Showing papers on "Tip clearance published in 2009"

Computational Fluid Dynamics Analysis of Blade Tip Clearances on Hemodynamic Performance and Blood Damage in a Centrifugal Ventricular Assist Device

Abstract: An important challenge facing the design of turbodynamic ventricular assist devices (VADs) intended for long-term support is the optimization of the flow path geometry to maximize hydraulic performance while minimizing shear-stress-induced hemolysis and thrombosis. For unshrouded centrifugal, mixed-flow and axial-flow blood pumps, the complex flow patterns within the blade tip clearance between the lengthwise upper surface of the rotating impeller blades and the stationary pump housing have a dramatic effect on both the hydrodynamic performance and the blood damage production. Detailed computational fluid dynamics (CFD) analyses were performed in this study to investigate such flow behavior in blade tip clearance region for a centrifugal blood pump representing a scaled-up version of a prototype pediatric VAD. Nominal flow conditions were analyzed at a flow rate of 2.5 L/min and rotor speed of 3000 rpm with three blade tip clearances of 50, 100, and 200 microm. CFD simulations predicted a decrease in the averaged tip leakage flow rate and an increase in pump head and axial thrust with decreasing blade tip clearances from 200 to 50 microm. The predicted hemolysis, however, exhibited a unimodal relationship, having a minimum at 100 microm compared to 50 microm and 200 microm. Experimental data corroborate these predictions. Detailed flow patterns observed in this study revealed interesting fluid dynamic features associated with the blade tip clearances, such as the generation and dissipation of tip leakage vortex and its interaction with the primary flow in the blade-blade passages. Quantitative calculations suggested the existence of an optimal blade tip clearance by which hydraulic efficiency can be maximized and hemolysis minimized.

The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine

Abstract: As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.Copyright © 2009 by ASME

Blade Tip Clearance Flow and Compressor Nonsynchronous Vibrations: The Jet Core Feedback Theory as the Coupling Mechanism

Abstract: This paper investigates the role of tip clearance flow in the occurrence of nonsynchronous vibrations (NSVs) observed in the first axial rotor of a high-speed high-pressure compressor in an aeroengine. NSV is an aeroelastic phenomenon where the rotor blades vibrate at nonintegral multiples of the shaft rotational frequencies in operating regimes where classical flutter is not known to occur. A physical mechanism to explain the NSV phenomenon is proposed based on the blade tip trailing edge impinging jetlike flow, and a novel theory based on the acoustic feedback in the jet potential core. The theory suggests that the critical jet velocity, which brings a jet impinging on a rigid structure to resonance, is reduced to the velocities observed in the blade tip secondary flow when the jet impinges on a flexible structure. The feedback mechanism is then an acoustic wave traveling backward in the jet potential core, and this is experimentally demonstrated. A model is proposed to predict the critical tip speed at which NSV can occur. The model also addresses several unexplained phenomena, or missing links, which are essential to connect tip clearance flow unsteadiness to NSV. These are the pressure level, the pitch-based reduced frequency, and the observed step changes in blade vibration and mode shape. The model is verified using two different rotors that exhibited NSV.

Active tip clearance control arrangement for gas turbine engine

Abstract: An active tip clearance control (ATCC) apparatus of an aircraft gas turbine engine is situated within a pressurized core case of the engine. First and second portions of bypass air flow passing through the respective compressed core compartment and the ATCC apparatus, are isolated from one another in order to improve both the ATCC performance and bypass air duct performance.

