Experimental investigation about the effect of non-axisymmetric wake impact on a low speed axial compressor

Non-axisymmetric wake impact experiments were carried out after the best exciting frequency for a low speed axial compressor had been found by axisymmetric wake impact experiments. When the number and circumferential distribution of inlet guide vanes （IGV） are logical, the wakes of non-axisymmetric IGVs can exert beneficial unsteady exciting effect on their downstream rotor flow fields and improve the compressor＇s performance. In the present paper, four non-axisymmetric wake impact plans were found working better than the axisymmetric wake impact plan. Compared with the base plan, the best non-axisymmetric plan increased the compressor＇s peak efficiency, and the total pressure rise by 1.1 and 2%, and enhanced the stall margin by 4.4%. The main reason why non-axisymmetric plans worked better than the axisymmetric plan was explained as the change of the unsteady exciting signal arising from IGV wakes. Besides the high-frequency components, the nonaxisymmetric plan generated a beneficial low-frequency square-wave exciting signal and other secondary frequency components. Compared with the axisymmetric plan, multifrequency exciting wakes arising from the non-axisymmetric plans are easier to get coupling relation with complex vortices such as clearance vortices, passage vortices and shedding vortices.

Numerical study of a 3.5-stage axial compressor at on-and off-design conditions

Numerical investigation is conducted on a 3.5-stage axial compressor,on which numerous experimental projects were carried out at the Institute during the last years and an experimental database was established.In the current study five on-and off-design operating points are simulated using a RANS solver and the results are compared with the measurement.The result shows that the compressor performance can be qualitatively predicted by the mixing-plane method.Better agreement is obtained for the on-design operating point.However,as the flow unsteadiness is insufficiently considered,the numerical method produces end-wall low-speed flow layers accumulated with the flow passing through the passage,which is in no good agreement with the experimental data.In the numerical simulation the rotor rows receive less work and this difference from the measurement increases with the rotational speed.In contrast,the stator rows increase the pressure more efficiently than the measurement.In the simulation the flow in the last stator row tends more to separate on the pressure side of the blade.For the operating points close to the surge line,the predicted separation is more intense than the experimental observation.But for the operating points close to the choke,the separation is suppressed.

Structural and Conceptual Design Analysis of an Axial Compressor for a 100 MW Industrial Gas Turbine (IND100)

The structural design of the IND100 axial compressor requires a multistage interrelationship between the thermodynamic, aerodynamic, mechanical design and structural integrity analysis of the component. These design criteria, sometimes act in opposition, hence engineering balance is employed within the specified design performance limits. This paper presents the structural and conceptual design of a sixteen stage single shaft high pressure compressor of IND100 with an overall pressure ratio of 12 and mass flow of 310 kg/s at ISOSLS conditions. Furthermore, in order to evaluate the conceptual design analysis, basic parameters like compressor sizing, load and blade mass, disc stress analysis, bearings and material selections, conceptual disc design and rotor dynamics are considered using existing tools and analytical technique. These techniques employed the basic thermodynamic and aerodynamic theory of axial flow compressors to determine the temperature and pressure for all stages, geometrical parameters, velocity triangle, and weight and stress calculations of the compressor disc using Sagerser Empirical Weight Estimation. The result analysis shows a constant hub diameter annulus configuration with compressor overall axial length of 3.75 m, tip blade speed of 301 m/s, maximum blade centrifugal force stress of 170 MPa, with major emphasis on industrial application for the structural component design selections.

Effect of wire mesh casing treatment on axial compressor performance and stability

In this paper,a kind of Wire Mesh Casing Treatment(WMCT)is proposed to improve the stable operating range of the compressor.In contrast to the traditional circumferential groove,as for WMCT,a layer of wire mesh is laid on the surface of the circumferential groove.Parametric studies were conducted on the low-speed axial flow compressor,including the groove width,axial location,and mesh count.The optimum axial location for WMCT is related to its groove width.A higher wire mesh count results in a smaller compressor stall margin improvement.Steady simulations were carried out to study the effect of WMCT on the flow structure of the compressor.The wire mesh in the WMCT has a certain flow resistance,which restricts the flow into and out of the groove.Due to the WMCT,the flow parameter in the tip region of the rotor is less sensitive to changes in the operating conditions of the compressor.The WMCT causes the rotor tip blade loading to shift backward,inhibiting the formation of spill forward of the leakage flow,and thus improving the stability of the compressor.The flow resistance on the groove surface is a new degree-of-freedom for the casing treatment designer.

