Showing papers on "Tip clearance published in 2007"

Large-eddy simulation analysis of mechanisms for viscous losses in a turbomachinery tip-clearance flow

Abstract: The tip-leakage flow in a turbomachinery cascade is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the vicinity of the tip gap. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving endwall. Gross features of the tip-leakage vortex, tip-separation vortices, and blade wake have been revealed by investigating their revolutionary trajectories and mean velocity fields. The tip-leakage vortex is identified by regions of significant streamwise velocity deficit and high streamwise and pitchwise vorticity magnitudes. The tip-leakage vortex and the tip-leakage jet which is generated by the pressure difference between the pressure and suction sides of the blade tip are found to produce significant mean velocity gradients along the spanwise direction, leading to the production of vorticity and turbulent kinetic energy. The velocity gradients are the major causes for viscous losses in the cascade endwall region. The present analysis suggests that the endwall viscous losses can be alleviated by changing the direction of the tip-leakage flow such that the associated spanwise derivatives of the mean streamwise and pitchwise velocity components are reduced.

Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part I: Effect of Tip Geometry and Tip Clearance Gap

Abstract: A numerical study has been performed to investigate the effect of tip geometry on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. Baseline flat tip geometry and squealer type geometries namely double squealer or cavity and suction side squealer were considered. The performances of the squealer geometries, in terms of the leakage mass flow and heat transfer to the tip, were compared with the flat tip at two different tip clearance gaps. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modelled using three different models namely standard k-e, low Re k-ω and SST k-ω, in order to assess the capability of the models in correctly predicting the blade heat transfer. The heat transfer and static pressure distributions obtained using the SST k-ω model was found to be in close agreement with the experimental data. It was observed that compared to the other two geometries considered, the cavity tip is advantageous both from the aerodynamic and from the heat transfer perspectives by providing a decrease in the amount of leakage, and hence losses, and average heat transfer to the tip. In general, for a given geometry, the leakage mass flow and the heat transfer to the tip increased with increase in tip clearance gap. Part II of this paper examines the effect of relative casing motion on the flow and heat transfer characteristics of tip leakage flow. In Part III of this paper the effect of coolant injection on the flow and heat transfer characteristics of tip leakage flow is presented.Copyright © 2007 by ASME

The Behavior of Tip Clearance Flow at Near-Stall Condition in a Transonic Axial Compressor Rotor

Abstract: It is known that the tip clearance flow is dominant and very important flow phenomena in axial compressor aerodynamics because the tip clearance flow has a great influence on the stability as well as aerodynamic loss of compressors. Our goal is to clarify the behavior of tip clearance flow at near-stall condition in a transonic axial compressor rotor (NASA Rotor 37). In the present work, steady and unsteady RANS simulations were performed to investigate vortical flow structures and separated flow field near the tip for several different clearance cases. Boundary layer separation on the casing wall and blade suction surface was investigated in detail for near-stall and stall condition. In order to understand such complicated flow field, vortex cores were identified using the critical point theory and a topology of the three-dimensional separated and vortical flows was analyzed. In the nominal clearance case, the breakdown of tip leakage vortex has occurred at a near-stall operating condition because of the interaction of the vortex with the shock wave, leading to a large blockage and unsteadiness in the rotor tip. On the other hand, the calculation with no clearance suggested that the separation on the suction surface was different from that with the nominal clearance. Since the shock wave induced the boundary layer separation on the blade suction surface in the transonic axial compressor rotor, focal-type critical points appeared on the suction surface near the tip at near-stall condition.Copyright © 2007 by ASME

Vortex Dynamics and Low-Pressure Fluctuations in the Tip-Clearance Flow

Abstract: The tip-clearance flow in axial turbomachines is studied using large-eddy simulation with particular emphasis on understanding the unsteady characteristics of the tip-leakage vortical structures and the underlying mechanisms for cavitation-induring low-pressure fluctuations. A systematic and detailed analysis of the velocity and pressure fields has been made in a linear cascade with a moving end-wall. The generation and evolution of the tip-leakage vortical structures have been investigated throughout the cascade using mean streamlines and λ 2 contours. An analysis of the energy spectra and space-time correlations of the velocity fluctuations suggests that the tip-leakage vortex is subject to a pitchwise low frequency wandering motion. Detailed statistics of the pressure fields has been analyzed to draw inferences on cavitation

