Cathode design investigation based on iterative correction of predicted profile errors in electrochemical machining of compressor blades

Electrochemical machining (ECM) is an effective and economical manufacturing method for machining hard-to-cut metal materials that are often used in the aerospace field. Cathode design is very complicated in ECM and is a core problem influencing machining accuracy, especially for complex profiles such as compressor blades in aero engines. A new cathode design method based on iterative correction of predicted profile errors in blade ECM is proposed in this paper. A mathematical model is first built according to the ECM shaping law, and a simulation is then carried out using ANSYS software. A dynamic forming process is obtained and machining gap distributions at different stages are analyzed. Additionally, the simulation deviation between the prediction profile and model is improved by the new method through correcting the initial cathode profile. Furthermore, validation experiments are conducted using cathodes designed before and after the simulation correction. Machining accuracy for the optimal cathode is improved markedly compared with that for the initial cathode. The experimental results illustrate the suitability of the new method and that it can also be applied to other complex engine components such as diffusers. (C) 2016 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics.

Investigation on damage mechanism of compressor blades in turboshaft engine induced by ice impacts at various locations

Ice causes impact damage to different positions of the compressor blade,destroys the structural integrity of the rotor structure,and then causes unbalanced failure and even causes nonlinear vibration accidents such as collision and friction,which affects the execution of helicopter tasks.To investigate the influence of impact position on the damage form and dynamic response of blades during ice impact,a dynamic model by finite element-smooth particle fluid dynamic coupling method is created.The ice impact damage experiment of the TC4 plate based on the air gun experimental platform was carried out to verify the reliability of the simulation model.The damage of compressor blades impacted by ice from different positions under static and design speed of 45000 r/min is analyzed.The research results indicate that under static conditions,the damage caused by ice impact from the leading edge blade tip to the leading edge blade root first increases and then decreases,with the maximum damage occurring at the 66.7%blade height position on the leading edge.At the design speed,the closer the impact locations are to the leaf tip,the greater the damage is,and the plastic damage,equivalent stress,and kinetic energy loss of the ice impact are lower than the blade static condition.The research conclusion can provide theoretical reference and data support for the design of structural strength and protection of compressor blades in turboshaft engines.

Vibration reliability analysis for aeroengine compressor blade based on support vector machine response surface method

To ameliorate reliability analysis efficiency for aeroengine components, such as compressor blade, support vector machine response surface method(SRSM) is proposed. SRSM integrates the advantages of support vector machine(SVM) and traditional response surface method(RSM), and utilizes experimental samples to construct a suitable response surface function(RSF) to replace the complicated and abstract finite element model. Moreover, the randomness of material parameters, structural dimension and operating condition are considered during extracting data so that the response surface function is more agreeable to the practical model. The results indicate that based on the same experimental data, SRSM has come closer than RSM reliability to approximating Monte Carlo method(MCM); while SRSM(17.296 s) needs far less running time than MCM(10958 s) and RSM(9840 s). Therefore,under the same simulation conditions, SRSM has the largest analysis efficiency, and can be considered a feasible and valid method to analyze structural reliability.

Nonlinear Pre⁃deformation Method for Compressor Rotor Blade

A cold compressor blade deforms elastically under aerodynamic and centrifugal loads during operation,transforming into a hot blade configuration.Blade deformation has a significant effect on the performance of compressor.A nonlinear pre⁃deformation method for compressor rotor blade was developed with consideration of the nonlinear features of blade stiffness and load which varies with blade configuration.In the blade profile design phase,the method can be used to compensate the aeroelastic deformation of the blade during operation.The adverse effects of blade deflection on compressor performance and structure can be avoided by the pre⁃deformation method.Due to the fact that the nonlinear method is sensitive to initial value,a load incremental method was applied to calculate initial blade deformation to stabilize and accelerate the pre⁃deformation method.The developed method was used to predict the manufactured configuration of the Stage 37 rotor blade.The variation rules of aerodynamic and structure parameters of the pre⁃deformed blade were analyzed under off⁃design conditions.Results show that the developed method ensures that under the design condition there was a good match between the actual blade configuration during operation and the intended design blade profile.The blade untwist angle of pre⁃deformed blade could be 0°at design point.Meanwhile,the tip clearance only decreased 0.2%.When the working speed was faster than 80%design speed,the performance of the pre⁃deformed blade agreed with that of the design blade.However,the mass flow rate and the total pressure ratio of the pre⁃deformed blade were lower at low speeds.