Numerical Investigations of the Coupled Flow Through a Subsonic Compressor Rotor and Axial Skewed Slot

Abstract: In order to advance the understanding of the fundamental mechanisms of axial skewed slot casing treatment and their effects on the subsonic axial-flow compressor flow field, the coupled unsteady flow through a subsonic compressor rotor and the axial skewed slot was simulated with a state-of-the-art multiblock flow solver. The computational results were first compared with available measured data, that showed the numerical procedure calculates the overall effect of the axial skewed slot correctly. Then, the numerically obtained flow fields were interrogated to identify the physical mechanism responsible for improvement in stall margin of a modern subsonic axial-flow compressor rotor due to the discrete skewed slots. It was found that the axial skewed slot casing treatment can increase the stall margin of subsonic compressor by repositioning of the tip clearance flow trajectory further toward the trailing of the blade passage and retarding the movement of the incoming/tip clearance flow interface toward the rotor leading edge plane.

Shock/Boundary-Layer/Tip-Clearance Interaction in a Transonic Rotor Blade

Abstract: A newly designed rotor was modeled from the well-known radially stacked NASA rotor 37 by applying a three-dimensional shape to the original blade stacking line. A considerable curvature toward the direction of rotor rotation was given to the new blade. A three-dimensional numerical model, developed and validated using a commercial computational fluid dynamics Reynolds-averaged Navier―Stokes code, was adopted to predict the flowfield inside the new rotor. Steady-viscous-flow calculations were run at the design speed of the baseline configuration. Compared with rotor 37, the new rotor showed a higher efficiency, mainly due to a three-dimensional modification of the shock structure. At the outer span, the new rotor developed a blade-to-blade shock front located more downstream than in the baseline rotor, with a considerable impact on the flowfield near the casing. Computational fluid dynamics flow visualizations showed a less detrimental shock/boundary-layer/tip-clearance interaction at low-flow operating conditions, with a considerable reduction of the low-momentum-fluid region after the shock.

Parametric study of blade tip clearance, flow rate, and impeller speed on blood damage in rotary blood pump.

Abstract: Phenomenological studies on mechanical hemolysis in rotary blood pumps have provided empirical relationships that predict hemoglobin release as an exponential function of shear rate and time. However, these relations are not universally valid in all flow circumstances, particularly in small gap clearances. The experiments in this study were conducted at multiple operating points based on flow rate, impeller speed, and tip gap clearance. Fresh bovine red blood cells were resuspended in phosphate-buffered saline at about 30% hematocrit, and circulated for 30 min in a centrifugal blood pump with a variable tip gap, designed specifically for these studies. Blood damage indices were found to increase with increased impeller speed or decreased flow rate. The hemolysis index for 50-microm tip gap was found to be less than 200-microm gap, despite increased shear rate. This is explained by a cell screening effect that prevents cells from entering the smaller gap. It is suggested that these parameters should be reflected in the hemolysis model not only for the design, but for the practical use of rotary blood pumps, and that further investigation is needed to explore other possible factors contributing to hemolysis.

Numerical Analysis of the Influence of the Tip Clearance Flows on the Unsteady Cavitating Flows in a Three-Dimensional Inducer

Abstract: To clarify the influences of the tip clearance flows on the unsteady cavitating flow, the three-dimensional unsteady cavitating flows through both the two-dimensional cascades and the three-dimensional inducer with and without tip clearance are performed numerically. The governing equations for the compressible fluid flow with the DES turbulence model are employed with the assumption of the isentropic process of liquid phase. The evolution of cavities is represented as the source/sink of vapor phase. The basic equations in the curve linear coordinate are solved by the finite difference method. As the results of the three-dimensional cavitating flows through the two-dimensional cascades, the tip clearance flows from the pressure side to the suction side of the blade produces the tip vortex cavitation, which affects the sheet cavitation on the leading edge of the next blade and enhances the blockage effect near the casing than the flows without tip clearance. On the other hand, in the case of the three-dimensional inducer, the large backflow cavitation is observed around the inlet of the inducer, where the cavities are developed on the casing by the tip clearance flows. The large pressure gradient between the non-cavitating pressure side and the cavitating suction side enhances the tip clearance flows. The calculation considering the tip clearance reproduces the developed cavitation region similar to that of experimental visualizations. Additionally, the backflow cavitation rotates with the speed slower than the rotation speed of the inducer. Then, the rotation of backflow cavitation causes the periodic fluctuation of the outlet pressure greater than that of the inlet pressure.

