Showing papers on "Tip clearance published in 2002"

Effects of Tip Geometry and Tip Clearance on the Mass/Heat Transfer From a Large-Scale Gas Turbine Blade

Abstract: An experimental investigation has been performed to measure average and local mass transfer coefficients on the tip of a gas turbine blade using the naphthalene sublimation technique. The heat/mass transfer analogy can be applied to obtain heat transfer coefficients from the measured mass transfer data. Flow visualization on the tip surface is provided using an oil dot technique. Two different tip geometries are considered: a squealer tip and a winglet-squealer tip having a winglet on the pressure side and a squealer on the suction side of the blade. Measurements have been taken at tip clearance levels ranging from 0.6% to 3.6% of actual chord. The exit Reynolds number based on actual chord is approximately 7.2 × 105 for all measurements. Flow visualization shows impingement and recirculation regions on the blade tip surface, providing an interpretation of the mass transfer distributions and offering insight into the fluid dynamics within the gap. For both tip geometries the tip clearance level has a significant effect on the mass transfer distribution. The squealer tip has a higher average mass transfer that sensibly decreases with gap level, whereas a more limited variation with gap level is observed for the average mass transfer from the winglet-squealer tip.

Steady and Unsteady Flow Field Measurements Within a NASA 22-Inch Fan Model

Abstract: Results are presented of an experiment conducted to investigate possible sources of fan noise in the flow developed by a 22-in. (55.9 cm) diameter turbofan model. Flow diagnostic data were acquired to identify possible sources of both tone and broadband noise. Laser Doppler velocimetry was used to characterize the tip flows that develop within the rotor blade passages, the wake flow downstream of the rotor, and the shock waves that develop on the blades when operated at transonic relative tip speeds. Single-point hot-wire measurements were made in the rotor wake to determine the frequency content and the length scales of the flow unsteadiness. The results document the changes in the rotor wake flow with both rotor speed and axial distance downstream of the rotor. The data also show the tip flow development within the blade passage, its migration downstream, and (at high rotor speeds) its merging with the blade wake of the following blade. Data also depict the variation of the tip flow with tip clearance. LDV data obtained within the blade passages at high rotor speeds illustrate the passage-to-passage variation of the mean shock position. Spectra computed from the single-point hot-wire measurements illustrate how the energy in the flow oscillations is split between periodic and random components, and how this split varies with both radial and axial position in the rotor wake.

Turbine Engine Clearance Control Systems: Current Practices and Future Directions

Abstract: Improved blade tip sealing in the high pressure compressor (HPC) and high pressure turbine (HPT) can provide dramatic reductions in specific fuel consumption (SFC), time-on-wing, compressor stall margin, and engine efficiency as well as increased payload and mission range capabilities. Maintenance costs to overhaul large commercial gas turbine engines can easily exceed $1M. Engine removal from service is primarily due to spent exhaust gas temperature (EGT) margin caused mainly by the deterioration of HPT components. Increased blade tip clearance is a major factor in hot section component degradation. As engine designs continue to push the performance envelope with fewer parts and the market drives manufacturers to increase service life, the need for advanced sealing continues to grow. A review of aero gas turbine engine HPT performance degradation and the mechanisms that promote these losses are discussed. Benefits to the HPT due to improved clearance management are identified. Past and present sealing technologies are presented along with specifications for next generation engine clearance control systems.

Micro gas turbine engine with active tip clearance control

Abstract: In a micro gas turbine engine, a capacitive sensor is used for measuring a tip clearance of a radial compressor section thereof, and an actuator is used for axially displacing a rotor shaft in response to an output from the capacitive sensor. Because the capacitive change gives an accurate measure of the size of the tip clearance, a particularly high sensitivity can be achieved in parts where the tip clearance is small, thereby providing a highly precise tip clearance control.