Experimental and Numerical Investigation of Non-synchronous Blade Vibration Excitation in a Transonic Axial Compressor

The complex flow phenomenon of rotating instability(RI) and its induced non-synchronous vibration(NSV) have become a significant challenge as they continuously increase aerodynamic load.This study aims to provide an understanding of the non-synchronous blade vibration phenomenon caused by the rotating instability of a transonic axial compressor rotor.In this case,blade vibrations and non-synchronous excitation are captured by strain gauges and unsteady wall pressure transducer sensors.Unsteady numerical simulations for a full-annulus configuration are used to obtain the non-synchronous flow excitation.The results show that the first-stage rotor blade exhibits an NSV close to the first bending mode;NSV is accompanied by a sharp increase in pressure pulsation;amplitude can reach 20%,and unsteady aerodynamic frequency will lock in a structural mode frequency when the blade vibrates in a large-amplitude motion.The predicted NSV frequency aligns well with the experimental results.The dominant mode of circumferential instability flow structure is approximately 47% of the number blades,and the cell size occupies 2-3 pitches in the circumferential direction.The full-annulus unsteady simulations demonstrate that the streamwise oscillation of the shedding and reattachment vortex structure is the main cause of NSV owing to the strong interaction between the tip leakage and separation vortices near the suction surface.

A Methodology for Assessing Axial Compressor Stability with Inlet Temperature Ramp Distortion

Based on a small perturbation stability model for periodic flow,the effects of inlet total temperature ramp distortion on the axial compressor are investigated and the compressor stability is quantitatively evaluated.In the beginning,a small perturbation stability model for the periodic flow in compressors is proposed,referring to the governing equations of the Harmonic Balance Method.This stability model is validated on a single-stage low-speed compressor TA36 with uniform inlet flow.Then,the unsteady flow of TA36 with different inlet total temperature ramps and constant back pressure is simulated based on the Harmonic Balance Method.Based on these simulations,the compressor stability is analyzed using the proposed small perturbation model.Further,the Dynamic Mode Decomposition method is employed to accurately extract pressure oscillations.The two parameters of the temperature ramp,ramp rate and Strouhal number,are discussed in this paper.The results indicate the occurrence and extension of hysteresis loops in the rows,and a decrease in compressor stability with increasing ramp rate.Compressor performance is divided into two phases,stable and limit,based on the ramp rate.Furthermore,the model predictions suggest that a decrease in period length and an increase in Strouhal number lead to improved compressor stability.The DMD results imply that for compressors with inlet temperature ramp distortion,the increase of high-order modes and oscillations at the rotor tip is always the signal of decreasing stability.

Numerical and experimental study of bleed impact in multistage axial compressors

In this study,the influence of inter-stage bleeding on the compressor performance and inter-stage flow field of a multistage axial compressor is investigated by both experimental and numerical methods.The experiment is conducted on a four-stage low-speed axial compressor,and a specific computational model is built to simulate the experiment environment accurately.To illuminate the fluid mechanisms of bleeding effect in detail,both the experiment and the simulation are carried out twice,i.e.,in the first time,the mass flow rate upstream the bleed location is constant under different bleed rate conditions;while in the second time,the mass flow rate downstream the bleed location is constant under different bleed rate conditions.The results demonstrate that inter-stage bleeding has little influence on upstream compressor characteristics,and affects the upstream flow field only in the rear half of the stator.The bleed effect on the downstream flow field is embodied in the variation of an incoming flow profile,an increase as the compressor inlet flow coefficient decreases.Therefore,such an effect is only significant on compressor characteristics at small flow coefficient conditions.In multistage compressors,the variation of compressor characteristics and flow field caused by inter-stage bleeding is the comprehensive result of the bleeding and the variation of the upstream working condition.In addition,the comparison between numerical and experimental results shows that the flow moves towards top half of span through the downstream rotor passage in the numerical simulation,whereas the trend of flow field variation with different bleed rates at the outlet of the downstream rotor and stator is the same with that at the inlet of the downstream rotor in the experiment,which means that the numerical method has overestimated the radial mixing intensity of the flow.

