Showing papers on "Axial compressor published in 2006"

Secondary Flows in Axial Turbines—A Review

Abstract: An important problem that arises in the design and the performance of axial flow turbines is the understanding, analysis, prediction and control of secondary flows. Sieverding1 has given a review of secondary flow literature, covering up to 1985. In this paper a brief review of pre-1985 work is given, and then a survey of open literature secondary flow investigations since the Sieverding review is presented. Most of the studies reviewed deal with plane or annular cascade flows. Tip clearance effects are not covered. The basic secondary flow picture for a turbine cascade, as measured and verified by a number of investigators is described. Recent work that shows refined secondary flow vortex structures is examined. A flow parameter based on inlet boundary layer properties used to predict horseshoe vortex swirl is presented. Work on secondary flow loss reduction, involving airfoil geometry, endwall fences and endwall contouring is briefly reviewed. A new leading edge bulb geometry that has demonstrated impressive loss reduction is considered. It is concluded that accurate routine prediction of secondary flow losses has not yet been achieved, and must await either a better turbulence model or more experiments to reveal new endwall loss production mechanisms. Lastly, loss is examined from the standpoint of entropy generation.

A Criterion for Axial Compressor Hub-Corner Stall

Abstract: This paper presents a new criterion for estimating the onset of three-dimensional hub-corner stall in axial compressor rotors and shrouded stators. A simple first-of-a-kind description of hub-corner stall formation is developed which consists of (i) a stall indicator, which quantifies the extent of the separated region via the local blade loading and thus indicates whether hub-corner stall occurs, and (ii) a diffusion parameter, which defines the diffusion limit for unstalled operation. The stall indicator can be cast in terms of a Zweifel loading coefficient. The diffusion parameter is based on preliminary design flow variables and geometry. Computational simulations and single and multistage compressor data are used to show the applicability of the criterion over a range of blade design parameters. The criterion also enables determination of specific flow control actions to mitigate hub-corner stall. As an illustration, a flow control blade, designed using the ideas developed, is seen to produce a substantial reduction in the flow nonuniformity associated with hub-corner stall.

Short Length-Scale Rotating Stall Inception in a Transonic Axial Compressor: Criteria and Mechanisms

Abstract: The current paper reports on investigations aimed at advancing the understanding of the flow mechanism that leads to the onset of short-length scale rotating stall in a transonic axial compressor. Experimental data show large oscillation of the tip clearance vortex as the rotor operates near the stall condition. Inception of spike-type rotating stall is also measured in the current transonic compressor with high response pressure transducers. Computational studies of a single passage and the full annulus were carried out to identify flow mechanisms behind the spike-type stall inception in the current transonic compressor rotor. Steady and unsteady single passage flow simulations were performed, first to get insight into the interaction between the tip clearance vortex and the passage shock. The conventional Reynolds-averaged Navier-Stokes method with a standard turbulence closure scheme does not accurately reproduce tip clearance vortex oscillation and the measured unsteady pressure field. Consequently, a Large Eddy Simulation (LES) was carried out to capture more relevant physics in the computational simulation of the rotating stall inception. The unsteady random behavior of the tip clearance vortex and it’s interaction with the passage shock seem to be critical ingredients in the development of spike-type rotating stall in a transonic compressor. The Large Eddy Simulation was further extended to the full annulus to identify flow mechanisms behind the measured spike-type rotating stall inception. The current study shows that the spike-type rotating stall develops after the passage shock is fully detached from the blade passages. Interaction between the tip clearance vortex and the passage shock creates a low momentum area near the pressure side of the blade. As the mass flow rate decreases, this low momentum area moves further upstream and reversed tip clearance flow is initiated at the trailing edge plane. Eventually, the low momentum area near the pressure side reaches the leading edge and forward spillage of the tip clearance flow occurs. The flows in the affected blade passage or passages then stall. As the stalled blade passages are formed behind the passage shock, the stalled area rotates counter to the blade rotation just like the classical Emmon’s type rotating stall. Both the measurements and the computations show that the rotating stall cell covers one to two blade passage lengths and rotates at roughly 50% of the rotor speed.Copyright © 2006 by ASME

Principles of turbomachinery in air-breathing engines

Abstract: 1. Introduction to gas turbine engines 2. Overview of turbomachinery nomenclature 3. Aerothermodynamics of turbomachines 4. Energy transfer between a fluid and a rotor 5. Dimensional analysis, maps and specific speed 6. Radial equilibrium theory 7. Polytropic (small-stage) efficiency 8. Axial-flow turbines 9. Axial-flow compressors 10. Radial inflow turbines 11. Centrifugal compressors 12. Turbine-compressor matching.