Fan Noise Source Diagnostic Test: LDV Measured Flow Field Results

Abstract: Results are presented of an experiment conducted to investigate potential sources of noise in the flow developed by two 22-in. diameter turbofan models. The R4 and M5 rotors that were tested were designed to operate at nominal take-off speeds of 12,657 and 14,064 RPMC, respectively. Both fans were tested with a common set of swept stators installed downstream of the rotors. Detailed measurements of the flows generated by the two were made using a laser Doppler velocimeter system. The wake flows generated by the two rotors are illustrated through a series of contour plots. These show that the two wake flows are quite different, especially in the tip region. These data are used to explain some of the differences in the rotor/stator interaction noise generated by the two fan stages. In addition to these wake data, measurements were also made in the R4 rotor blade passages. These results illustrate the tip flow development within the blade passages, its migration downstream, and (at high rotor speeds) its merging with the blade wake of the adjacent (following) blade. Data also depict the variation of this tip flow with tip clearance. Data obtained within the rotor blade passages at high rotational speeds illustrate the variation of the mean shock position across the different blade passages.

Micro Air Injection and Its Unsteady Response in a Low-Speed Axial Compressor

Abstract: A new approach, steady micro air injection from the casing, is proposed to improve the stability of a three-stage low-speed axial compression system. Although the injection rate is designated to be only a few ten thousandth of the compressor flow rate, such an injection is able to trigger the unsteady response and thus lower the mass flow rate at stall for up to 5.83%. At the same time, it keeps the steady compressor characteristic with no injection unchanged. In order to verify that the compressor response is indeed unsteady, experiments at various injection configurations are performed, which include different injection angles, axial gaps between injector and blade leading edge, radial penetration of injector and the amount of injected air. Evidences of the unsteady response are further demonstrated through dynamic signal analysis using a wavelet-based method to show the behavior of early flow disturbances under the influence of injection. Numerical analyses performed at near stall condition show that the tip clearance vortices do response to the micro-injection, and thus delay the inception of stall.

Novel Approach for Reducing Rotor Tip-Clearance-Induced Noise in Turbofan Engines

Abstract: Rotor tip-clearance induced noise, in the form of both rotor self-noise and rotor-stator interaction noise, constitutes an important component of total fan noise. Innovative yet cost-effective techniques to suppress rotor-generated noise are, therefore, of foremost importance for improving the noise signature of turbofan engines. To that end, the feasibility of a passive porous treatment strategy to modify positively the tip-clearance flowfield is addressed. Accurate viscous flow calculations of the baseline and the treated rotor flowfields are studied. Detailed comparison between the computed baseline solution and experimental measurements shows excellent agreement. Tip-vortex structure, trajectory, strength, and other relevant aerodynamic quantities are extracted from the computed database. Extensive comparison between the untreated and treated tip-clearance flowfields is performed. The effectiveness of the porous treatment for altering the rotor-tip vortex flowfield, in general, and reducing the intensity of the tip vortex, in particular, is demonstrated. In addition, the simulated flowfield for the treated tip clearly shows that substantial reduction in the intensity of both the shear layer rollup and boundary-layer separation on the wall is achieved.

Ground effect wing having a variable sweep winglet

Abstract: A variable sweep winglet with a negative dihedral angle is provided for a ground effect vehicle. The winglet is positionable at a sweep angle to control the winglet tip clearance from ground. Variable winglet tip clearance reduces the risk of damage or instability due to collision with the ground or water, thereby permitting more efficient flight at lower altitude with an equivalent safety. The winglet is generally positioned by an actuator. The actuator is controlled by a flight control system, or by other manual or automatic systems. A sensor may also be included for determining whether an object lies in the path of the winglet. The sensor communicates with the flight control system in order to vary the sweep of the winglet to increase clearance from the ground or water, thus avoiding impact with the object.

Method and apparatus for measuring turbine blade tip clearance

Abstract: A method of determining blade tip clearance in a gas turbine includes (a) measuring the distance A between an ultrasonic sensor (16) and a stator shroud surface (14), (b) measuring the distance between B a radio frequency sensor (20) and rotating blade tips (13) of the gas turbine; and (c) subtracting the distance measured by the ultrasonic sensor (16) from the distance measured by the radio frequency sensor (20). The apparatus includes an ultrasonic sensor for measuring the distance between a stator shroud surface (14) and the ultrasonic sensor (16), a radio frequency sensor (20) for measuring the distance between rotating blade tips (13) of the gas turbine and the radio frequency sensor; and a computer system (24) for receiving and subtracting the ultrasonic sensor measurements from the radio frequency sensor measurements.

