Aerodynamic Design and Analysis of a Low-reaction Axial Compressor Stage

There is introduced a new low-reaction, highly-loaded axial compressor design concept which is coupled with boundary layer suction method. The characteristic features of the concept are made clear through its comparison with the MIT boundary layer suction compressor. Also are pointed out the potential applications of this concept as well as its key technological problems. Based on this concept, a single-stage, low-reaction and low-speed axial compressor is constructed in association with analysis and computation of boundary layer suction on vanes with the aid of a three-dimensional numerical approach. The results attest to the effectiveness of this way to control separation in blade cascades by the boundary layer suction and the feasibility of this proposed design concept.

Flow Field Improvement by Bowed Stator Stages in a Compressor with Different Axial Gaps Under Near Stall Condition

The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.

EFFECT OF AXIAL SPACING ON COMPRESSOR STABILITY

Experimental studies are carried out at a low speed axial compressor with five different rotor/stator gaps. Analysis of the effect of axial spacing of two successive blade rows on the measured mean flow coefficient at stall inception and on the flow range of compressor under multi-cell rotating stall operating conditions proves that the stator can suppress the flow disturbance in the compressor and strengthen the stability of the compressor. Experimental data show that the stall flow coefficient decreases by reducing the axial spacing of successive blade rows. Moreover, by reducing the axial spacing, the stall pattern transition pace from multi-cell stall to single-cell stall can be shifted. And the compressor directly slips into single-cell stall at 21.0% CR axial spacing. By analyzing the pressure fluctuation closed to the surge line, it can be known that there exists an eigenfrequency where the amplitude of the oscillating pressure suddenly and dramatically increases as the compressor runs close to the surge line and this pressure disturbance is relevant to the compressor instability.

Effects of Deposition Models on Deposition and Performance Deterioration in Axial Compressor Cascade

A new particle deposition model, namely partial deposition model, is developed in order to improve the accuracy of prediction to particle deposition. Concepts of critical velocity and critical angle are proposed and used to determine whether particles are deposited or not. The comparison of numerical results calculated by partial deposition model and existing deposition model shows that the deposition distribution obtained by partial deposition model is more reasonable. Based on the predicted deposition results, the change of total pressure loss coefficient with operating time and the distribution of pressure coefficients on blade surface after 500 hours are predicted by using partial deposition model.

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.

Investigation of Stator Wake Variability in Single Stage Axial-Compressor

In this paper, we investigate the stator wake variability along the axial direction under different rotating speeds and mass flow conditions, in the terms of wake-core position, wake depth, wake width and wake velocity gradient. Experimental study is carried out in a single stage axial compressor by using Hot-wire Anemometer (HWA). Simultaneously, the numerical calculation is brought out in the same experiment rig. Firstly, we analyze the time-averaged velocity and radial vorticity at different axial positions, and explore the wake variability along the axial direction. Then, we present the effects of operation conditions on the wake-core position, and find out the inlet Mach number and incident angle are both the key influence factors of the wake-core position. Finally, we summarize four preliminary conclusions of the wake variability.

INVESTIGATING MULTISTAGE AXIAL FLOW COMPRESSOR INSTABILITIES

A numerical methodology for investigating compressor instabilities in a multistage environment is presented. The method is based on a stage-by-stage dynamic compression model and considers air compressibility explicitly throughout the compressor. It involves discretizing the compression system into distinct elements and a use of the local elemental characteristic of mean performance. The models are presented in both nonlinear and linearized forms. The linearised form permits well surge condition prediction for multistage axial compressors, while the non-linear form is able to investigate the growth of local flow disturbances, and helps to develop practical control strategy. Validations were carried out using the data from several aircraft engine compressors. A good experiment-model consistency is achieved.

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.

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.

NUMERICAL INVESTIGATION OF AXIAL FLOW COMPRESSOR CASING TREATMENT

Using an inviscid model with inlet total pressure gradient and a J. D. Denton scheme, this paper for the first time numerically solves the 3D flow field of compressor casing treatment, and also explores some boundary singularities and numerical stability. Agreement is attained in qualitative explanations of some, casing treatment test results and its mechanism.