Modal Analysis of Axial Compressor Tip Rotating Instability under Varying Operating Conditions

The full annulus numerical research was performed on a low-speed compressor rotor to investigate the rotating instability in the tip region.The frequency spectra show the existence of rotating instability at narrow stable operating range.With the decrease of flow rate,31 cells of flow disturbance can be found in the instantaneous flow field.The distribution of vortex suggests that the circumferential propagation of the interaction between tip leakage vortex and adjacent blade brings about these cells.The dynamic mode decomposition(DMD)method and spatial discrete Fourier transform(SDFT)were applied to obtain the circumferential mode features,and the results indicate that the rotating instability is associated with the 31 cells of flow disturbance.Then the DMD method was further applied on the pressure data from a circle and an annulus domain,so as to extract different mode components with the corresponding spatial structures,frequencies and amplitudes.The results suggest that DMD modes can display the flow feature and explore the evolution of each instability source in the tip flow field.

A Review on Theoretical and Numerical Research of Axial Compressor Surge

Surge is an unstable operating condition of the aero-engine that can move the engine into a destabilized state and cause devastating damage.One of the most popular topics in the academic and industrial communities is to figure out the mechanism of the surge and withdraw from the surge safely.Based on rig test results and practical data from engine operation,various theories of surge mechanisms have been proposed by researchers,and some classical analytical models have been developed for modelling and prediction.In recent years,with the rapid development of numerical simulation and the improvement of computational capability,computational fluid dynamics(CFD)has been widely applied to the investigation of axial compressor surge events.In this review,the principles and general characteristics of the surge phenomenon are first introduced.Subsequently,the main theoretical models and CFD simulations are presented,and their advantages and disadvantages are discussed.In conclusion,we have proposed potential improvements and future technical routes for the surge phenomenon.The purpose of this paper is to provide a valuable reference for surge studies on axial compressors.

Numerical and experimental investigation of quantitative relationship between secondary flow intensity and inviscid blade force in axial compressors

The secondary flow attracts wide concerns in the aeroengine compressors since it has become one of the major loss sources in modern high-performance compressors.But the research about the quantitative relationship between secondary flow and inviscid blade force needs to be more detailed.In this paper,a database of 889 three-dimensional linear cascades was built.An indicator,called Secondary Flow Intensity(SFI),was used to express the loss caused by secondary flow.The quantitative relationship between the SFI and inviscid blade force deterioration was researched.Blade oil flow and Computation Fluid Dynamics(CFD)results of some cascades were also used to cross-validate.Results suggested that all numerical cascade cases can be divided into 3 clusters by the SFI,which are called Clusters A,B and C in the order of the increasing SFI indicator.The corner stall,known as the strong corner separation,only happens when the SFI is high.Both calculations and oil flow experiments show that the SFI would stay at a low level if the vortex core at the endwall surface does not appear.The strong interaction of Kutta condition and endwall cross-flow is considered the dominant mechanism of higher secondary flow losses,rather than the secondary flow penetration depth on the suction surface.In conclusion,the inviscid blade force spanwise deterioration is strongly related to the SFI.The correlation of the SFI and spanwise inviscid blade force deterioration is given in this paper.The correlation could provide a quantitative reference for estimating secondary flow losses in the design.

