor selectively driven by an engine and an electric motor. The hybrid compressor includes a variable displacement compression mechanism. When the compression mechanism is driven by the motor, the cooling capacity of a refrigeration circuit that includes the hybrid compressor is adjusted by controlling the inclination of the swash plate and the motor speed. In the control procedure, the inclination angle of the swash plate and the motor speed are controlled so that the compression mechanism and the motor are most efficiently operated to achieve the required cooling capacity. Therefore, the hybrid compressor is constantly operated with maximum efficiency.

Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 1—Framework of Technical Approach and Wake–Stator Blade Interactions

Abstract: In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stators with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flowfield showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceivedmore » by the stator in the same manner as a wake. In Part 1, the focus will be on the framework of technical approach, and the interaction of stator with the moving upstream rotor wakes.« less

Nonlinear robust disturbance rejection controllers for rotating stall and surge in axial flow compressors

Abstract: We develop globally stabilizing robust/disturbance rejection controllers for rotating stall and surge in axial flow compressors with uncertain system dynamics and exogenous disturbances. Specifically, using the nonlinear-nonquadratic disturbance rejection optimal control framework for systems with bounded energy (square-integrable) L/sub 2/ disturbances developed in Haddad et al. (1997) and the nonlinear-nonquadratic robust optimal control framework for systems with nonlinear structured parametric uncertainty developed in Haddad et al. (1997), a family of globally robustly stabilizing controllers for jet engine compression systems is developed. The proposed controllers are compared with locally stabilizing bifurcation-based controllers and recursive backstepping controllers.

Rotor blade an axial-flow engine

Abstract: A rotor blade airfoil of an axial-flow turbomachine, for a fan or a compressor high-pressure stage of a gas turbine system, configured in the tip area to improve supersonic performance. The blade afflux edge has a forward-back sweep. The tip region of the blade efflux edge can be designed essentially similar to the blade afflux edge, with the tip region extending across the outer 15% to 25% of the blade span.

Prediction and Measurement of Rotating Stall Cells in an Axial Compressor

Abstract: This paper presents a parallel numerical and experimental study of rotating stall cells in an axial compressor. Based on previous theoretical and experimental studies stressing the importance of fluid inertia and momentum exchange mechanisms in rotating stall, a numerical simulation using the Euler equations is conducted. Unsteady two-dimensional solutions of rotating stall behavior are obtained in a one-stage low subsonic axial compressor. The structure and speed of propagation of one fully developed rotating stall cell together with its associated unsteady static pressure and throughflow field distributions are presented. The numerical capture of a stalled flow region starting from a stable high-flow operating point with an axisymmetric flow distribution and evolving at a reduced mass flow operating point into a rotating stall pattern is also discussed. The experimental data (flow visualization, time-averaged and unsteady row-by-row static pressure measurements) acquired in a four-stage water model of a subsonic axial compressor cover a complete characteristic line ranging from high mass flow in the stable regime to zero throughflow. Stall inception is presented together with clearly marked different operating zones within the unstable regime. For one operating point in the unstable regime, the speed of propagation of the cell as well as the static pressure spikes at the front and rear boundaries of the rotating stall cell are compared between computations, measurements, and an idealized theory based on momentum exchange between blade rows entering and leaving the stalled cell. In addition, the time evolution of the pressure trace at the rotor/stator interface is presented. This study seems to support the assumption that the cell structure and general mechanism of full-span rotating stall propagation are essentially governed by inertial effects and momentum exchange between the sound and stalled flow at the cell edges.

Method of operation of a gas turbine engine and a gas turbine engine

Abstract: A gas turbine engine that has a turbine ( 1 ) mounted downstream of a combustor ( 5 ), a compressor turbine ( 2 ) mounted downstream of turbine ( 1 ) for producing power for driving a compressor ( 3 ), a heat exchanger ( 6 ) having a first circuit ( 6 1 ) connected to compressor turbine ( 2 ) and a second circuit ( 6 2 ) connected between compressor ( 2 ) and turbine ( 1 ) and a fluid discharge device ( 7 ) between compressor ( 3 ) and combustor ( 5 ). The gas turbine engine has a reactor ( 8 ) that has a heating device ( 9 ), inlets (F, W) connected to sources of fuel and water and an outlet connected to combustor ( 5 ). Heating device ( 9 ) is connected the outlet of compressor turbine ( 2 ). The engine also has a system for keeping the temperature at the outlet of compressor turbine ( 2 ) constant.