Wall-Normal-Free Reynolds-Stress Model for Rotating Flows Applied to Turbomachinery

Abstract: A recently developed near-wall wall-normal-free Reynolds stress model is extended and applied to the computation of transonic three-dimensional e ows in turbomachinery rotors with tip clearance. The Reynolds stress model used is completely independent of the distance-from-the-wall and of the normal-to-the-wall direction. This is achieved by using a pseudonormal direction, dee ned by the gradients of turbulence length scale and anisotropy tensor invariants, in the pressure ‐strain echo terms. The effects of rotation are included through theexact Coriolis termsin the Reynolds stress transport equations and through the isotropization of absolute e ow-production model used for the rapid pressure ‐strain terms. The model is initially validated by comparison with measurements in rotating fully developed plane channel e ows. Computational results obtained with the proposed Reynolds stress model are compared with measurements and with k‐" computations for various operating points of the NASA 37 rotor, using a 3 ££ 10 6 multiblock computational grid with 41 radial stations within the tip-clearance gap. The proposed model substantially improves the agreement with measurements compared to existing algebraic and two-equation models.

Tip Leakage Vortex Cavitation from the Tip Clearance of a Single Hydrofoil

Abstract: Focusing on the tip leakage vortex cavitation, experimental and numerical studies were carried out as the first step of the investigation of cavitations in tip leakage flow. For a single hydrofoil with a tip clearance, tip leakage vortex cavitations were observed for various cavitation numbers and angles of attack. To simulate the tip leakage vortex cavitation, a simple calculation of 2-D unsteady flow based on the slender body approximation with taking into account the effects of cavity growth (Watanabe et al., 2001) was made. The results of calculations show qualitative agreement with the experimental results with respect to the location and size of the cavity. The influences of the cavitation number, angle of attack, blade loading, and the size of tip clearance were simulated reasonably well.

Numerical Study of the Internal Flow Field Characteristics in Mixed Flow Turbines

Abstract: Presented is a numerical investigation of the characteristics of the internal flow field of a high-speed low-pressure ratio mixed flow turbine of 95.14 mm tip diameter. A commercial computational fluid dynamics (CFD) code has been successfully employed. This has been carefully validated to experimental data taken from a turbine test facility at this institution. A comparison to gated (in phase with the turbine rotation) Laser Doppler Velocimetry measurements at the turbine trailing edge and total to static efficiencies at various operating conditions, was made showing good agreement. Details of the internal flow field from a numerical study using a 393,872 cell density model are presented. These details have been compared to a radial turbine of similar geometry and performance characteristics, also analyzed using the same cell density and analysis and boundary conditions. The flow field was found to be highly three-dimensional with the tip leakage vortex as the dominant secondary flow feature. The tip clearance flow was found to be significantly influenced by the relative motion of the shroud wall, which suppressed the development of a vortex within the mainstream passage particularly in the inducer region. Comparison to the radial turbine has shown noticeable differences concentrated in the inducer region where the greater Coriolis acceleration in the radial turbine is more influential in the development of secondary flows. Considerable loss is observed localized at the blade leading edge tip region along the full length of the blade pitch; this is associated with the increased streamline curvature in the meridional plane.Copyright © 2002 by ASME

Monitoring blade passage in turbomachinery through the engine case (no holes)

Abstract: It is possible to detect passage of turbomachinery blades without penetrating the engine case. This "look through the wall" eddy current sensor eases the addition of a PHM system to an engine. This paper introduces this sensing concept, summarizes the physics, and presents results of preliminary tests. Blade material and geometry, case material, thickness and temperature, blade tip clearance, sensor detail and design and blade tip velocity all affect the strength and quality of the signal detected.