Axial-Flow Turbines

Abstract: This chapter focuses on axial-flow turbines that are the most widely employed turbines using a compressible fluid Axial-flow turbines power most of the gas turbine units and they are more efficient than radial-inflow turbines in most operational ranges They are also used in steam turbine design; however, there are some significant differences between the axial-flow turbine design for a gas turbine and the design for a steam turbine Axial-flow turbines are now designed with a high work factor to obtain lower fuel consumption and reduce the noise from the turbine Lower fuel consumption and lower noise requires the design of higher by-pass ratio engines, and a high by-pass ratio engine in turn requires various turbine stages to drive the high-flow, low-speed fan The flow in axial-flow turbines enters and leaves in the axial direction There are two types of axial turbines: impulse type and reaction type Most axial flow turbines consist of more than one stage The front stages are usually impulse (zero reaction) and the later stages have about 50% reaction The impulse stages produce about twice the output of a comparable 50% reaction stage, while the efficiency of an impulse stage is less than that of a 50% reaction stage The high temperatures that are available in the turbine section have resulted from the improvements of the metallurgy of the blades in the turbines Development of directionally solidified blades as well as the new single-crystal blades, with the new coating cooling schemes, is responsible for the increase in firing temperatures The high pressure ratio in the compressor also causes the cooling air used in the first stages of the turbine to become hot

Numerical Studies of the Effects of Active and Passive Circulation Enhancement Concepts on Wind Turbine Performance

Abstract: The aerodynamic performance of a wind turbine rotor equipped with circulation enhancement technology (trailing edge blowing or Gurney flaps) is investigated using a three-dimensional unsteady viscous flow analysis. The National Renewable Energy Laboratory (NREL) Phase VI horizontal axis wind turbine (HAWT) is chosen as the baseline configuration. Experimental data for the baseline case is used to validate the flow solver, prior to its use in exploring these concepts. Calculations have been performed for axial and yawed flow at several wind conditions. Results presented include radial distribution of the normal and tangential forces, shaft torque, root flap moment, and surface pressure distributions at selected radial locations. At low wind speed (7 m/s) where the flow is fully attached, it is shown that a Coanda jet at trailing edge is effective at increasing circulation resulting in an increase of lift and the chordwise thrust force. This leads to an increased amount of net power generation compared to the baseline configuration for moderate blowing coefficients (Cμ ≤ 0.075). A passive Gurney flap was found to increase the bound circulation and produce increased power in a manner similar to Coanda jet. At high wind speed (15 m/s) where the flow is separated, both the Coanda jet and Gurney flap become ineffective. The effects of these two concepts on the root bending moments have also been studied.

Causes of Acoustic Resonance in a High-Speed Axial Compressor

Abstract: Nonharmonic acoustic resonance was detected in the static pressure and sound signals in a four-stage high-speed axial compressor when the compressor was operating close to the surge limit. Based on prior research reported in the literature and measurements of the resonance frequency, Mach number of the mean flow, and the axial and circumferential phase shifts of the pressure signal during resonance, it is shown that the acoustic resonance is an axial standing wave of a spinning acoustic mode with three periods around the circumference of the compressor. This phenomenon occurs only if the aerodynamic load in the compressor is high, because the mode needs a high circumferential Mach number for resonance conditions. Mathematics of existing analyses of acoustic resonances in turbomachinery complex and have therefore rarely resulted in published examples of good agreement with real engine data. The present paper provides suitable, physically based simplifications of the existing mathematical models which are applicable for modes with circumferential wavelengths of more than two blade pitches and resonance frequencies considerably higher than the rotor speed.