Periodical Unsteady Flow Within a Rotor Blade Row of an Axial Compressor—Part II: Wake-Tip Clearance Vortex Interaction

Abstract: In this two-part paper results of the periodical unsteady flow field within the third rotor blade row of the four-stage Dresden Low-Speed Research Compressor are presented. The main part of the experimental investigations was performed using Laser-Doppler-Anemometry. Results of the flow field at several spanwise positions between midspan and rotor blade tip will be discussed. In addition time-resolving pressure sensors at midspan of the rotor blades provide information about the unsteady profile pressure distribution. In part II of the paper the flow field in the rotor blade tip region will be discussed. The experimental results reveal a strong periodical interaction of the incoming stator wakes and the rotor blade tip clearance vortices. Consequently, in the rotor frame of reference the tip clearance vortices are periodical with the stator blade passing frequency. Due to the wakes the tip clearance vortices are separated into different segments. Along the mean vortex trajectory these parts can be characterised by alternating patches of higher and lower velocity and flow turning or subsequent counterrotating vortex pairs. These flow patterns move downstream along the tip clearance vortex path in time. As a result of the wake influence the orientation and extension of the tip clearance vortices as well as the flow blockage periodically vary in time.Copyright © 2007 by ASME

Plasma blade tip clearance control

Abstract: A gas turbine engine plasma blade tip clearance control system (11) includes an annular shroud (72) surrounding rotatable blade tips (82) and an annular plasma generator (2) spaced radially outwardly and apart from the blade tips (82). An exemplary embodiment of the annular plasma generator (2) is mounted to the annular shroud (72) and includes radially inner and outer electrodes (3, 4) separated by a dielectric material (5) disposed within an annular groove (6) in a radially inwardly facing surface (7) of the annular shroud (72). The plasma generator (2) is operable for producing an annular plasma between the annular shroud (72) and blade tips (82) and an effective clearance (ECL) produced by the annular plasma between the annular shroud (72) and blade tips (82) that is smaller than a clearance (CL) between the annular shroud (72) and blade tips (82).

Rotor thrust balance activated tip clearance control system

Abstract: A gas turbine engine with a rotor shaft that is moveable in an axial direction so change a blade tip clearance, where the rotor is displaced by a spring to increase the blade tip clearance and is displaced by a pressure created by the compressor and turbine during engine operation that will close the blade tip clearance. This is especially useful during engine shutdown to prevent blade tip rubbing against the stationary shrouds.

Reduced tip clearance losses in axial flow fans

Abstract: An axial fan assembly including a casing wall with a forward facing step formed therein and a fan rotor with blade tips, each having an aft facing step which radially overlaps the casing step so as to reduce the clearance backflow loss in the assembly. A vane is attached to the suction side of each of the blade tips with the vane having an aft facing step which radially overlaps the casing forward facing step to promote further reduction of clearance backflow. Variations on the invention include the option of an additional inlet bellmouth piece that further restricts the clearance flow and wedges integral to the casing step to improved flow stability.

Modeling of 3-D Losses and Deviations in a Throughflow Analysis Tool

Abstract: This contribution is dedicated to the modeling of the end-wall flows in a throughflow model for turbomachinery applications. The throughflow model is based on the Euler or Navier-Stokes equations solved by a Finite-Volume technique. Two approaches are presented for the end-wall modeling. The first one is based on an inviscid formulation with dedicated 3-D distributions of loss coefficient and deviation in the end-wall regions. The second approach is directly based on a viscous formulation with no-slip boundary condition along the annular end-walls and blade force modification in the region close to the end-walls. The throughflow results are compared to a series of 3-D Navier-Stokes calculations averaged in the circumferential direction. These 3-D calculations were performed on the three rotors of a low pressure axial compressor, for a series of tip clearance values.