Design Optimization of Non-Axisymmetric Vane for an Axial Compressor under Inlet Distortion

The flow field at the inlet of compressors is generally encountered combined total pressure and swirl distortion for either aircraft engine with S-duct or gas turbine with lateral air intake.This inevitably deteriorates compressor aerodynamic performance,including not only the efficiency or pressure ratio but also the operation stability.In order to conquer this issue,appropriate measures such as integrating flow control techniques and modifying inlet or compressor design are of benefits.Due to this motivation,this article develops a full-annular two-dimensional(2D)and a partial-annular three-dimension(3D)optimization strategy for non-axisymmetric vane design.Firstly,two numerical simulation methods for evaluating performance of full-annular 2D vane and compressor with partial-annular 3D vane are developed.The swirl patterns at the inlet of a 1.5-stage axial compressor are analyzed and parametrized,and the parameterization is transferred to characterize the circumferential distribution of geometrical parameters of the vane profile.These approaches dramatically reduce computational simulation costs without violating the non-axisymmetric flow distortion patterns.Then various full-annular 2D sections at different radial locations are constructed as design space.The designed vane is reconstructed and 3D numerical simulations are performed to examine performance of the non-axisymmetric vane and the compressor with it.Also,partial annular 3D optimization is conducted for balancing compressor efficiency and stall margin.Results indicate that the designed non-axisymmetric vane based on full-annular optimization approach can decrease the vane total pressure loss under the considered inlet flow distortion,while those using partial-annular optimization achieve positive effects on compressor stall margin.

A stall diagnosis method based on entropy feature identification in axial compressors

A stall diagnosis method based on the entropy feature extraction algorithm is developed in axial compressors.The reliability of the proposed method is determined and a parametric sensitivity analysis is experimentally conducted for two different types of compressor stall diagnoses.A collection of time‐resolved pressure sensors is mounted circumferentially and along the chord direction to measure the dynamic pressure on the casing.Results show that the stall and prestall precursor embedded in the dynamic pressures are identified through nonlinear feature perturbation extraction using the entropy feature extraction algorithm.Further analysis demonstrates that the prestall precursor with the peak entropy value is related to the unsteady tip leakage flow for the spike‐type stall diagnosis.The modal wave inception with increasing amplitude is identified by the considerable increase of the entropy value.The flow field in the tip region indicates that the modal wave corresponds to the flow separation in the suction side of the rotor blade.The warning time is 100–300 rotor revolutions for both types of stall diagnoses,which is beneficial for stall control in different axial compressors.Moreover,a parametric study of the embedding dimension m,similar tolerance n,similar radius r,and data length N in the fuzzy entropy method is conducted to determine the optimal parameter setting for stall diagnosis.The stall warning based on the entropy feature extraction algorithm provides a new stall diagnosis approach in the axial compressor with different stall types.This stall warning can also be adopted as an online stability monitoring index when using the concept of active stall control.

Blade bowing effects on radial equilibrium of inlet flow in axial compressor cascades

The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation（CF） source item. Several simplified cascades with/without aerodynamic loading were numerically studied to investigate the effects of blade bowing on the inlet flow radial equilibrium. A data reduction program was conducted to obtain the CF source from three-dimensional（3D） simulation results. Flow parameters at the passage inlet were focused on and each term in the radial equilibrium equation was discussed quantitatively. Results indicate that the inviscid blade force is the inducement of the inlet CF due to geometrical asymmetry. Blade bowing induces variation of the inlet CF, thus changes the radial pressure gradient and leads to flow migration before leading edge（LE） in the cascades. Positive bowing drives the inlet flow to migrate from end walls to mid-span and negative bowing turns it to the reverse direction to build a new equilibrium. In addition, comparative studies indicate that the inlet Mach number and blade loading can efficiently impact the effectiveness of blade bowing on radial equilibrium in compressor design.