Gas turbine plant

Abstract: Provided is a gas turbine plant that enables active clearance control for ensuring tip clearance of first-stage turbine rotor blades required during start-up and for achieving the minimum tip clearance during load operation. In a gas turbine plant including a cooler in an air system used for cooling second-stage turbine stator blades, a first-stage segmented ring and a second-stage segmented ring that oppose tips of first-stage turbine rotor blades and second-stage turbine rotor blades are supported by the same blade ring member, and a cooling-air for the second-stage turbine stator blades forms a cooling air flow cooling the blade ring, to control thermal expansion of the blade ring and to control the clearance with respect to the tips.

Optical Probe for Monitoring Blade Tip Clearance

Abstract: The reduction of blade tip clearance in high pressure turbine (HPT) and high pressure compressor (HPC) engines, defined as the void between a blade tip and the surrounding casing, has been a subject of intense research since the inception of the gas turbine engine. A prototype sensor based on an interferometric ranging technique, was built and tested for monitoring tip clearances. The method provided measurement accuracy of better than 10 micrometers. It is robust, inherently self-calibrating, and insensitive to environmental variations. The performance of the sensor was evaluated in both room temperature and inside a tube furnace to simulate the turbine environment. The spatial resolution, clearance measurement accuracy, clearance measurement range, and sensitivity of the prototype sensor were determined. The sensor system will provide a new tool for engine manufacturers to study and optimize blade tip clearance with high accuracy without the need for repetitive and cumbersome calibration procedures.

Tip Clearance Effect On the Flow Pattern of a Radial Impulse Turbine For Wave Energy Conversion

Abstract: Turbines for wave energy conversion have a special feature to be taken into account in the study of the tip leakage flow: These turbines are self-rectifying, which work inside a cyclically bidirectional flow alternatively as an inflow/outflow turbine. The phenomena at the blade tip will be different in these two situations. Moreover, it is necessary to take into account the tip clearance of the guide vanes because it has a significant influence on the rotor performance. A previously developed numerical model has been used for this study. The geometry proposed by Setoguchi (2002, “A Performance Study of a Radial Impulse Turbine for Wave Energy Conversion ,” Journal of Power and Energy, 216, pp. 15–22) is used in the model. Three different tip clearance sizes have been simulated to compare the influence of the tip clearance size on the performance. Results show that changing the size of the tip clearance from 0% to 4% of the blade span reduces the turbine maximum efficiency by up to 8%. However, the efficiency reduction is more pronounced when the turbine works as an inflow turbine because the tip clearance effect is more important in the inner part of the rotor, since flow velocities are higher and the relative casing motion is lower. This study achieves its main aim, which is to improve knowledge about the phenomena related to the tip clearance and its influence on the performance of radial impulse turbines.

Active clearance control for a centrifugal compressor

Abstract: Apparatus and method of operating a centrifugal compressor and active control system includes a centrifugal compressor (18) with compressor blades (126) mounted on an impeller (32), an annular cavity (140) bounded in part by a shroud (130) adjacent to the blades (126), and an active control system (34) for controlling a clearance (180) between the shroud (130) and the blades (126) by controlling a cavity pressure (CP) in the cavity (140). An electronic controller (146) for controlling a control pressure valve (150) for pressurizing using a source of compressor discharge pressure air (76) and depressurizing the cavity (140) respectively may open and close the valves using pulse width modulation. Pressure and clearance sensors (160, 162) positioned for measuring the cavity pressure (CP) the blade tip clearance (180) respectively in signal supply communication with the electronic controller (146) may be used. The shroud (130) may be supported by radially spaced apart annular radially outer and inner supports (132, 134) connected to a casing (114) by a bolted joint (136) bounding the cavity (140)