Tip Clearance Vortex Development and Shock-Vortex-Interaction in a Transonic Axial Compressor Rotor

Abstract: A great potential regarding powerful loss reduction in transonic axial flow compressors is located at the tips of the blades. In this region, losses are intensified by tip-vortices standing above the suction sides of the blades. Each vortex propagates through the blade duct in question and must cross the passage shock which is caused by the flow deflection of the neighboring blade. The shock-vortex-interaction leads to a sudden and strong deceleration of the flow and, as consequence, to a strong change in the vorticity distribution of the vortex. Depending on the intensity of the shock-vortex-interaction, vortex breakdown can occur inducing compressor surge. In order to clarify these phenomena it is necessary to analyze the flow field in the tip region. For that purpose, numerical flow simulations for a transonic axial compressor are conducted using an existing flow solver. Detailed analyses are performed concerning tip-vortex development and topology as well as shock-vortex- interaction.

Local Mass/Heat Transfer on Turbine Blade Near-Tip Surfaces

Abstract: Local mass transfer measurements on a simulated high pressure turbine blade are conducted in a linear cascade with tip clearance, using a naphthalene sublimation technique. The effects of tip clearance (0.86%–6.90% of chord), are investigated at an exit Reynolds number of 5.8 × 105 and a low turbulence intensity of 0.2%. The effects of the exit Reynolds number (4–7 × 105 ) and the turbulence intensity (0.2% and 12.0%) are also measured for the smallest tip clearance. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10% of the blade height from the tip at smaller tip clearances. At the largest tip clearance high mass transfer rates are induced at 15% of curvilinear distance (Sp /C) by the strong acceleration of the fluid on the pressure side into the clearance. The effect of tip clearance on the mass transfer is not very evident on the suction surface for curvilinear distance of Ss /C < 0.21. However, much higher mass transfer rates are caused downstream of Ss /C ≈ 0.50 by the tip leakage vortex atthe smallest tip clearance, while at the largest tip clearance, the average mass transfer is lower than that with zero tip clearance, probably because the strong leakage vortex pushes the passage vortex away from the suction surface. A high mainstream turbulence level (12.0%) increases the local mass transfer rates on the pressure surface, while a higher mainstream Reynolds number generates higher local mass transfer rates on both near-tip surfaces.Copyright © 2002 by ASME

Gas turbine engine system

Abstract: Tip clearance apparatus for a gas turbine engine comprises a shroud ring having curved portions so as to allow eccentric offset and hence asymmetric movement of the shroud. The shroud ring is mounted within a guide also having corresponding curved portions and movement of the shroud ring is controlled by the use of sensors.

Study of Rotor Tip-Clearance Flow Using Large-Eddy Simulation

Abstract: A large-eddy simulation has been performed to study the temporal and spatial dynamics of a rotor tip-clearance flow, with the objective of determining the underlying mechanisms for low pressure fluctuations downstream of the tip-gap. Simulation results are compared with experimental measurements, and favorable agreements are observed in both qualitative and quantitative sense. Typical vortical structures such as the tip-leakage vortex and tip-separation vortices are revealed, and their evolution is shown to be strongly influenced by the moving endwall and the blade wake. These vortical structures are the main sources of turbulence energy and Reynolds stresses as well as low-pressure fluctuations. Cavitation-inception analysis shows a high correlation between cavitation and the tip-leakage vortex.

Sheet metal turbine or compressor static shroud

Abstract: A static shroud for ducting an axial gas flow past an array of blades rotating about an axis, made of a sheet of metal bent to form a contiguous shroud body having a substantially uniform sheet thickness and a uniform axial profile, initiating with an upstream flange flowing into a tip clearance portion and terminating in a downstream flange.

3-D Digital PIV Measurements of the Tip Clearance Flow in an Axial Compressor

Abstract: The accurate characterization and simulation of rotor tip clearance flows has received much attention in recent years due to their impact on compressor-performance and stability. At NASA Glenn the first known three dimensional Digital Particle Image Velocimetry (DPIV) measurements of the tip region of a low speed compressor rotor have been acquired to characterize the behavior of the rotor tip clearance flow. The measurements were acquired phase-locked to the rotor position so that changes in the tip clearance vortex position relative to the rotor blade can be seen. The DPIV technique allows the magnitude and relative contributions of both the asynchronous motions of a coherent structure and the temporal unsteadiness to be evaluated. Comparison of measurements taken at the peak efficiency and at near stall operating conditions characterizes the mean position of the clearance vortex and the changes in the unsteady behavior of the vortex with blade loading. Comparisons of the 3-D DPIV measurements at the compressor design point to a 3D steady N-S solution are also done to assess the fidelity of steady, single-passage simulations to model an unsteady flow field.Copyright © 2002 by ASME