Alleviation of spike stall in axial compressors utilizing grooved casing treatment

Abstract This article deals with application of grooved type casing treatment for suppression of spike stall in an isolated axial compressor rotor blade row. The continuous grooved casing treatment covering the whole compressor circumference is of 1.8 mm in depth and located between 90% and 108% chord of the blade tip as measured from leading edge. The method of investigation is based on time-accurate three-dimensional full annulus numerical simulations for cases with and without casing treatment. Discretization of the Navier Stokes equations has been carried out based on an upwind second-order scheme and k-a-SST （Shear Stress Transport） turbulence modeling has been used for estimation of eddy viscosity. Time-dependent flow structure results for the smooth casing reveal that there are two criteria for spike stall inception known as leading edge spillage and trailing edge backftow, which occur at specific mass flow rates in near-stall conditions. In this case, two dominant stall cells of different sizes could be observed. The larger one is caused by the spike stall covering roughly two blade passages in the circumferential direction and about 25% span in the radial direction. Spike stall disturbances are accompanied by lower frequencies and higher amplitudes of the pressure signals. Casing treatment causes flow blockages to reduce due to allevi- ation of backflow regions, which in turn reduces the total pressure loss and increases the axial veloc- ity in the blade tip gap region, as well as tip leakage flow fluctuation at higher frequencies and lower amplitudes. Eventually, it can be concluded that the casing treatment of the stepped tip gap type could increase the stall margin of the compressor. This fact is basically due to retarding the movement of the interface region between incoming and tip leakage flows towards the rotor leading edge Diane and suttressing the reversed flow around the blade trailing edee.

Characteristics and mechanisms of turboshaft engine axial compressor casing containment

To investigate the containment characteristics and mechanisms of axial compressor blade and casing in turboshaft engine,experimental and simulation research is conducted on Titanium alloy axial compressor blades and stainless steel simulator casings in this paper.Experiments for four thicknesses(from 0.8 mm to 1.4 mm)of casings are presented on high-speed spin tester.Perforation,ricochet with and without failure of the casings are obtained in test results.Three obvious bulges or dishing region are observed,petaling failure occurs in the first bulge or the third deformation region.Parabolic and elongated dimples are observed at the fracture surface.Finite Element(FE)models with calibrated Johnson-Cook material behavior law are built and analyzed by using explicit dynamic software for a better understanding on the containment behavior.Good agreement is obtained between the experimental observations and numerical predictions.The evolution of the impact force,energy absorption,temperature increase and the cracks’propagation are analyzed.Three force peaks occur in the impact process.Energy analysis reveals that penetration condition of ricochet with failure leads to most internal energy of the casing.

Effects of the radial blade loading distribution and B parameter on the type of flow instability in a low-speed axial compressor

Previous studies showed that an axisymmetric hub-initiated disturbance defined as partial surge may initiate the stall of a transonic compressor; to reveal the instability evolution under full-span incompressible flow for different levels of hub loading and B parameter, an experimental investigation is conducted on a single-stage low-speed compressor. Experimental results show that under a uniform inflow condition without inlet flow distortion, a modal-type stall inception dominates in this low-speed compressor. When an inlet screen introducing hub distortion is used to increase the hub loading, a compressor stall is initiated by a modal wave, but large disturbances are present in the hub region before the compressor stall, which become stronger as the hub loading increases. Under high hub loading and large B parameter（implemented by adding hub distortion through an inlet screen and enlarging the outlet plenum volume, respectively）, a compressor stall is triggered by an axisymmetric hub-initiated disturbance, which is much different from the modal-like disturbances. The beginning of this axisymmetric disturbance may be captured over 800 rotor revolutions prior to the onset of stall, and the amplitude grows with time. The disturbance is hub-initiated because the disturbance signal at the hub is detected much earlier than that at the tip; meanwhile, the frequency of this axisymmetric disturbance changes with the length of the inlet duct. The characteristics of instability evolution in the low-speed compressor are also compared with those in a transonic compressor.