Optimisation of sensor arrays for radial mode analysis in flow ducts

Abstract: For the assessment and improvement of noise reduction concepts and the validation of computational aero-acoustic (CAA) codes in turbomachinery applications, the detailed knowledge of the in-duct acoustic mode spectrum of tonal frequency components is of great interest. Radial mode analysis (RMA) is an experimental technique that delivers the complex amplitudes of higher order acoustic modes propagating through flow ducts. Thus, RMA enables the calculation of the acoustic power radiated in and against flow direction, though, requiring at high frequencies the acquisition of the sound field at a large number of positions in the flow duct. The quality of the analysis results is very sensitive to the arrangement of the measurement coordinates, the frequency, and the flow parameters. A simple and robust RMA realisation just consists of sensor rakes at a single duct cross section. This method, however, has the drawback of not being able to distinguish downstream and upstream propagating modes. Furthermore, the sound field as well as the flow field may be altered by the rakes. In the paper, a numerical study of RMA employing four substantially different sensor arrangements is conducted. The arrangements I and II consist of sensor rakes located at two or four axial measurement positions, respectively. Arrangement III is equipped with sensors mounted flush with the hub and the outer duct wall and in arrangement IV the sensors are mounted flush with the outer duct wall, only. The dependency of the RMA quality on the frequency, e.g. the number of cut-on modes, and on the number of axial and radial measurement positions was investigated by means of a condition analysis. Studies were carried out for the analysis of coherent modal sound fields in hard-walled cylindrical flow ducts of arbitrary hub-to-tip ratio with a constant mean axial flow profile. Additionally, the influence of a solid-body like swirl was considered. The paper reveals reasons for bad conditioning of the RMA-systems and gives guidelines for an optimum sensor separation in order to improve the overall system condition. Since the condition number is only a relative measure for the inaccuracies caused by the RMA system, simulations with synthetic sound pressure data were carried out. The RMA performance of the sensor arrangements I-IV is compared.

Axial compressor blading

Abstract: An axial compressor has at least one circumferential row of aerofoil members (30a, 30b, 30c) in which at least one of the two end walls (37) between adjacent blades is given a non-axisymmetric profile, defined by circumferentially-extending sinusoids at a number of axial positions (AA, BB, CC). Corresponding points on the successive sinusoids are joined by spline curves, so that the curvature of the end wall is smooth. This end-wall profiling modifies the boundary layer flow at the wall, reducing or eliminating the corner separation and reversed flow associated with known arrangements.

Enhancement of Mass Transfer in a Spray Tower Using Swirling Gas Flow

Abstract: Spray towers are commonly used in the chemical and process industries for a number of applications including absorption, desorption and humidification. However, the main disadvantage of a spray tower compared with that of a packed tower is its lower contact efficiency. The present study is concerned with the enhancement of mass transfer between a continuous gas phase and liquid droplets in a spray tower by imparting swirl to the axial gas flow through the tower. It is well known that swirling flow has the ability to augment the rates of heat and mass transfer. Experimental investigations into the hydrodynamics and mass transfer in a laboratory-scale spray tower for air-NH3/H2O system using axial and swirling gas flows have been carried out. The hydrodynamic studies included measurements of the gas velocity distributions and overall pressure drop in the tower, and characterization of water sprays generated by a pressure-swirl nozzle where radial liquid distributions, droplet size and its distribution and mean droplet size in terms of SMD were measured. As for the mass transfer performance of the spray tower, the effect of the gas and liquid flow rates on the overall gas phase mass transfer coefficient, Kga, was investigated for both swirling and non-swirling axial gas flows in order to quantify the effect of swirl. It has been found that Kga increases with increasing gas/liquid flow rates and imparting swirl in the gas flow enhances Kga up to 20% compared with that in axial flows. Correlations of Kga as a function of the gas/liquid flow rates, and also as a function of the gas flow rate and initial droplets SMD are developed. A design methodology to determine the height of a spray tower required to achieve a specified amount of removal of a solute from a gas mixture is proposed.