Control of Rotating Stall in Axial Compressors Using Plasma Actuators

Abstract: This paper proposes the use of SDBD plasma actuators to suppress rotating stall inception and extend the stable operating range of axial compressors. Plasma actuators may provide a practical low-power alternative to effectively increase the surge margin of aircraft engines with minimal or even positive impact on compressor performance. A computational study is carried out on a representative subsonic modern compressor rotor geometry to evaluate the proposed casing plasma actuation for suppression of short (spike) as well as long (modal) length-scale rotating stall inception based on their respective flow physics. The objective is to assess the optimum actuator location and required actuation strength to achieve the desired effects at low and medium subsonic compressor speed. Results show that plasma actuation near the rotor leading edge and concentrated in the tip clearance gap region most effectively suppresses both of the criteria for spike stall inception and delays the predicted stall point to a lower flow coefficient with relatively low power input. In addition, the observed increase in rotor pressure rise characteristic from the proposed actuation means that the concept, with a new suggested actuator modification, can also be used to suppress modal stall inception. The simulations indicate that actuation effectiveness decreases with increasing compressor speed and that stronger actuation strength than that of conventional SDBD plasma actuators may be needed. Some implications for the practical implementation of this concept on real compressors are also discussed.

Suppression of Short Length-Scale Rotating Stall Inception With Glow Discharge Actuation

Abstract: This paper proposes and investigates the pioneering use of glow discharge (plasma) actuation to suppress short length-scale (spike) rotating stall inception. A single dielectric barrier discharge plasma actuator basically consists of two parallel offset thin electrodes separated by a dielectric material. The application of a high frequency AC voltage across the electrodes results in an induced body force on the flow adjacent to the surface. This simple, robust actuator may provide a practical low-power mean to positively alter the tip clearance flow dynamics responsible for spike stall inception. A computational study is carried out on a low-speed compressor rotor with the implementation of a published plasma actuation model in an established turbomachinery CFD code. The objective is to provide a preliminary assessment of the effectiveness of a casing circumferential plasma actuator, with varying actuator location, input voltage and frequency, in suppressing the two flow criteria associated with the formation of spike disturbances leading to stall. Results show that plasma actuation most effectively suppresses both of these flow criteria when placed near the rotor leading edge and delays the predicted stall point to a lower flow coefficient with minimal power input. The simulations also indicate that the effectiveness of the actuation decreases non-linearly with input voltage and frequency. In addition, results indicate that this technology could perhaps be used for suppression of both short and long-length scale stall inception in axial compressors.Copyright © 2007 by ASME

Tip clearance effect on high-pressure compressor stage matching:

Abstract: Tip clearance flows have a major impact on both performance and stability of high-pressure compressors (HPC). The purpose of this paper is to underline how tip clearance variations affect the matching of compressor stages, hence modifying the efficiency and stall margin of the compressor. The practical application covered by the scope of this article is a modern highly loaded HPC dedicated to civil aircraft propulsion.The first part of the paper gives a very simple overview of stagewise matching in multistage compressors. Also, this part introduces the subject of the impact of tip clearance on stage matching.The second part of the paper illustrates the effect of increased rear block clearances on performance and stability, using some available experimental data. Finally, it is shown that three-dimensional multi-stage calculations can predict the effect of tip clearance variations on stage pressure-rise characteristics and on stage matching. This validated numerical tool therefore allows the aerody...

A novel integrated rotor of axial blood flow pump designed with computational fluid dynamics.

Abstract: Due to the smaller size, smaller artificial surface, and higher efficiency, axial blood pumps have been widely applied in clinic in recent years. However, because of its high rotor speed, axial flow pump always has a high risk for hemolysis, which the red blood cells devastated by the shearing of tip clearance flow. We reported a novel design with the integrated blade-shroud structure that was expected to solve this problem by abolishing the radial clearance between blade and casing designed with the techniques of computational fluid dynamics (CFD). However, the numerical simulation result of the newly designed structure showed an unexpected backflow (where flow velocity is reverse of the main flow direction) at the blade tip. In order to eliminate this backflow, four flow passes were attempted, and the expansion angles (which reflect the radial amplification of the flow pass, on the meridional section, and should be defined as the angle between the center line of the flow pass and the axial direction) of the blades of the integrated rotor are 0 degrees, 8 degrees, 15 degrees, and 20 degrees, respectively. In the CFD result, it could be easily found as the expansion angles increased, the backflow was restrained gradually, and was eliminated at last. After numerous "cut and try" circles, the pump model was finally optimized. The numerical simulation of this model also showed a stable hydraulic characteristic.