Liquid-liquid extraction based on a new flow pattern: Two-fluid Taylor-Couette flow

Abstract: The exploitation of flow instabilities that can occur in rotating flows is investigated as a new approach to liquid-liquid extraction Two immiscible liquids are radially stratified by centrifugal force in the annulus between corotating coaxial cylinders When the inner cylinder is then rotated above a critical speed, Taylor vortices form in one or both of the fluids Although the flow pattern yields a relatively small amount of interfacial surface area, the surface is highly active for interphase mass transfer due to the local vortex motion With the addition ii of countercurrent axial flow, efficient continuous processing is also possible It is proposed that this two-fluid Taylor-Couette flow yields a viable extraction process, particularly for fluid pairs that are easily emulsifiable and therefore have limited processing options with the current commercially available equipment With this goal, the present study of two-fluid Taylor-Couette flow with countercurrent axial flow includes: • A review of aqueous-aqueous and reversed micelle extraction techniques, the commercially available centrifugal extractors, and one fluid TaylorCouette flow and its variations • A theoretical analysis to predict the onset of the two-fluid Taylor-Couette instability in the presence of countercurrent axial flow • Theoretical predictions for interphase mass transfer using a combination of penetration theory and computational fluid dynamics • The demonstration of two-fluid Taylor-Couette flow with countercurrent axial flow in the laboratory, including: (1) fluid mechanics studies to determine the onset of two-fluid Taylor-Couette flow, and (2) mass transfer studies to determine intraphase and interphase mass transfer characteristics The agreement between the theoretical analyses and the experimental results is good for both the fluid mechanics and the mass transfer Furthermore, the iii extraction performance of two-fluid Taylor-Couette flow with countercurrent axial flow is very promising with the mass transfer coefficient proportional to the strength of Taylor vortices This suggests that very high extraction efficiencies can be obtained with even larger relative rotation rates or cylinder modification to promote vortex formation Besides two-fluid Taylor-Couette flow, other instabilities can occur that degrade the extraction performance and should be avoided in the design and operation of an extractor With low viscosity fluids at low rotation rates, twofluid Taylor-Couette flow is not observed experimentally, but rather the barber pole pattern, which is believed to be a lingering gravitational effect At high countercurrent axial flowrates, the linear stability analysis predicts a KelvinHelmholtz instability related to the countercurrent flow profile When axial flow is not present, two computational fluid dynamics packages calculate that vortices paired across the interface can corotate, rather than counterrotate, with each other

Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 2—Rotor Tip Vortex/Streamwise Vortex–Stator Blade Interactions

Abstract: In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stator with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flowfield showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 2, the focus will be on the interaction of stator with the moving upstream rotor tip and streamwise vortices, the controlling parametric trends, and implications on design.

Airflow guide stator vane for axial flow fan and shrouded axial flow fan assembly having such airflow guide stator vanes

Abstract: An airflow guide stator vane for an axial flow fan and a shrouded axial flow fan assembly having such stator vanes are disclosed. The airflow guide stator vane has a leading edge line, a trailing edge line, and an airflow guide surface extending from the leading edge line to the trailing edge line. The stator vane is radially positioned in an axial flow fan and is curved so that its leading edge line is perpendicular to oblique velocity components of an airflow each of which is a sum vector of a rotation-directional velocity component and a radius-directional component of an air particle of the airflow. The axial flow fan assembly comprises an axial flow fan and a shroud. The axial flow fan consists of a circular central hub connected with a driving shaft of a motor and a plurality of blades radially arranged along the circumference of the hub. The shroud consists of a housing surrounding the peripheral ends of said axial flow fan and forming an airflow passage, a motor support being positioned at its center portion and holding a motor for driving said axial flow fan, and the above-described stator vanes.

Modeling Shrouded Stator Cavity Flows in Axial-Flow Compressors

Abstract: Experiments and computational analyses were completed to understand the nature of shrouded stator cavity flows From this understanding, a one-dimensional model of the flow through shrouded stator cavities was developed This model estimates the leakage mass flow, temperature rise, and angular momentum increase through the cavity, given geometry parameters and the flow conditions at the interface between the cavity and primary flow path This cavity model consists of two components, one that estimates the flow characteristics through the labyrinth seals and the other that predicts the transfer of momentum due to windage A description of the one-dimensional model is given The incorporation and use of the one-dimensional model in a multistage compressor primary flow analysis tool is described The combination of this model and the primary flow solver was used to reliably simulate the significant impact on performance of the increase of hub seal leakage in a twelve-stage axial-flow compressor Observed higher temperatures of the hub region fluid, different stage matching, and lower overall efficiencies and core flow than expected could be correctly linked to increased hub seal clearance with this new technique The importance of including these leakage flows in compressor simulations is shown

Periodic transition on an axial compressor stator : Incidence and clocking effects : Part I : Experimental data

Abstract: Periodic wake-induced transition on the outlet stator of a 1.5-stage axial compressor is examined using hot-film arrays on both the suction and pressure surfaces. The time-mean surface pressure distribution is varied by changing the blade incidence, while the free-stream disturbance field is altered by clocking of the stator relative to an inlet guide vane row. Ensemble-averaged plots of turbulent intermittency and relaxation factor (extent of calmed flow following the passage of a turbulent spot) are presented. These show the strength of periodic wake-induced transition phenomena to be significantly influenced by both incidence and clocking effects. The nature and extent of transition by other modes (natural, bypass, and separated flow transition) are altered accordingly. Leading edge and midchord separation bubbles are affected in a characteristically different manner by changing free-stream periodicity. There are noticeable differences between suction and pressure surface transition behavior, particularly as regards the strength and extent of calming. In Part II of this paper, the transition onset observations from the compressor stator are used to evaluate the quasi-steady application of conventional transition correlations to predict unsteady transition onset on the blading of an embedded axial compressor stage.