Interaction of Tip Clearance Flow and Three-Dimensional Separations in Axial Compressors

Abstract: This paper considers the interaction of tip clearance flow with three-dimensional (3D) separations in the corner region of a compressor cascade. Three-dimensional numerical computations were carried out using ten levels of tip clearance, ranging from zero to 2.18% of blade chord. The 3D separations on the blade suction surface were largely removed by the clearance flow for clearance about 0.58% of chord. For this cascade, experimental results at zero and 1.7% chord tip clearance were used to assess the validity of the numerical predictions. The removal mechanism was associated with the suppression of the leading edge horseshoe vortex and the interaction of tip clearance flow with the endwall boundary layer, which develops into a secondary flow as it is drifted towards the blade suction surface. Such interaction leads to the formation of a new 3D separation line on the endwall. The separation line forms the base of a separated stream surface which rolls up into the clearance vortex.Copyright © 2006 by ASME

Application of SPIV in turbomachinery

Abstract: Stereoscopic particle-image velocimetry (SPIV) has been successfully used in a low-speed large-scale axial compressor. A configuration in which two CCD cameras were placed at different sides of the light sheet was employed. It is demonstrated that the results measured with such a configuration are significant for the study of unsteady flow structures of the streamwise vortices and secondary flows in the test rotor, and that such a configuration is easy to use in multi-stage turbomachinery. The instantaneous snapshots, ensemble-averaged results and turbulence statistics in the rotor passage were obtained at both the design and near-stall conditions. The representative flow structures, such as the tip leakage vortex, the corner vortex and the inlet guide vane wake, can be depicted clearly. Moreover, according to experimental and theoretical analyses, some guidance is provided for the application of SPIV in turbomachinery.

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines

Abstract: Foreword. Preface. Part 1: Flutter-Flutter boundaries for pairs of low pressure turbine blades-Influence of a vibration amplitude-A method to assess flutter stability of complex modes-Flutter design of low pressure turbine blades with cyclic symmetric modes-Experimental and numerical investigation of 2D palisade flutter for the harmonic oscillations-Possibility of active cascade flutter control with smart structure in transonic flow condition-Experimental flutter investigations of an annular compressor cascade: influence of reduced frequency on stability.- Part 2: Forced responses-Unsteady gust response in the frequency domain-Axial turbine blade vibrations induced by the stator flow-Mistuning and coupling effects in turbomachinery bladings-Evalution of the principle of aerodynamic superposition in forced response calculations-Comparison of models to predict low engine order excitation in a high pressure turbine stage-Experimental reduction of transonic fan forced response by IGV flow control.- Part 3: Multistage effects-Unsteady aerodynamic work on oscillating annular cascades in counter rotation-Stucture of unsteady vortical wakes behind blades of mutual-moving rows of an axial turbomachine-The effect of mach number on LP turbine wake-blade interaction-Multistage coupling for unsteady flows in turbomachinery- Part 4: Aeroacoustics- Passive noise control by vane lean and sweep-Interaction of acoustic and vortical disturbances with an annular cascade in a swirling flow-Influence of mutual circumferential shift of stators on the noice generated by systems of rows stator-rotor-stator of the axial compressor-A frequency-domain solver for the non-linear propagation and radiation of fan noise- Part 5: Flow instabilities-Analysis of unsteady casing-Core compressor rotating stall simulation with a multi-bladerow model-Parametric study of surface roughness and wake unsteadiness on a flat plate with large pressure gradient-Bypass flow pattern changes at turbo-ram transient operation of combined cycle engine-Experimental investigation of wake-induced transition in a highly loaded linear compressor cascade-Experimental off-design investigation of unsteady secondary flow phenomena in a three-stage axial compressor at 100% nomial speed-Analyses of URANS and LES- Part 6: Computational techniques-Frequency and time domain-Study of shock movement and unsteady pressure on 2D generic model-Numerical unsteady aerodynamics for turbomachinery aeroelasticity-Development of an efficient and robust linearised navier-stokes flow solver-Optimized dual-time stepping technique for time-accurate navier-stokes calculations- Part 7: Experimental unsteady aerodynamics-Experimental and numerical study of nonlinear interactions in two-dimensional transonic nozzle flow-Interaction between shock waves and cascaded blades-Measured and calculated unsteady pressure field in a vaneless diffuser of a centrifugal compressor-DPIV measurements of the flow field between a transonic rotor and an upstream stator-Unsteady pressure management with correction on tubing distortion- Part 8: Aerothermodynamics-Unsteady 3D navier-stokes-Analysis of unsteady aerothermodynamic effects in a turbine-combustor- Part 9: Rotor stator interaction-Stator-rotor aeroelastic interaction for the turbine last stage in 3D transonic flow-Effects of stator clocking in systems of rows-Rotor-stator interaction in a highly loaded, single-stage, unsteady measurments in the rotor relative frame-Two-stage turbine experimental investigations of unsteady stator-to-stator interaction.