Development of a Low Flow Coefficient Single Stage Centrifugal Compressor

Abstract: A low flow coefficient unshrouded centrifugal compressor would give up clearance in relation to the span of the blades, because centrifugal compressors produce a sufficiently large pressure rise in fewer stages This problem is more acute for a low flow high-pressure ratio impeller The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin Thus a design of a high efficiency and wide operation range for a low flow coefficient centrifugal compressor is a great challenge This paper describes a new development of high efficiency and large surge margin low flow coefficient (0145) centrifugal compressor A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in this centrifugal compressor design The new compressor has three main parts: impeller, a low solidity diffuser, and volute The tip clearance is under special consideration in this design to allow impeller insensitivenes

Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

Abstract: This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ—f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage ...

Experimental Research for Performance and Noise of Small Axial Fan

Abstract: Small axial fans have become widely used as cooling devices in recent years. Because of their increasing importance, studies have been conducted on ways to improve the performance and reduce the noise of such fans. In this report, a small axial fan with a diameter of 85 mm (a type popularity used in personal computer or workstation) was selected for further examination. The influence on aerodynamic performance and noise of such frame design parameters as blade tip clearance results in a decrease of discrete frequency noise and an increase of broad-spectrum noise. As for the most suitable design refinement in terms of fan efficiency, we found that the treatment of outlet corner roundness and altering spoke skew to the direction counter to that of fan rotation was effective.

Cavitation and flow instabilities in a 3-bladed axial inducer designed by means of a reduced order analytical model

Abstract: The present paper illustrates the main results of an experimental campaign conducted using the CPRTF (Cavitating Pump Rotordynamic Test Facility) at Alta S.p.A. The tests were carried out on the DAPAMITO inducer, a three-bladed axial pump designed and manufactured by Alta S.p.A. using a simplified analytical model for the prediction of geometry and noncavitating performance of typical space rocket inducers. The transparent inlet section of the facility was instrumented with several piezoelectric pressure transducers located at three axial stations: inducer inlet, outlet and the middle of the axial chord of the blades. At each axial station at least two transducers were mounted with given angular spacing in order to cross-correlate their signals for amplitude, phase and coherence analysis. However, probably because of the high value of the blade tip clearance, very few flow instabilities have been detected on the inducer, including: steady asymmetric cavitation caused by the different extension of the cavitating regions on the blades; cavitation surge at a frequency equal to 0.16 times the inducer rotational frequency; a higher-order axial phenomenon at 7.2 times the rotational frequency.

Study of Sweep and Induced Dihedral Effects in Subsonic Axial Flow Compressor Passages—Part I: Design Considerations—Changes in Incidence, Deflection, and Streamline Curvature

Abstract: This article presents the study of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low-speed axial compressor rotor blades against the performance of baseline unswept rotor (UNS) for different tip clearance levels. The first part of the paper discusses the changes in design parameters when the blades are swept, while the second part throws light on the effect of sweep on tip leakage flow-related phenomena. 15 domains are studied with 5 sweep configurations (0∘, 20∘ TCS, 30∘ TCS, 20∘ AXS, and 30∘ AXS) and for 3 tip clearances (0.0%, 0.7%, and 2.7% of the blade chord). A commercial CFD package is employed for the flow simulations and analysis. Results are well validated with experimental data. Forward sweep reduced the flow incidences. This is true all over the span with axial sweeping while little higher incidences below the mid span are observed with tip chordline sweeping. Sweeping is observed to lessen the flow turning. AXS rotors demonstrated more efficient energy transfer among the rotors. Tip chordline sweep deflected the flow towards the hub while effective positive dihedral induced with axial sweeping resulted in outward deflection of flow streamlines. These deflections are more at lower mass flow rates.