Gas turbine with active tip clearance control

Abstract: A gas turbine engine includes a compressor, combustor, and turbine having a row of blades mounted inside a surrounding turbine shroud. A heat exchanger is used for cooling pressurized air bled from the compressor. A distribution network joins the heat exchanger to the turbine for selectively channeling air from the heat exchanger below the blades and above the shroud for controlling blade tip clearance.

Outlet guide vanes for axial flow fans

Abstract: An outlet guide vane system is disclosed for axial flow fans. Construction details are described which reduce losses in the end wall regions of the vanes, particularly for axial flow fans operating at low flow coefficient with strong localized swirl associated with upstream rotor tip clearance flows. In the preferred embodiment, the vane spanwise airfoil stacking line is approximately straight, while leaning circumferentially toward the incoming swirl flow over the majority of the radial span. The stacking line then curves abruptly in the opposite direction over the radially outboard spanwise portion, so as to lean away from the incoming swirl at the vane tip station. The radially outboard portion of the vanes simultaneously include a gradual increase in vane stagger angle, vane camber angle and vane chord. The vane may also include an axial sweep component.

Performance analysis of a transonic high-pressure turbine

Abstract: Efficiency is a crucial design parameter in any turbine development. This research presents a detailed investigation on the efficiency of a modern transonic high-pressure turbine. The work ...

Time Resolved Investigations of an Axial Compressor With Casing Treatment: Part 2 — Simulation

Abstract: A casing treatment with axial and radial skewed slots ending in a plenum chamber has numerically been investigated at a highly subsonic axial compressor stage. The aim was to understand the physical phenomena of this treatment family that are responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. Unsteady 3D Reynolds-averaged simulations were performed with the commercial CFD Code TASCflow 2.12. The closure problem was faced with a standard k-e high Reynolds turbulence model and a logarithmic wall function. Two configurations with solid casing and casing treatment were investigated at the operating points with maximum efficiency and on the stability line. The experimentally gained performance results of this configuration show an extension of the operating range of approximately 50% based on the operating range at nominal speed, while the efficiency for design conditions falls by 1.4%. Apart from this, measurements at part load conditions show operating points without any loss in efficiency. The numerical simulations predict this efficiency drop as well. The detailed analysis is performed for the solid casing and casing treatment configuration at the operating point on the stability line. Influences of the incidence flow, the tip clearance vortex and the blade suction side separation were investigated. Special interest is directed towards the interaction of the casing treatment with the blade passage flow field and a detailed analysis of the flow inside the casing treatment, the effect of the plenum chamber and the interaction with the treatment slot flow is performed.© 2007 ASME

Fabrication and high-speed characterization of SU-8 shrouded two-dimensional microimpellers

Abstract: In this study, the performance of shrouded two-dimensional microimpellers was measured for application to a micro centrifugal pump used in a portable fuel cell system. Two types of microimpellers were designed, and fabricated by a multi-layer photolithography process using an ultrathick photoresist (SU-8 3000). Microimpellers with a diameter of 10 mm were tested using an air spindle up to maximum rotation speeds determined by the destruction of the microimpellers, which are 350 000 rpm for a purely-radial-outlet blade impeller and 450 000 rpm for a backward blade impeller. The purely-radial-outlet blade impeller showed a higher pressure rise—2.8 kPa at 150 000 rpm, 5.1 kPa at 200 000 rpm and 12.5 kPa at 300 000 rpm. The measured performance satisfies the requirement of the micro centrifugal pump. However, the measured pressure rises are roughly half of the simulated values. The influence of the radial clearance and height difference between the impeller and the diffuser was investigated using an electromagnetic motor and impellers with a diameter of 16 mm. Against expectation, a better pumping performance was obtained with a larger tip clearance, and the height difference did not affect the pumping performance. These unexpected results suggest that the tip clearance and the clearance between the impeller shroud and the stationary housing act as a diffuser.