Numerical Study of Unsteady Flows in a Scroll Compressor

Abstract: Since scroll compressors contain gas pockets whose shapes and sizes change continuously, the flow fields inside the compressors are time dependent and three-dimensional. The spatial and temporal variations inside the gas pockets also induce unsteady flows between the gas pockets. This unsteadiness controls the mechanisms responsible for the behavior of the scroll compressor components and their interactions. The dynamic nature inherent in the scroll compressors affects the performance and reliability of the scroll compressors. To improve and optimize the scroll compressor design for better performance and reliability, information is needed to understand the detailed physics of the unsteady flows inside the scroll compressors. To provide the fundamental information needed, the unsteady flows in a scroll compressor are studied numerically. The system simulated includes upper bearing housing, scrolls, check valve, and discharge plenum. Refrigerant-22 is used as the working fluid. The unsteady flows inside and between the gas pockets are characterized by the instantaneous distributions of field quantities and the area- and mass-averaged parameters.

Two-shaft turbocharger

Abstract: A turbocharger, having an axial compressor wheel and an axial turbine wheel mounted on a first shaft supported by a housing, and a radial compressor wheel and a radial turbine wheel mounted on a second shaft, the second shaft concentrically extending around the first shaft and being supported by the housing. The housing defines a first duct extending axially from the exducer of the axial compressor to the inducer of the radial compressor, and a second duct extending axially from the exducer of the radial turbine to the inducer of the axial turbine. A plurality of controllable compressor guide vanes extend through the first duct, and a plurality of controllable turbine stator vanes extend through the second duct. The housing is provided with variable diffuser vanes at the exducer of the radial compressor, and with variable turbine vanes at the inducer of the radial turbine. The variable turbine vanes and the turbine stator vanes are controlled to accurately control the rotation rate of the radial and axial turbines. The compressor guide vanes are controlled to minimize surge and maximize choke flow rate.

Experimental Investigation of Flow Control in Compressor Cascades

Abstract: A large part of the total pressure losses in a compressor stage is caused by secondary flow effects like the separation between the wall and the vane i.e., a corner separation. An experimental and numerical investigation in a highly loaded compressor cascade was performed to understand the fluid mechanic mechanism of this corner separation in order to control it by using vortex generators. The experiments were carried out with a compressor cascade at a high-speed test facility at DLR in Berlin. The cascade consisted of five vanes and their profiles represent the cut at 10% of span distance from the hub of the stator vanes of a single stage axial compressor. The experiments were accomplished at Reynolds numbers up to Re = 0.6 × 106 (based on 40 mm chord) and Mach numbers up to M = 0.7. To measure the total pressure losses of the cascade (caused by the corner separation) a wake rake was used. It consisted of 26 pitot probes to measure the total pressure distribution of the outflow and 4 Conrad probes to determine the outflow angles. To detect the separation area on the vane, a flow visualisation technique was used. In addition to the experiments, numerical computations were carried out with the URANS TRACE, which has been developed at DLR for the simulation of steady and unsteady turbomachinery flow. The computations were performed with identical geometrical conditions as in the experiments, including the measured inflow boundary layer conditions at the side walls. The experiments were performed with the aim of controlling the corner separation. In this case, vortex generators as a passive flow control device were used. The vortex generators were attached at the surface of the suction side of the vanes. The flow control device is producing a strong vortex, which enhances the mixing between the main flow and the retarded boundary layer at the side wall. Thus, the corner separation is reduced on the vanes. The experiments were carried out at the peak efficiency (design point) of the cascade in order to optimize the design of the vortex generators for an application in turbomachines.Copyright © 2006 by ASME

Separation control using synthetic vortex generator jets in axial compressor cascade

Abstract: An experimental investigation conducted in a high-speed plane cascade wind tunnel demonstrates that unsteady flow control by using synthetic (zero mass flux) vortex generator jets can effectively improve the aerodynamic performances and reduce (or eliminate) flow separation in axial compressor cascade. The Mach number of the incoming flow is up to 0.7 and most tested cases are at Ma = 0.3. The incidence is 10° at which the boundary layer is separated from 70% of the chord length. The roles of excitation frequency, amplitude, location and pitch angle are investigated. Preliminary results show that the excitation amplitude plays a very important role, the optimal excitation location is just upstream of the separation point, and the optimal pitch angle is 35°. The maximum relative reduction of loss coefficient is 22.8%.