Time Resolved Experimental Investigations of an Axial Compressor With Casing Treatment

Abstract: A casing treatment with axial and radial skewed slots ending in a plenum chamber has experimentally been investigated at a highly subsonic axial compressor stage. The aim was to investigate the physical phenomenon of this treatment family that is responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. The experimentally gained performance results of this configuration showed an extension of the operating range by approximately 50%, while the efficiency for design conditions is reduced by 1.4%. Apart from this, operating points at part load conditions have been observed nearly without any loss in efficiency. The detailed flow analysis is performed by means of results from a 3D pneumatic probe with temperature sensor and a dynamic total pressure probe. The focus of the investigations is on the incidence flow to the compressor rotor, the tip clearance vortex flow in combination with the wall stall separation region and the blade stall due to suction side separation. The casing treatment configuration is investigated with a special interest in detecting those effects which have an impact on the stability and the compressor overall efficiency, including the interaction of the rotor and the stator flow fields.

Effects of thermal boundary condition, fin size, spacing, tip clearance, and material on pressure drop, heat transfer, and entropy generation optimization for forced convection from a variable-height shrouded fin array

Abstract: Fully developed forced convection through a variable-height shrouded fin array is studied numerically. Two different base thermal boundary conditions are considered being isothermal and isoflux heating. In either case, the shroud is assumed to be adiabatic. Following the application of two separate thermal energy equations, the conjugate heat transfer problem is solved. Different fin material, spacing, height, tip clearance, and size are examined. Considering these effects, pressure drop, heat transfer, and entropy generation aspect of the problem are studied in detail.

The Effect of Rotor Tip Clearance Size onto the Separated Flow Through a Super-Aggressive S-Shaped Intermediate Turbine Duct Downstream of a Transonic Turbine Stage

Abstract: The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters, which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any loss generating separation or flow disturbances. Due to costs and weight this intermediate turbine duct (ITD) has to be as short as possible. This leads to an aggressive (high diffusion) and further to a super-aggressive s-shaped duct geometry. In order to investigate the influence of the blade tip gap size on such a high diffusion duct flow a detailed test arrangement under engine representative conditions is necessary. Therefore, the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology has been adapted: An super-aggressive intermediate duct is arranged downstream of a transonic HP-turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees. A second LP-vane row is located at the end of the duct and represents the counter rotating low pressure turbine at a larger diameter. A following deswirler and a diffuser are the connection to the exhaust casing of the facility. In order to determine the influence of the blade tip gap size on the flow through such a super-aggressive s-shaped turbine duct measurements were conducted with two different tip gap sizes, 1.5% span (0.8 mm) and 2.4% span (1.3 mm). The aerodynamic design of the HP-turbine stage, ITD, LP-vane and the de-swirler was done by MTU Aero engines. In 2007 at ASME Turbo Expo the influence of the rotor clearance size onto the flow through an aggressive ITD was presented. For the present investigation this aggressive duct has been further shortened by 20% (super-aggressive ITD) that the flow at the outer duct wall is fully separated. This paper shows the influence of the rotor tip clearance size onto this separation. The flow through this intermediate turbine duct was investigated by means of five-hole-probes, static pressure taps, boundary layer rakes and oil flow visualisation. The oil flow visualisation showed the existence of vortical structures within the separation where they seem to be imposed by the upstream HP-vanes. This work is part of the EU-project AIDA (Aggressive Intermediate Duct Aerodynamics, Contract: AST3-CT-2003-502836).Copyright © 2009 by ASME

Combined Effects of Forward Sweep and Tip Clearance on the Performance of Axial Flow Compressor Stage