Investigation of Microstructure of Fine Grain Cast IN718 Compressor Blade from Abroad

Fine grain cast IN718 compressor blade form abroad has been analyzed. There is no columnar grain, uniform equiaxed grain, less segregation and no porosity cast defect in essence in the section of blade body with fine grain, in which grain size is about ASTM 2 ～4. Its microstructure is approachable to that of forging. It is hopeful to achieve the goal of replacing forging by casting.

Vibration Modal Analysis of Compressor Blade based on ANSYS

Compressor is an important part of aero engine. In the environment of high temperature and high pressure,compressor blade will suffer from several physical and chemical processes,such as centrifugal force,aerodynamic force vibration and oxidation. These processes will lead compressor blade to fatigue fracture,and at the same time,make negative effects on the engine’ s overall performance. Based on the software ANSYS15. 0,we made strength analysis and modal analysis of compressor blade in this paper. As a result,we got its natural frequencies,relevant modal parameters and vibration mode cloud pictures. After analyzing the influence that centrifugal force made on modal parameters,we predicted the expected damage of the blade. Eventually the analysis results will provide the basis for overall performance evaluation,structural crack detection,fatigue life estimation and strength calculation of aircraft engine compressor.

Aerodynamics of a Tandem-Bladed Axial Compressor Rotor under Circumferential Distortion at Different Rotational Speeds

For most aircraft engines,inflow distortion is inevitable.Inflow distortion is known to degrade the aerodynamic performance and stable operating limits of a compressor.Tandem rotor configuration is an arrangement that effectively controls the growth of the boundary layer over the suction surface of the blade.Therefore,a higher total pressure rise can be achieved through this unconventional design approach involving the splitting of the blade into forward and aft sections.It is expected that the effect of inlet flow distortion would be more severe for a tandem-rotor design due to the greater flow turning inherent in such designs.However,this aspect needs to be thoroughly examined.The present study discusses the effect of circumferential distortion on the tandem-rotor at different rotational speeds.Full-annulus RANS simulations using ANSYS CFX are used in the present study.The performance of the rotor at a particular flow coefficient and different rotational speeds is compared.The total pressure and efficiency are observed to drop at lower mass flow rates under the influence of circumferential distortion.The loss region in each blade passage is mainly associated with the blade wake,tip leakage vortex,secondary flow,and boundary layer.However,their contribution varies from passage to passage,particularly in the distorted sector.At the lower span,the wake width is found to be higher than that at a higher span.Due to the redistribution of the mass flow,the circumferential extent reduces at a higher span.In the undistorted sector,the strength of the tip leakage vortex is significantly higher at the design rotational speed than at lower speeds.The distortion near the tip region promotes an early vortex breakdown even at the design operating condition.This adversely affects the total pressure,efficiency,and stall margin.Under clean flow conditions,this phenomenon is only observed near the stall point.At the design operating condition,the breakdown of the forward rotor tip leakage vortex is detected in four blade passages.The axial velocity deficit and adverse pressure gradient play a significant role in the behaviour of tip leakage vortex at lower rotational speeds in the distorted sector.A twin vortex breakdown is also observed at lower speeds.