NEW SCALING METHOD FOR COMPRESSOR MAPS USING AVERAGE INFINITESIMAL STAGE

The estimation of the precise performance of existing multistage axial-flow compressors of gas turbine engines is fast becoming a great concern, as the use of gas turbine engines in the power generation and in the military industry increases, in order to reduce the analysis performance error of the traditional scaling method, a new scaling method for estimating the characteristics of multistage axial flow compressors is proposed. This novel method is based on experimental and partial data provided by engine manufacturers. Taking the effect of density-change into account, we introduce the average infinitesimal stage concept, and thereby divide the compression process into an infinite number of infinitesimal processes corresponding to infinitesimal stages. Subsequently, we adopt the corrected Reynolds analogy method for compressible flow calculation in order to ensure much better compliance with the similarity criterion, Validation checks show that the proposed method has enough precision to predict the off-design performance characteristics of multistage axial flow compressors.

Effects of circumferential configuration concerning splitter blade on the aerodynamic performance in a transonic axial fan

For a certain type of transonic axial fan, the flow field of a fan rotor with splitter blade was computed by numerical simulation, and the shape of the rotor was modified. The effects of different circumferential distributions concerning the splitter cascades upon the aerodynamic performance were investigated. The studies show that the optimum splitter cascade is not very close to the suction side of main blade. The load between the main blade and the splitter blade can be soundly distributed in terms of the adjustment of circumferential position of the splitter blade. The best aerodynamic performance can be successfully obtained according to the optimum shape of the expanding fluid channel reasonably formed by the splitter blade and the main blade.

Compressor Map Prediction by Neural Networks

This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for prediction of pressure ratio, compressor mass flow and mechanical efficiency. Except for evaluation of interpolation and extrapolation capabilities, this study also investigates the effect of the design parameters such as number of neurons and size of training data. To reduce the effect of noise, the auto associative neural network has been applied for noise filtering of the data from the parameters used to calculate the efficiency. In summary, the results show that artificial neural network can be used for compressor map prediction, but it should be emphasized that the selection of data normalisation scale is crucial for the model where compressor mass flow is predicted. Furthermore, it is shown that the AANN （auto associative neural network） can be used to the reduce noise in measured data and thereby enhance the quality of the data.

叶顶间隙对多级轴流压气机性能退化的影响

以某F级燃机压气机为研究对象,考虑燃机实际运行过程中腐蚀和磨损作用导致的压气机叶顶间隙变化,通过三维数值模拟方法开展了不同腐蚀/磨损状态下多级轴流压气机的性能退化机理研究,分析了叶顶间隙变化对多级轴流压气机性能的影响规律。结果表明:叶顶间隙增大会导致压气机特性曲线整体向质量流量减小的方向偏移,使得压气机的质量流量、效率及压比均产生一定程度的衰退;随着叶顶间隙的增大,压气机峰值效率逐渐降低,喘振裕度明显降低;叶顶间隙增大会导致压气机通道内的流动分离加剧,动叶叶顶间隙变化对压气机流动分离的影响更严重;静叶吸力面尾缘附近的流动分离导致形成低马赫数区,同时逆流的低速涡团导致叶根附近的损失显著增大,造成压气机性能衰退。

离心式压气机变工况模拟及轴向力变化机理分析

在相继增压系统切换过程中增压器轴向力的变化会严重影响其稳定性,以Garrett TBP4增压器的压气机端为研究对象,建立了压气机全流道计算域并划分多面体网格,设计7个工况,利用CFD研究了相继增压系统切换过程中的切换时间、切换转速、切换出口压力变化对压气机轴向力的影响规律,同时结合内部流场分析轴向力变化机理。结果表明:切换时间主要影响轴向力的突增时刻,切换转速幅值主要影响最终轴向力的大小,切换出口压力幅值主要影响轴向力突增与否;叶片轴向力受流场影响最大。

轴流压气机串列叶栅前后叶型位置匹配特性研究

采用数值和试验相结合的方法研究了高负荷轴流压气机串列叶栅前后叶型位置的匹配特性,详细分析了周向节距比和轴向重叠度2个参数对叶栅性能的影响规律和机理。结果表明,串列叶栅性能受周向节距比的影响较轴向重叠度更为显著,且在周向节距比的最优设计空间内,串列叶栅性能不再随2个参数的改变发生显著变化。周向节距比增大使缝隙流道收敛度和缝隙射流加速比增大,改变了前叶尾缘压力面和后叶前缘吸力面附近的流动特性,使前叶尾缘负荷增加,后叶前缘负荷和攻角降低,进而减弱了后叶吸力面分离。当周向节距比增大到缝隙流道闭合边界附近时,缝隙射流动量的显著降低导致分离损失显著增大。最后,采用叶栅风洞吹风试验,验证了数值计算得到的部分典型周向节距比和轴向重叠度匹配方案研究结果的可靠性。