Study on flow fields in variable area nozzles for radial turbines

Abstract: The flow behind the variable area nozzle which corresponds to the flow at the leading edge of the impeller was measured with a 3-hole yaw probe and calculated with CFD. Two nozzle throat-areas were investigated. One is the smallest and the other is the largest opening for the variable nozzle. Test results agreed with the calculated results qualitatively. The leakage flow through the tip clearance of the nozzle vane significantly affected the flow field downstream of the nozzle vane with the smallest opening. However, the effect on leakage flow on the flow field downstream of the nozzle vane with the largest opening was very weak and the effect of wake is dominant. Keywords : Radial turbine, Nozzle vane, Variable geometry turbine, Clearance flow 1. Introduction In order to comply with tightening emission regulations and to reduce fuel consumption, turbochargers represent a key component for Diesel engines. Variable geometry turbines are widely used to improve engine-turbocharger matching and currently common in Diesel engines. A pivoting nozzle vane moved with an actuator is especially suited to realizing optimal turbine output for the different engine operating points. Hence, the term of variable geometry turbine usually indicates the radial turbine with a pivoting nozzle vane. Hence, this paper also calls a pivoting nozzle vane to a variable area nozzle.

Effects of Steady Tip Clearance Asymmetry and Rotor Whirl on Stall Inception in an Axial Compressor

Abstract: Effects of rotor centerline offset and whirl on the pre-stall and stall inception behavior of a high-speed tip-critical axial compressor were investigated The observations were made using a circumferential array of unsteady pressure transducers The maximum amount of rotor offset and whirl used in this investigation was 26% and 13% of the design axisymmetric tip clearance respectively Measurements were conducted using transient throttle movements which quickly decreased the mass flow in the compressor until the onset of rotating stall A second set of measurements used quasi-transient throttling starting from a mass flow about 05% larger than the stalling mass flow These data were analyzed with the traveling wave energy method, visual inspection of the filtered pressure traces, and a two-point spatial correlation technique For the uniform tip clearance case rotating stall occurred while the slope of the pressure rise characteristic was negative As expected, the flow breakdown exhibited “spike” inception with no observable rotating disturbances in the pre-stall time period The introduction of small levels of steady and unsteady tip clearance asymmetry did not significantly alter the time average performance of the stage; circumferential variations in pressure rise and flow coefficient were minimal and the stalling flow coefficient remained unchanged However, significant short length-scale rotating disturbances were observed in both of these cases prior to stall inception As in the symmetric tip clearance case, short length-scale disturbances initiated rotating stall in the non-uniform tip clearance experiments The location of the generation of the incipient stall cells with respect to the non-uniform tip clearance was strongly effected by the rotor offset/whirlCopyright © 2007 by ASME

Computational Approach for Predicting Stall Inception in Multistage Axial Compressors

Abstract: A new time-accurate computational approach for predicting stall inception due to long- and short-wavelength phenomena in multistage axial compressors is introduced. The computational approach uses a time-accurate single-blade-passage multi-blade-row strategy that includes many of the primary unsteady modes associated with the early symptoms of stall. High-frequency unsteadiness due to self-excited flow at scales of the blade passage and rotor tip clearance as well as low-frequency unsteadiness due to longitudinal system modes are included in this model. The new approach is demonstrated using the NASA Stage35 single-stage configuration with an extended up- and downstream duct. Nothing precludes the use of this model, however, for multistage and/or multipassage per blade-row configurations if the computer resources are available. The results from a series of time-accurate simulations near stall with this new approach are presented to demonstrate the self-excited unsteady pressure levels and frequencies that are computed to exist before, during, and just after stall. Results show that the self-excited flow has significant unsteady pressure amplitude and a spectrum containing both low-frequency system waves and high/moderate-frequency waves corresponding to the passage self-excited viscous flow in each blade row.

