Study on the effects of end-bend cantilevered stator in a 2-stage axial compressor

Leading edge recambering is applied to the cantilevered stator vanes in a 2-stage compressor in this paper. Different curving effects are produced when the end-bend stator vanes are stacked in different ways. Stacking on the leading edge induces a positive curving effect near the casing. When it is stacked on the centre of gravity, a negative curving effect takes place. The numerical investigation shows that the flow field is redistributed when the end-bend stators with leading edge stacking are applied. The variations in the stage matching for the mainstream and near the hub have an impact on the performance of the 2-stage compressor. The isentropic efficiency and the total pressure ratio of the compressor are increased near the design condition. The compressor total pressure ratio is decreased near choke and near stall. The maximum flow rate is reduced and the stall margin is decreased.     

Investigation on multiple cylindrical holes casing treatment for transonic axial compressor stability enhancement

Casing treatment is one possible way of regaining axial compressor operating range. However, most of casing treatments extend the operating range with the cost of efficiency penalty. A new form of multiple cylindrical holes casing treatment (MHCT) with pre-swirl blowing for the NASA Rotor-37 has been designed based on profound understanding of the stall inception. Unsteady numerical simulations have been performed for Rotor-37 with and without MHCT. Parametric studies of the total extraction holes area and their axial locations show that the compressor performance deteriorates as the area ratio increases but the stall margin is extended and there is an optimum extraction holes axial location for stall margin extending. The better configuration of MHCT could extend the stall margin by 6.2% with only 0.23% peak efficiency reduction. Detailed analysis of the physical mechanism behind the stall margin improvement shows that the casing treatment could eliminate the passage blockage by suppressing breakup of tip leakage vortex and decrease the blade load in tip region, which both contribute to improve stall margin of transonic axial compressors.     

Stall Behaviour in a Mixed-flow Compressor with Axial Slot Casing Treatment

Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now.To conquer this issue,unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment(ASCT).The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1%of the shaft speed,which is identical to the test data.The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT.The flow structure of the spike inception was investigated at 50%design rotational speed.Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave.Furthermore,it was found that with and without ASCT,the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge,which is different from a fraction of the centrifugal compressor.The resultant phenomenon provides conoborating evidence for that unlike in axial-flow compressor,the addition of ASCT does not change the stall characteristics of the mixed-flow compressor.The flow structure that induced spike inception with ASCT is similar to the case with smooth casing.In the throttling process,tip leakage flow vortex had been involved in the formation of tornado vortices,with one end at the suction side,and the other end at the casing-side.The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex.The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex.These results not only can provide guidance for the design of casing treatment in mixed-flow compressor,but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines.     

Effects of probe support on the stall characteristics of a low-speed axial compressor

In order to investigate the effects of probe support on the stall characteristics of micro compressors, an experiment was carried out on a large-scale low-speed research compressor according to the principle of geometric similarity. A cylindrical probe support intruding to 50% blade span was mounted at 50% chord upstream from the rotor blade leading edge. The static pressure rise characteristic of the compressor is measured, with and without the probe support respectively. The dynamic compressor behavior from pre-stall to full stall was also measured. The results indicate that the stability margin of the compressor is lowered after installing the probe support. The stall inception is aroused by modal wave disturbances. The disturbances developed into two stall cells smoothly before installing the probe support, while the disturbances first developed into a single stall cell then splitting into two stall cells after installing the probe support. The presence of probe support lowers the initial intensity of the rotating stall of the compressor, while it doesn't alter the intensity of the rotation stall after the compressor enters into full stall.     

单级离心压气机气动性能预测与优化设计

为了提升低转速工况下压气机的气动性能,采用人工神经网络与遗传算法相结合的优化方法对某单级离心压气机离心叶轮的弯特性进行优化计算。利用NUMECA软件对该离心压气机进行了不同转速的数值模拟,得到压气机不同工况下的气动性能。通过设置不同控制参数和曲线形式对离心叶轮叶片进行参数化拟合,以8个改变叶片弯特性的参数为自由参数进行了叶型优化设计,最终得到了优化后的叶轮叶片。结果表明:优化后在低转速的设计工况下离心压气机压比增加了4.69%,稳定裕度拓宽了17.41%。     

Rotating Stall and Stall-Controlled Performance of a Single Stage Subsonic Axial Compressor