Abstract: There are a number of performance indices for a turbomachine on the basis of which its strength is evaluated. In the case of axial compressors, pressure ratio, efficiency and stall margin are few such indices which are of major concern in the design phase as well as in the evaluation of performance of the machine. In the process of improving the blade design, 3D blade stacking, where the aerofoil sections constituting the blade are moved in relation to the flow. Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial compressor due to modifications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the performance of a turbomachine. The present work investigates the combined effect of these two factors on various flow characteristics in a low speed axial flow compressor. The objective of the present paper is thereby confined to study the collective effects of sweep and tip clearance without attempting to suggest an outright new design. In the present numerical work, the performance of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low speed axial compressor rotor blades are studied. For this, 15 computational domains were modeled for five rotor sweep configurations and three different clearance levels for each rotor. Through the results, 20°AXS rotor is found to be distinctive among all the rotors with highest pressure rise, higher operating range and less tip clearance loss characteristics. TCS rotors produced improved total pressure rise at the low flow coefficients when the tip gap is increased. Hence there is a chance that an “optimum” tip gap exists for the TCS rotors in terms of total pressure coefficient and operating range, while AXS rotors are at their best with the minimum possible clearance.Copyright © 2009 by ASME

Model validation for an AMB-based compressor surge control test rig

Abstract: In this paper, we present experimental test data for validation of a recently introduced mathematical model for compression systems, including the dynamic effects of varying the impeller axial tip clearance. For the centrifugal compressor test rig that was built to study the suppression of surge by using active magnetic bearings (AMBs) to control its impeller tip clearance, the steady state and the dynamic response of the compression system induced by varying the impeller tip clearance are measured and compared to theoretical predictions, and the states of the compression system in surge condition are collected and analyzed. Parameters in the compression system model, such as the Greitzer parameter B and Helmholtz frequency ωн are experimentally identified. Also, the servo dynamics of the magnetic bearing that controls the axial impeller position is determined experimentally.

Numerical Investigation Into Non-Synchronous Vibrations of Axial Flow Compressors by the Resonant Tip Clearance Flow

Abstract: This work investigates Non-Synchronous Vibrations (NSV) encountered in a turbine engine axial flow compressor using a Computational Fluid Dynamics (CFD) approach. It has been proposed that the resonance of the tip clearance flow in compressor blades could be the physical mechanism behind NSV. This work’s emphasis is on being able to computationally capture this resonance and predict the critical NSV speed using CFD. This would considerably reduce the costs involved in future hardware design and testing. The model uses the same compressor blade geometry on which experimental validation of the proposed NSV theory was conducted. The flow interaction with blade vibratory motion is modeled using a moving mesh capability and a SAS-SST turbulence model is used for computation. A review of the proposed theory on NSV is done. The CFD model is first verified with experimental data and then characterized to ensure that the simulations are conducted at the proper NSV conditions, in order to assess the resonance of the tip clearance flow. Evidence of this resonance behavior is presented and critical NSV speeds are identified based on numerical results for two different inlet temperature cases and are validated against experimental data. Further study of the actual flow structure associated with NSV is done. Additional remarks on the numerical results are discussed. An iterative design methodology to account for NSV is also proposed based on the current numerical study.© 2009 ASME

Aerodynamic Performance of Low Speed Axial Flow Compressor Rotors with Sweep and Tip Clearance

Abstract: Blade tip gap, though finite, has great influence on the performance of a turbomachine. Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial...

Stall characteristics and tip clearance effects in forward swept axial compressor rotors

Abstract: Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial compressor due to modifications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the performance of a turbomachine. The present paper investigates the combined effect of these two factors on various flow characteristics in a low speed axial flow compressor. For this present study, nine computational domains were modeled; three rotor sweep configurations (0°, 20° and 30°) and for three different clearance levels for each rotor. Commercial CFD solver ANSYS CFX 11.0 is used for the simulations. Results indicated that tip chordline sweep is found to improve the stall margin of the compressor by modifying the suction surface boundary layer migration phenomenon. Diffusion Factor (DF) contours showed the severity of stalling with unswept rotor. For the swept rotors, the zones of high probable stall are less severe and they become less in size with increasing sweep. Increment in the tip gap is found to gradually affect the performance of unswept rotor, while the effect is very high for the two swept rotors for the earlier increments. As a minimum clearance is unavoidable, swept rotors suffer relatively higher deviation from the idealistic behavior than the unswept rotor due to tip clearance.