折合频率对三维跨声速压气机颤振稳定性的影响

It is well known that fan/compressor blade flutter stability increases with the increase of reduced frequency.Less well-known is that the least stable inter blade phase angle(IBPA)increases with the drop of reduced frequency.However,it is quite striking that little can be found in the open literature about the mechanism to the observations.In this paper,a numerical investigation is carried out to uncover the mechanism of the effect of reduced frequency on flutter stability and the least stable IBPA.The NASA rotor 67 has been used as the test vehicle with its first bending and torsion modes being considered.The time domain harmonic balance method together with the influence coefficient method is used to obtain the worksum-IBPA curves for all cases.It is found that:1)the deterioration of flutter stability with the decrease of reduced frequency is dictated by the dominant decrease of aerodamping due to a blade own vibration;2)the increase of the least stable IBPA with the decrease of reduced frequency arises largely from the increase of the least stable IBPA of the aerodamping from the nearest blade on a blade pressure side.

Effect of blade sweep on inlet flow in axial compressor cascades

This paper presents comparative numerical studies to investigate the effects of blade sweep on inlet flow in axial compressor cascades. A series of swept and straight cascades was modeled in order to obtain a general understanding of the inlet flow field that is induced by sweep.A computational fluid dynamics（CFD） package was used to simulate the cascades and obtain the required three-dimensional（3D） flow parameters. A circumferentially averaged method was introduced which provided the circumferential fluctuation（CF） terms in the momentum equation.A program for data reduction was conducted to obtain a circumferentially averaged flow field.The influences of the inlet flow fields of the cascades were studied and spanwise distributions of each term in the momentum equation were analyzed. The results indicate that blade sweep does affect inlet radial equilibrium. The characteristic of radial fluid transfer is changed and thus influencing the axial velocity distributions. The inlet flow field varies mainly due to the combined effect of the radial pressure gradient and the CF component. The axial velocity varies consistently with the incidence variation induced by the sweep, as observed in the previous literature. In addition, factors that might influence the radial equilibrium such as blade camber angles, solidity and the effect of the distance from the leading edge are also taken into consideration and comparatively analyzed.

A Phased Aerodynamic Optimization Method for Compressors Based on Multi-Degrees-of-Freedom Surface Parameterization

High-fidelity aerodynamic optimization of compressors is afflicted by the"curse of dimensionality",which limits its engineering applications.This paper proposes a new multi-degrees-of-freedom(MDOF)surface parameterization method that combines the characteristics of conventional surface parameterization methods,low-dimensionality and surface smoothness,with the advantages of design flexibility and ease of construction.The proposed method is applied to the high-fidelity aerodynamic optimization of Rotor37.An optimized solution is obtained within 111 h by combining a phased optimization strategy based on the idea of modal optimization.To explore a better way of setting the control variables of the blade body,two methods of varying the control points of the suction and pressure surfaces,independent change and synchronous change,are compared.Synchronous change has better flexibility,and under the condition of satisfying the constraints,it increases the efficiency at the design point by 2.2%and the surge margin by 0.5%.This demonstrates the effectiveness of the proposed method in the high-fidelity aerodynamic optimization of compressors.It also provides technical support to solve the"curse of dimensionality"problem.

Method for utilizing PIV to investigate high curvature and acceleration boundary layer flows around the compressor blade leading edge

Particle Image Velocimetry(PIV)is a well-developed and contactless technique in experimental fluid mechanics,but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy improvement.This paper presents a data processing procedure combining conventional PIV and newly developed Mirror Interchange(MI)based Interface-PIV for the measurement of the boundary layer parameter development in the blade leading edge region.The synthetic particle images are used to analyze the measurement errors in the entire procedure.Overall,three types of errors,namely the errors caused by the Window Deformation Iterative Multigrid(WIDIM)algorithm,the discrete data interpolation and integration,and the wall offset uncertainty,comprise the main measurement error.Specifically,the errors due to the discrete data interpolation and integration and the WIDIM algorithm comprise the mean bias,which can be corrected through the error analysis method proposed in the present work.Meanwhile,the errors due to the WIDIM algorithm and the wall offset uncertainty contribute to the measurement uncertainty.Computational fluid dynamics-based synthetic particle flows were generated to verify the newly developed PIV data processing procedure and the corresponding error analysis method.Results showed that the data processing method could improve the accuracy of PIV measurements for boundary layer flows with high curvature and acceleration and even with significant flow separation bubbles.Finally,the data processing method is also applied in a PIV experiment to investigate the boundary layer flows around a compressor blade leading edge,and several credible boundary flow parameters were obtained.