Experimental Measurements of the Flow and Heat Transfer of a Square Jet Impinging on an Array of Square Pin Fins

Abstract: An experimental investigation was conducted to explore the flow behavior, pressure drop, and heat transfer due to free air jet impingement on square in-line pin fin heat sinks (PFHS) mounted on a plane horizontal surface A parametrically consistent set of aluminum heat sinks with fixed base dimension of 25 × 25 mm was used, with pin heights varying between 125 mm and 225 mm, and fin thickness between 15 mm and 25 mm A 6:1 contracting nozzle having a square outlet cross sectional area of 25 × 25 mm was used to blow air at ambient temperature on the top of the heat sinks with velocities varying from 2 to 20 m/s The ratio of the gap between the jet exit and the pin tips to the pin height, the so-called tip clearance ratio, was varied from 0 (no tip clearance) to 1 The stagnation pressure recovered at the center of the heat sink was higher for tall pins than short pins The pressure loss coefficient showed a little dependence on Re, increased with increasing pin density, and pin diameter, and decreased with increasing pin height and clearance ratio The overall base-to-ambient thermal resistance decreased with increasing Re number, pin density and pin diameter Surprisingly, the dependence of the thermal resistance on the pin height and clearance ratio was shown to be mild at low Re, and to vanish at high Re numberCopyright © 2002 by ASME

A Study On The Leakage Characteristics Of Tip Seal Mechanism In The Scroll Compressor

Abstract: The tip seal as a sealing mechanism to reduce the leakage flow rate through the axial clearance has been widely used in scroll compressors, but the leakage characteristics of tip seal is not well clarified due to the complicated leakage path. This paper discusses the analytical results for four theoretical models used to predict the leakage flow rate and the relationship between the changes of tip clearance and leakage flow rate under various pressure ratios. In the experiment, it was found that the tip clearance increased due to reduction of the tip sealing force that pressed the tip seal against the opposite plate under small pressure difference between upstream and downstream. Among the four models, the predicted result for the nozzle flow model was most similar to experimental result. The equivalent clearance corresponding to the measured leakage flow rate was obtained by using the nozzle model. Additionally, the behavior of tip seal forced in the tip seal groove by pressure difference was measured with a laser displacement sensor to clarify the leakage phenomenon. NOMENCLATURE Hg : height of wrap tip groove Ps : suction pressure Ht : height of tip seal Pup : upstream pressure Lg : width of wrap tip groove ∆P : differential pressure Lt : thickness of tip seal ri : inner diameter of circular wrap m& : leakage mass flow rate ro : outer diameter of circular wrap Pback : groove pressure under tip seal Tup : upstream temperature Pc : compression pressure δa : clearance between tip seal and glass plate Pd : discharge pressure δs : clearance between wrap tip and glass plate Pdn : downstream pressure e : pressure ratio of Pdn to Pup INTRODUCTION In order to attain the high efficiency of scroll compressors widely used for the air-conditioning and heat pump systems, it is greatly important to minimize the leakage flow through the narrow clearances due to the pressure difference between compression chambers. Especially, when the alternative refrigerant having highpressure properties such as R410A or CO2 is applied to the scroll compressors instead of R22, the compressor efficiency decreases due to the increase of the leakage flow caused by large pressure difference between the compression chambers. Up to now, many kinds of the models to predict the leakage flow through the narrow clearances of the compressors have been proposed, and the experimental approaches to validate the analytical models have been tried [1-9]. The scroll compressors having superior compression mechanism to any other compressors have two kinds of leakage flows. One is the radial leakage flow through the axial clearance between the scroll wrap tip and the base plate of opposite scroll, the other is the tangential leakage flow through the radial clearance between the flanks of orbiting and fixed scroll wraps. In order to reduce these leakages in scroll compressors, the sealing mechanisms to control the narrow clearances have been used. Especially, it is more important to control the axial clearance for the high efficiency because the sealing length of the axial clearance is several times longer than that of the radial clearance corresponding to wrap height. Among the sealing mechanisms to control the axial clearance, the tip seal, which is placed in the groove machined on the tip of scroll wraps, has been the most widely used due to the advantages of simple structure and good sealing ability. In the previous investigations for clarifying the leakage characteristics of tip seal mechanism, Inaba et al. [10] investigated the leakage losses about three leakage paths in the case of inserting the tip seal into a groove tightly or loosely, and they also developed the assembling techniques to insert the tip seal sufficiently close to the bottom surface of groove. On the other hand, Hirano et al. [11] clarified the sealing pressure forcing the tip seal against the base plate of opposite scroll by measuring the groove pressure under the tip seal along the scroll wrap length and measured the tip seal motion with eddy current sensors. Ancel et al. [12] investigated the dynamic behavior of two different types of tip seals, which are the multi-blade and the monobloc tip seals. Youn et al. [13] developed the experimental apparatus to measure the leakage flow using tip seal under the actual operating conditions. However, it is not enough to clarify the leakage characteristics of tip seal because of the complicated leakage path. In this study, the leakage characteristics of scroll compressors having tip seal as the sealing mechanism for the axial clearance is investigated theoretically and experimentally. The calculation using four kinds of analytical models for the estimation of the leakage flow rate is conducted. The experimental apparatus having a simplified circular wrap is set up to measure the leakage flow rate, the axial clearance and the differential pressure between upstream pressure and groove pressure under the tip seal with the various pressure ratio conditions at the same time. The calculated results are compared with the experimental ones. Moreover, the behavior of tip seal in the tip seal groove is measured directly with a laser displacement sensor to clarify the leakage phenomenon.