Using tandem blades to break loading limit of highly loaded axial compressors

It is confirmed that tandem-blade configurations have potential to enlarge the flow turning in two-dimension(2D) studies. However, the potential of tandem blades to enlarge the design space for highly loaded axial compressors was rarely investigated in open literatures. The present work aims to show the capability of tandem blades to break the loading limit of conventional blades for highly loaded compressors. The 2D models of the maximum static pressure rise derived in previous work were validated by a large amount experimental data, which showed a good agreement. An E parameter was defined to evaluate the stall margin of compressor based on the theoretical models, which indicated that the tandem blade was able to increase the loading limit of axial compressors. A single-blade stage with a loading coefficient of 0.46(based on the blade tip rotating speed) was designed as the baseline case under the guidance of the E parameter. A tandem-blade stage was then designed by ensuring that the velocity triangles were similar to the single-blade stage. The performances of both stages were investigated experimentally. The results showed that the maximum efficiency of the tandem-blade stage was 92.8%, 1% higher than the single;the stall margin increased from 16.9% to 22.3%. Besides, the maximum pressure rise of tandem rotors was beyond the loading limit of 2D single-blade cascades, which confirmed the potential of tandem blades to break the loading limit of axial compressors.

Numerical Study of the Air Bleeding Caused Non-Uniformity in Axial Compressor

Bleeding in the compressor is getting more and more attractive because the increasing demand of bleeding rate as the temperature of the first stage of turbine gets higher and needs more cooling air.Though plenty of work has been done about bleeding,however,most of the work is studied with a single passage or ignoring the real structure of the bleeding system.In the present study,multi-passage calculation was used through ANSYS CFX to consider the finite duct holes in the whole blade row,and the effect of the axial location of bleeding slot on the non-uniformity of the blade passage was investigated,and the non-uniform could maintain a low level when bleeding at the front part of the blade passage and the non-uniformity would become large when moving the bleeding slot much further downstream.Afterward,the air bleeding mass flow rate was studied.It’s found that the non-uniformity of air bleeding mass flow is small when bleeding at a low mass flow rate in each passage and results in relatively uniform flow field in the passage.However,the non-uniformity increases significantly as the bleeding mass flow rate increases.Some flow field details were also given to study how the flow field changes when bleeding non-uniformly.

A high-order model of rotating stall in axial compressors with inlet distortion

In this paper,a high-order distortion model is proposed for analyzing the rotating stall inception process induced by inlet distortion in axial compressors.A distortion-generating screen in the compressor inlet is considered.By assuming a quadratic function for the local flow total pressure-drop,the existing Mansoux model is extended to include the effects of static inlet distortion,and a new high-order distortion model is derived.To illustrate the effectiveness of the distortion model,numerical simulations are performed on an eighteenth-order model.It is demonstrated that long length-scale disturbances emerge out of the distorted background flow,and further induce the onset of rotating stall in advance.In addition,the circumferential non-uniform distribution and time evolution of the axial flow are also shown to be consistent with the existing features.It is thus shown that the high-order distortion model is capable of describing the transient behavior of stall inception and will contribute further to stall detection under inlet distortion.

Efficient Modeling of an Axial Compressor with Swirl Distortion

This paper presents a satisfactory numerical strategy to reliably evaluate the three-dimensional large-scale flow feature of multistage axial compressors in response to complex swirl distortion with acceptable computational cost. Under the theoretical framework of the body force method, the guide vanes of a swirl distortion generator and the multiple blade rows of a two-stage low-speed axial compressor are described by distributed source terms instead of a complex body-fitted grid approach. The key flow structure of the paired swirl generated by the swirl generator and the main distributions of flow angle at the rotor outlet of the first stage captured by the model agree well with experimental results, demonstrating the effectiveness of the numerical strategy. Additionally, the interaction process between the steady-state paired swirl and the compressor is clearly revealed by the study. The intensity of the swirl distortion can be greatly reduced after passing through the axial compressor. However, the swirl has a significant impact on the local blade loading of the first stage, which induces the mass flux nonuniformity as well as total pressure and total temperature distortion. The combined total pressure and total temperature distortion is significantly attenuated near tip and slightly enhanced near hub as it moves through the second stage.