Effects of Heat Transfer on Laminar-to-Turbulent Transition over a Compressor Blade Operating at Low Reynolds Number

To control the transition process in a laminar separation bubble(LSB)over an ultra-high load compressor blade at a Re of 1.5×10^(5),the effects of wall heat transfer were considered and numerically investigated by large eddy simulations(LES).Compared with the adiabatic wall condition,the local kinematic viscosity of airflow was reduced by wall cooling;thus the effects of turbulent dissipation on the growth of fluctuations were weakened.As such,the transition occurred much earlier,and the size of LSB became smaller.On the cooled surface,the spanwise vortices deformed much more rapidly and the size of hairpin vortex structures was decreased.Furthermore,the rolling-up of 3D hairpin vortices and the ejection and sweeping process very close to the blade surface was weakened.Correspondingly,the aerodynamic losses of the compressor blade were reduced by 18.2%and 38.4%for the two cooled wall conditions.The results demonstrated the feasibility of wall cooling in controlling the transition within an LSB and reducing the aerodynamic loss of an ultra-highly loaded compressor blade.

Evaluation of vibration stress of TA11 titanium alloy blade by quantitative fractography

Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimation methods by quantitative fractography were studied through experimental blade and in-service first-stage compressor blade in order to evaluate the initiation vibration stress of in-service blade. The analysis process of initiation vibration stress was established. The evaluating result of vibration stress of in-service blade subjected to centrifugal force and bending vibration stress agrees with aero engine test result. It is shown that the evaluation method can not only evaluate the equivalent fatigue stresses of different crack depths but also yield the initiation equivalent fatigue stress.

Experimental investigation of tandem rotor under clean and radially distorted inflows

With increasing emphasis on renewable sources of energy,the gas turbine engine faces several challenges in evolving its design,to remain relevant.Compressor is one of the main components,which accounts for one-third of the engine length.Compressor designers have been exploring different ideas to achieve maximum pressure rise with minimum number of stages required.Tandem blading is one such novel design that has demonstrated higher diffusion capability than a single rotor blade.A single blade,with a higher diffusion factor,carries the risk of flow separation against the adverse pressure gradient of the compressor flow.In the tandem blading concept,a single blade is split into forward and aft blade.The gap that is created between the forward and aft blade,serves as a mechanism to energize the sluggish flow over the aft blade suction surface,which in turn helps in mitigating the flow separation.The present experimental work is aimed at exploring the feasibility of a tandem rotor in an axial flow compressor under the clean and radially distorted inflows.Steady and unsteady experimental results of the tandem rotor are included in this paper.The stage performance characteristics,variation of total pressure,flow coefficient,and exit flow angle along the blade span for clean and distorted flow is included in this paper.Some results of a steady Reynolds-averaged Navier-Stokes simulation are also included to give some insight into the complex flow field of the tandem rotor.Wavelet transform,fast Fourier transform analysis,and visual inspection of casing pressure traces are used to analyze the unsteady result of the tandem rotor in clean and distorted flow.The tandem rotor is able to achieve its design pressure ratio and has a stall margin of 9%under the clean flow condition.Initially,stall appears as a low-intensity spike for all the cases,which turns into a long length-scale disturbance within three rotor revolutions.A modal wave of low frequency is also observed under clean and distorted inflows.