Large-eddy simulation of a rotor tip-clearance flow

Abstract: A large-eddy simulation (LES) solver which combines an immersed-boundary technique with a curvilinear structured grid has been developed to study the temporal and spatial dynamics of a rotor tip-clearance flow, with the objective of determining the underlying mechanisms for low pressure fluctuations downstream of the rotor near the endwall. Salient feature of the numerical methodology, including the mesh topology, the treatment of numerical instability for non-dissipative schemes in a highly skewed mesh, and the parallelization of the code for shared memory platforms are discussed. Qualitative agreements have been observed between present LES and experimental measurements. The simulations indicate that the interaction between the moving endwall boundary layer and blade boundary layers and tip-leakage flow creates a highly complicated flow which is dominated by distinct vortical structures including the tip-leakage and tip-separation vortices. These vortical structures are found to convect downstream, expand in size and generate intense turbulent fluctuations in the endwall region.

Effect of Upstream Unsteady Flow Conditions on Rotor Tip Leakage Flow

Abstract: A study has been conducted, using unsteady three-dimensional Reynolds-averaged Navier-Stokes simulations to determine the impact on rotor performance of the interaction between the stator wakes and rotor tip clearance flow. The key effects of the interaction are: (1) a decrease in loss and blockage associated with tip clearance flow; (2) an increase in passage static pressure rise. Performance benefit is seen in the whole operability range of interest, from near design to high loading. The benefit is modest near design and increases with loading. Significant beneficial changes occur when the phenomenon of tip clearance flow double-leakage is present. Double-leakage occurs when the tip clearance flow passes through the tip gap of the neighboring blade. Double-leakage typically takes place at high loading but can be present at design condition, as well. A benefit due to unsteady interaction is also observed in the operability range of the rotor. A new generic causal mechanism is proposed to explain the observed changes in performance. It identifies the interaction between the tip clearance flow and the pressure pulses, induced on the rotor blade pressure surface by the upstream wakes, as the cause for the observed effects. The direct effect of the interaction is a decrease in the time-average double-leakage flow through the tip clearance gap so that the stream-wise defect of the exiting tip flow is lower with respect to the main flow. A lower defect leads to a decrease in loss and blockage generation and hence an enhanced performance compared to that in the steady situation. The performance benefits increase monotonically with loading and scale linearly with upstream wake velocity defect.© 2002 ASME

A study on an axial-type 2-D turbine blade shape for reducing the blade profile loss