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

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

Time Resolved Investigations of an Axial Compressor With Casing Treatment: Part 1 — Experiment

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.Copyright © 2007 by ASME

Over Rotor Casing Surface Streak Measurements in a High Speed Axial Compressor

Abstract: Time averaged wall shear stress patterns were recorded during quasi-steady throttling to stall in a high speed compressor. The technique utilized a CCD camera to capture digital images of oil streaks on a transparent casing section located over the rotor. The most notable feature of the surface streaking was a bifurcation line of zero time average axial shear stress. The location of this feature was found to represent the location where the approach fluid and the reverse flow from the tip gap meet and separate from the casing surface. The location of this line with respect to the rotor leading edge was denoted as xzs . The values of xzs were found to be positive (downstream of the leading edge) at high flow coefficients, and moved upstream as the compressor mass flow was reduced. Compressor stall was observed to occur when xzs was negative, with magnitude of order 6% of the axial blade tip chord. In other words, the zero axial shear line crossed the leading edge plane at a flow coefficient slightly higher than the stall point. The present paper describes the location of xzs as a function of both the flow coefficient and the local blade tip clearance. Both of these independent variables were found to have a substantial impact on the endwall flow near the leading edge, with little variation downstream. A simplified model was used to better understand the flow mechanisms associated with changes in xzs . An interpretation of these results will be given in terms of experimental and computational efforts related to blade tip flows that are described in the recent literature.Copyright © 2007 by ASME

Axial flow turbine

Abstract: PROBLEM TO BE SOLVED: To provide an axial flow turbine with improved performance by preventing turbulence of a bypass flow flowing in a tip clearance in a moving blade.SOLUTION: The axial flow turbine includes: a moving blade 4 to be rotated around a rotational axis C in a main flow passage 2 of a casing 3; a concave cavity part 10 formed in the casing 3 at the position facing the moving blade 4; a seal fin 16 extending outward in the radial direction from the end of the moving blade 4 toward the cavity part 10; and a partition part 13 projecting from the wall surface of the cavity part 10 to a direction of reducing a distance between the cavity part 10 and the seal fin 16. The seal fin 16 is a ring plate-like member inclined toward the outside in the radial direction and also toward one end of the rotational axis C or the other end thereof. The partition part 13 is projected toward the seal fin 16 from a section which is a part of the side wall surface 11 of the cavity part 10 extending to the radial direction and faces an area where the distance between the seal fin 16 and the cavity part 10 is wide.

Blade structure of gas turbine

Abstract: To reduce secondary flow loss and to improved turbine efficiency, a section located radially outward of a border section 28 of a stationary blade 21 is bent in the rotational direction of a rotor. Thus, even if combustion gas leaks from a tip clearance between an end wall of a casing and a tip portion of a rotor blade, and a stagnation line 35 near a tip portion 22 is situated in the side of a back surface 24, because a section located radially outward of the border section 28 is bent in the rotational direction of the rotor, the stagnation line 35 is also situated toward the rotational direction of the rotor. Therefore, the stagnation lines 35 formed at various heights in the heightwise direction of the stationary blade 21 are generally aligned in the rotational direction of the rotor. Thus, fluctuation of pressure distribution in the heightwise direction of the stationary blade 21, of the combustion gas flowing into the stationary blade 21 can be reduced. As a result, secondary flow loss can be reduced and turbine efficiency can be improved.

Unsteady tip clearance flow pattern in an isolated axial compressor rotor with micro tip injection

Abstract: A numerical study of the effect of discrete micro tip injection on unsteady tip clearance flow pattern in an isolated axial compressor rotor is presented, intending to better understand the flow mechanism behind stall control measures that act on tip clearance flow. Under the influence of injection the unsteadiness of self-induced tip clearance flow could be weakened. Also the radial migration of tip clearance vortex is confined to a smaller radial extent near the rotor tip and the trajectory of tip clearance flow is pushed more downstream. So the injection is beneficial to improve compressor stability and increase static pressure rise near rotor tip region. The results of injection with different injected mass flow rates show that for the special type of injector adopted in the paper the effect of injection on tip clearance flow may be different according to the relative strength between these two streams of flow. For a fixed injected mass flow rate, reducing the injector area to increase injection velocity can improve the effect of injection on tip clearance flow and thus the compressor stability. A comparison of calculations between single blade passage and multiple blade passages validates the utility of single passage computations to investigate the tip clearance flow for the case without injection and its interaction with injected flow for the case with tip injection.