Active Rotor Alignment Control System And Method

Abstract: A rotating machine, such as a gas turbine, includes an active rotor alignment clearance control system wherein a plurality of actuators are circumferentially spaced around at least one rotor shaft bearing. The actuators are configured to eccentrically displace the bearing, and thus the rotor shaft, relative to stationary outer casing structure. A plurality of sensors are circumferentially spaced around a component of the casing structure, such as an inner shroud, and measure a parameter indicative of an eccentricity, such as blade tip clearance between the rotor blades and the structure, as the rotor rotates within the structure. A control system in communication with the sensors and actuators is configured to control the actuators to eccentrically displace the rotor by moving the shaft bearing to compensate for eccentricities detected between the rotor and casing structure.

Vane segment tip clearance control

Abstract: A compressor stator vane and rotor blade tip clearance control assembly in which a plurality of stator vane segments each with vanes extending inward are connected to an annular sync ring through eccentric cranks so that circumferential movement of the sync ring will produce radial displacement of the vane segments and control the clearance between the blade tips. An actuator piston is rigidly fixed to the sync ring and forms an actuator chamber with stationary actuator housing. Bleed off pressure from one of the compressor stages is used to move the actuator piston, which moves the sync ring to radially displace the vane segments.

Multistage Compressor and Turbine Modeling for the Prediction of the Maximum Turbine Speed Resulting From Shaft Breakage

Abstract: A mathematical model for the prediction of the maximum speed of a high pressure turbine following a shaft failure event was developed. The model predicts the high pressure compressor and ducting system pre- and post-stall behavior like rotating stall and surge after the shaft breakage. The corresponding time-dependent high pressure turbine inlet conditions are used to calculate the turbine maximum speed, taking into account friction and blade&vane tip clearance variations as a result of the rearward movement of the turbine and destruction of the turbine blading. The compressor and ducting system is modeled by a 1-dimensional, stage-by-stage approach. The approach uses a finite-difference numerical technique to solve the nonlinear system of equations for continuity, momentum and energy including source terms for the compressible flow through inlet ducting, compressor and combustor. The compressor blade forces and shaft work are provided by a set of quasi steady state stage characteristics being valid for pre-stall and post-stall operations. The maximum turbine speed is calculated from a thermodynamic turbine stand-alone model, derived from a performance synthesis program. Friction and blade&vane tip clearance variations are determined iteratively from graphical data depending on the axial rearward movement of the turbine. The compressor and ducting system model was validated in pre-stall and post-stall operation mode with measured high pressure compressor data of a modern 2-shaft engine. The turbine model was validated with measured intermediate pressure shaft failure data of a 3-shaft engine. The shaft failure model was applied on a modern 2-shaft engine. The model was used to carry out a sensitivity study to demonstrate the impact of control system reactions on the resulting maximum high pressure turbine speed following a shaft failure event.Copyright © 2009 by Rolls-Royce Deutschland Ltd. & Co. KG

Influence of Tip Clearance on Performance of a Contra-Rotating Fan

Abstract: Influences of tip clearance on the tip flow and associated loss mechanism in a contra-rotating axial flow fan has been studied in the paper, based on three dimensional numerical results. The results with different tip clearance are compared in terms of stage efficiency, relative total pressure loss coefficient, flow angle. It is found that the efficiency of the contra-rotating fan changes almost linearly with increment of the tip clearance, however, efficiency of the rear rotor is observed to decrease more dramatically than that of the forward rotor given same tip clearance variation. The analysis on the flow structure indicates that the tip region flow field is qualitatively similar in both rotors. However, with the same clearance value, the leakage flow in the rear rotor is effected by a tip leakage vortex of greater intensity caused by relative loading levels and the inter rotor interaction.