Abstract: Losses on the turbine consist of the mechanical loss, tip clearance loss, secondary flow loss and blade profile loss etc.,. More than 60 % of total losses on the turbine is generated by the two latter loss mechanisms. These losses are directly related with the reduction of turbine efficiency. In order to provide a new design methodology for reducing losses and increasing turbine efficiency, a two-dimensional axial-type turbine blade shape is modified by the optimization process with two-dimensional compressible flow analysis codes, which are validated by the experimental results on the VKI turbine blade. A turbine blade profile is selected at the mean radius of turbine rotor using on a heavy duty gas turbine, and optimized at the operating condition. Shape parameters, which are employed to change the blade shape, are applied as design variables in the optimization process. Aerodynamic, mechanical and geometric constraints are imposed to ensure that the optimized profile meets all engineering restrict conditions. The objective function is the pitchwise area averaged total pressure at the 30 % axial chord downstream from the trailing edge. 13 design variables are chosen for blade shape modification. A 10.8 % reduction of total pressure loss on the turbine rotor is achieved by this process, which is same as a more than 1 % total-to-total efficiency increase. The computed results are compared with those using 11 design variables, and show that optimized results depend heavily on the accuracy of blade design.

Effects of Hub-To-Tip Ratio and Tip Clearance on Hysteretic Characteristics of Wells Turbine for Wave Power Conversion

Abstract: A Wells turbine for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. The effects of hub-to-tip ratio and tip clearance on the hysteretic characteristics of the Wells turbine have also been discussed in this paper.

Capacitive blade tip clearance measurements for a micro gas turbine

Abstract: The efficiency of a gas turbine has an inverse relationship with the clearance between the rotor blades and the casing. Recent efforts in miniaturization of micro gas turbine engines have created new challenge in tip clearance measurement. This paper describes the development of a tip clearance measurement system, based on capacitive measurement for a palm-top micro gas turbine engine. The sensor uses a ratio-metric measurement principle with synchronous detector to measure the average tip clearance between the rotor blades and the casing. A surface modification of the nonconductive compressor is used to create an electrode opposing the casing. A measurement range of 100 /spl mu/m was achieved with a resolution of 0.8 /spl mu/m.

Turbine airfoil tip

Abstract: Optimized tip performance for turbine airfoils (10) is obtained through a sequenced manufacturing process. The turbine airfoils (10) are assembled into the dovetail slots (22) of a turbine disk (20). The tips (12) of the turbine airfoils (10) assembled in the turbine disk (20) are then measured to determine the turbine airfoils (10) that do not have adequate tip clearance. The tips (12) of those turbine airfoils (10) that do not have adequate tip clearance are then machined to obtain adequate tip clearance. Once all the turbine airfoils (10) have adequate tip clearance, environmental coatings and/or thermal barrier coatings are applied to the blade tips (12).

Active flow control to improve the aerodynamic and acoustic performance of axial turbomachines

Abstract: The tip clearance flow of axial turbomachines is important for their aerodynamic a nd acoustic performance. The rotating instability phenomena and the tip clearance noise are observed on axial turbomachines with significant tip clearance. Previous investigations show that it is possible to reduce the tip clearance noise and improve the aerodynamic performance of the fan by mounting a turbulence generator into the tip clearance gap. In this paper it is shown that these improvements can be obtained without any modification of the tip clearance gap itself by actively controlling the tip clearance flow. To achieve this, air is injected into the gap through slit nozzles mounted flush with the inner casing wall. With steady air injection it is possible to obtain ‐ with a small injected mass flow ‐ a remarkable reduction of the noise level along with an improved aerodynamic performance. With larger injected mass flows, significant improvements of the ae rodynamic performance a re obtained at t he expense of a steep increase of the noise level. Unsteady air injection synchronized with the impeller rotation yields a significant improvement of the aerodynamic performance acc ompanied by a substantial i ncrease of the noise level. Rotating instability and tip clearance noise c an be reduced in both cases. Flow investigations with a simplified stationary 2D blade cascade show that steady air injection leads to a diminished b lade tip vortex and with it t o an improved aerodynamic performance.