一种降低燃气轮机试验平台启动系统功率的方法

采用轴流压气机作为负载单元的燃气轮机试验平台,启动系统-负载-燃气轮机之间采用柔性联轴器联接。启动阶段,随着机组转速的提高,轴流压气机的功耗逐渐增大。文章通过对比升速阶段燃气轮机常规启动、变工况启动两种方式对启动系统的功率需求,得出大幅降低启动功率的方式,为以后燃气轮机带负荷试验平台设计提供了参考和经验。

背压扰动平衡盘对涡旋压缩机黏性内流压力影响研究

在变转速工况下,电动涡旋压缩机背压腔中润滑油产生的背压力无法准确平衡轴向气体力。针对这一问题,提出了一种带有扰动片的背压扰动平衡盘,研究了背压扰动平衡盘对涡旋压缩机黏性内流压力的影响。首先,对背压扰动平衡盘作用原理进行了分析,使用贝塞尔曲线构建了扰动片型线,对润滑油被扰动后的静压增量进行了公式推导,计算了扰动片出口安装角和扰动片数对润滑油静压的影响;然后,建立了含背压扰动平衡盘的背压腔模型,将流体域分为旋转域和静止域,采用旋转坐标系的方法进行了数值模拟,研究了背压腔内润滑油的压力场;最后,根据理论计算,模拟了润滑油在不同出口安装角和扰动片数下的润滑油静压,对润滑油静压与压缩机所需最佳背压进行了对比分析。研究结果表明:采用背压扰动平衡盘可以使润滑油静压增加21%,且静压增量随主轴转速的增加而增大,适当增大扰动片出口安装角可使润滑油静压增加0.032 MPa;对比最佳背压可知,扰动前润滑油静压与最佳背压相差26%,而合理设计扰动片后的润滑油静压与最佳背压相差仅为9%,极大改善了电动涡旋压缩机在变转速下的轴向平衡。

引气量对多级轴流压气机性能影响的数值研究

以NASA 74A压气机前3.5级为研究对象,利用源项法探究级间引气量变化对压气机总体性能和内部流动的影响。结果表明:引气量越大压气机总体特性变化越显著,10%引气量下压气机流量范围拓宽25.72%,相比于未引气的压气机最高效率点效率增加5.6%,压比增加2.76%,而引气后进口气流冲角减小以及叶背处流动分离减弱所带来的气体流通量的增加是效率提升的主要原因;引气使得压气机稳定裕度升高,当最佳引气量8%时其稳定裕度增大21.80%;引气提高了压气机进口流量,但两者变化量不完全一致,在最高效率点处引气,引气量与进口质量流量增加量基本相等,然而,当低于最高效率点流量时,小流量点的增加量大于引气量,而大流量点则相反,这决定了出口流量的增减,影响了压气机总压比;引气对于气流周向角度影响更大,对径向角度的影响主要集中于引气位置附近。

基于范诺流理论的变截面涡旋压缩机轴向间隙泄漏研究

为了定量研究变截面涡旋压缩机轴向间隙泄漏,基于范诺流理论,考虑其主轴转速、介质粘度和摩擦等因素,探索建立变截面涡旋压缩机轴向间隙泄漏量计算模型,根据模型分析影响泄漏的主要参数,以便利用控制关键参数来降低轴向间隙泄漏。通过搭建涡旋压缩机试验平台,测定涡旋压缩机工作腔在实际工况下,不同间隙同一主轴转速和同一间隙不同主轴转速下泄漏量的实测值。结果分析表明:压差大小与泄漏量成正比,当主轴转速一定,间隙为0.02 mm时,实测值与理论值拟合较好,并且随着压差增大,泄漏变化较小;主轴转速越高,间隙泄漏量越小,当间隙一定,转速为3000 r/min时,实测值与理论值拟合较好,并且转速越高,泄漏量越大。通过理论计算与实际测量结果对比分析,所建立的泄漏量计算模型准确可靠。此模型的建立为深入研究和控制轴向间隙泄漏奠定基础,也为推广涡旋压缩机在大功率领域的应用提供理论基础。