Axial-Flow Compressors

Abstract: This chapter focuses on axial-flow compressors that are mostly used in gas turbine applications of over 5 MW. In these compressors, the flow enters the compressor in an axial direction (parallel with the axis of rotation), and exits from the gas turbine in the same direction. The axial-flow compressor compresses its working fluid by first accelerating the fluid, and then diffusing it to obtain a pressure increase. The fluid is accelerated by a row of rotating airfoils (blades) called the rotor, and then diffused in a row of stationary blades known as stators. The diffusion in the stator converts the velocity increase gained in the rotor to a pressure increase. A compressor consists of several stages. A combination of a rotor followed by a stator makes up a stage in a compressor. An additional row of pitch variable blades, known as Inlet Guide Vanes (IGV), are frequently used at the compressor inlet to ensure that air enters the first-stage rotors at the desired flow angle. These vanes are also pitch variable, and thus can be adjusted to the varying flow requirements of the engine. In addition to the stators, another diffuser at the exit of the compressor consisting of another set of vanes, often known as the Exit Guide Vanes (EGV), further diffuses the fluid and controls its velocity entering the combustors. In an axial-flow compressor, air passes from one stage to the next, each stage raising the pressure slightly. By producing low-pressure increases in the order of 1.1:1 to 1.4:1, very high efficiencies can be obtained. The use of multiple stages permits overall pressure increases of up to 40:1 in some aerospace applications, and a pressure ratio of 30:1 in some industrial applications.

Exit Flow Field and Performance of Axial Flow Fans

Abstract: Flow fields near the exit and the global performance parameters of the various types of axial flow fans are studied with Particle Image Velocimetry and a standard AMCA 210 flow bench. The fans used in this study included the shrouded, shroudless, and winglet-blade types. The velocity vectors, streamlines, vorticity contours, velocity distributions, and performances are presented and discussed. The flow patterns on the radial and axial planes show that a vortex always exists near the exit of the fans at various impeller angles. The experimental results demonstrate that the shrouded fan with winglets has the most stable flow field and the best fan performance.

The Impact of Surface Roughness on Axial Compressor Performance Deterioration

Abstract: Gas turbine performance deterioration can negatively affect overall production capacity of power plants and cause major economic losses. Gas turbines deteriorate from fouling in the compressor section, and online washing is often applied to recover their performance. The success of online washing depends on site-specific issues, and current systems are inconsistent in use and their effectiveness is difficult to test. The objective of this work is to determine the fundamental mechanisms of axial compressor performance deterioration and recovery through online washing.Empirical data from online washing of RB211-24G at an offshore site were analyzed in the initial phase of research. Empirical data from accelerated salt deterioration and online water washing of a GE J85-13 jet engine were unique to this project. First overall compressor deterioration and single stage performance deterioration were measured using inter-stage gas path instrumentation. Secondly, salt deposits were analyzed to characterize the stage surface roughness and fouling distribution. Finally, recovery through online washing was evaluated. Quasi-one-dimensional models were developed for the GE J85-13 to aid in the test data analysis and to verify the applicability of deterioration loss models to fouled compressors.The study shows that detection of compressor deterioration can be hampered by nonlinear sensitivities to fouling. Engine control modes must be accounted for to avoid misreading the deterioration rate and production capacity. Flow rate was found as the most sensitive deterioration parameter in the GE J85-13. Fouling affected all parts of the stage characteristics reducing flow, pressure and head. The models successfully reflected the deterioration mechanisms although the effects of deterioration were under-predicted. This study shows the importance of applying Reynolds corrections to deteriorated compressors.Online washing efficiency is predominantly affected by the water flow rate. Small droplets and low flow rates increase the fouling in the aft stages, and increased injection time cannot compensate for low flow rates. For effective water washing of the entire compressor section the recommended water-to-air ratio is between 0.8 to 2%.The major contributions of this work are presented in four papers contained in the Appendices.

Separated Flow Transition on an LP Turbine Blade With Pulsed Flow Control

Abstract: Flow measurements were made on a highly loaded low pressure turbine blade in a low-speed linear cascade facility. The blade has a design Zweifel coefficient of 1.34 with a peak pressure coefficient near 47% axial chord (mid-loaded). Flow and surface pressure data were taken for Rec = 20,000 with 3% inlet freestream turbulence. For these operating conditions, a large separation bubble forms over the downstream portion of the blade suction surface, extending from 59% to 86% axial chord. A Single-element hotfilm measurements were acquired to clearly identify the role of boundary layer transition in this separated region. Higher-order turbulence statistics were used to identify transition and separation zones. Similar measurements were also made in the presence of unsteady forcing using pulsed vortex generator jets just upstream of the separation bubble (50% cx ). Measurements provide a comprehensive picture of the interaction of boundary layer transition and separation in this unsteady environment. Similarities between pulsed flow control and unsteady wake motion are highlighted.Copyright © 2006 by ASME

Steady Flows in the Slender, Noncircular, Combustion Chambers of Solid Propellant Rockets

Abstract: An analysis of the steady flows with axial vortices in slender, cylindrical, nonaxisymmetric cavities generated by injection from their porous walls is presented. This problem is encountered in the description of the flow in slender combustion chambers of solid-propellant rocket motors associated with the gasification of the solid propellant surrounding the combustion chamber. Nonreacting flow can be described in terms of self-similar solutions of the Navier-Stokes equations and the solution, calculated numerically for noncircular grain configurations, shows strong axial vortices, with a viscous vortex core that has been analyzed asymptotically for large Reynolds numbers. It was found that the important property of the flow, namely, C 1/2 S/Π, where C is a constant determining the axial pressure gradient, S and n are the cross section area and its perimeter, respectively, becomes unexpectedly close to π/2 at large Reynolds numbers, independently on the geometry of the cross section of the cavity. One can suppose that C 1/2 S/Π = π/2 for any cavities in the invicsid limit, a conjecture that also obtained a support from numerical calculations of flows in rectangular cavities generated by injection from their porous walls.

Aerodynamic Instability and Life-Limiting Effects of Inlet and Interstage Water Injection Into Gas Turbines

Abstract: Gas turbine power enhancement technologies, such as inlet fogging, interstage water injection, saturation cooling, inlet chillers, and combustor injection, are being employed by end users without evaluating the potentially negative effects these devices may have on the operational integrity of the gas turbine. Particularly, the effect of these add-on devices, off-design operating conditions, nonstandard fuels, and compressor degradation/ fouling on the gas turbine's axial compressor surge margin and aerodynamic stability is often overlooked. Nonetheless, compressor aerodynamic instabilities caused by these factors can be directly linked to blade high-cycle fatigue and subsequent catastrophic gas turbine failure; i.e., a careful analysis should always proceed the application of power enhancement devices, especially if the gas turbine is operated at extreme conditions, uses older internal parts that are degraded and weakened, or uses nonstandard fuels. This paper discusses a simplified method to evaluate the principal factors that affect the aerodynamic stability of a single-shaft gas turbine's axial compressor. As an example, the method is applied to a frame-type gas turbine and results are presented. These results show that inlet cooling alone will not cause gas turbine aerodynamic instabilities, but that it can be a contributing factor if for other reasons the machine s surge margin is already slim. The approach described herein can be employed to identify high-risk applications and bound the gas turbine operating regions to limit the risk of blade life reducing aerodynamic instability and potential catastrophic failure.

Experimental and numerical investigation of a subsonic compressor with bend-skewed slot-casing treatment

Abstract: On the basis of the test results of discrete axial and blade angle slot casing treatment, a new type of casing treatment was designed for a subsonic axial flow compressor rotor by optimizin...

Apparatus and method for compressor and turbine performance simulation

Abstract: A method and an apparatus for simulating the operation of a pressured air source or sink such as a compressor or a turbine for a vehicle internal combustion engine calculates momentum sources at interfaces in the compressor or the turbine. A model stores steady state values of mass flux and enthalpy change related to rotational speed, inlet pressure and temperature and outlet pressure. The simulation can be an input to an engine control module for controlling the operation of the vehicle engine connected with the compressor or turbine.