Activities by various authors on aerodynamics and control dynamics of rotating stall in axial compressor are first traced. Then, a process of stall cell evolution in a subsonic stage is discussed based on a 2-D CFD. A few numbers of vortices grow ahead of the rotor accumulating vorticity ejected from lightly stalled blades, and eventually organize a cell of circumferentially aligned huge vortices, which merge and recess repeatedly during the rotation. Such stall disturbance is intensified on trailing side of a circumferential inlet distortion and decays on the leading side. Considering these features, a new algorithm for stall warning is developed based on a correlation between pressure waveforms at each passing of a fixed blade. A remarkable change in the correlation level at near-stall provides a warning signal prior to the stall onset with sufficiently large time margin. This scheme is applied to achieve rotating stall prevention by actuating flaps installed on the hub. The last issue is on characteristics of forward swept blade which has much increased throttle margin with decreased tip loss. A 3-D computation shows that a secondary vortex generated in suction surface mid span interacts to reduce the tip leakage vortex that initiates the stall.     

船用燃气轮机低压压气机改型设计研究

为了保证船用8级低压压气机在低工况稳定性不降低的前提下,同时提高设计点效率,通过数值模拟的方法研究展弦比优化对压气机设计点效率的影响。分析结果表明：展弦比的选取会影响主流区的流动损失和端壁二次流损失,进而影响压气机性能。优化了多级压气机后面级展弦比,将设计点效率提高了0.42%。同时,通过优化可转导叶偏转角度,确保了60%转速的喘振裕度不降低。     

某F级燃气轮机压气机跨音级特性计算

本文作为某F级燃气轮机轴流压气机整机特性计算的一部分,考虑到跨音级存在激波及其与附面层的相互干涉、动叶叶顶泄漏等复杂的流动现象,针对该压气机的跨音级(第一级)进行单独计算.采用NUME-CA软件对压气机内部流场进行数值计算.实际计算表明:文中使用的方法可以很好地计算出压气机全工况特性.选取近失速点、近设计点、近堵点,对...     

跨音轴流压气机动叶的三维弯掠设计研究

对一单级跨音轴流压气机中的动叶分别进行了前掠和正弯设计的参数研究,并根据研究得到的弯、掠动叶气动性能变化规律对动叶进行了前掠和正弯联合的三维设计,同时对动叶中部截面的叶型进行了二维设计以弥补弯掠动叶中部性能的降低.最终设计的跨音级性能显著提高,级最大效率提高3%,失速裕度提高40%,同时压比有所增加.数值计算结果表明,前掠和正弯叶片都可以使叶顶激波位置移向下游,降低激波强度,减轻叶顶激波与边界层和泄漏涡的作用.弯掠动叶控制激波强度和端壁流动的能力更加突出.     

船用燃气轮机低压压气机气动布局规律研究

为缩短燃气轮机低压压气机的设计周期,获取一维设计中各关键设计参数分布规律,同时得到最优的一维设计参数选取方案,采用基于HARIKA算法的压气机一维设计与分析程序对某型船用低压压气机流量系数、载荷系数和反动度的轴向布局方法进行了研究并提炼了各参数分布的数学模型。其中,流量系数和载荷系数沿级分布为近似单峰值的三次多项式曲线,反动度分布为"二段式",通过改变流量系数和载荷系数的峰值点坐标和改变特定级反动度和反动度变化步长的方法,研究了不同布局方式对效率、喘振裕度以及压比的影响,最后结合优化算法得到了最优参数分布方案。结果发现:流量系数峰值位置在第6级,载荷系数在第5级或第6级时效率和喘振裕度性能较好;第四级反动度取值0.5～0.52时效率较高;相比载荷系数和反动度,流量系数对非设计工况性能影响更为显著,优化后的参数分布方案在各转速下喘振裕度均有所提高。     

船用燃气轮机压气机多级可调静叶优化匹配方法研究

作为防止燃气轮机喘振的有效手段之一,可调静叶技术的应用能够提升压气机在非设计工况下的效率和运行范围,从而提高燃气轮机变工况下的经济性和稳定性.以某型船用三轴燃气轮机为研究对象,建立压气机一维性能分析模型与燃气轮机零维仿真模型耦合的变维度燃气轮机仿真模型,以经济性和稳定性为优化目标,通过多目标遗传算法对低压压气机多级可调...     

非轴对称进气对燃气轮机压气机性能的影响

为了探索非轴对称进气对轴流压气机运行稳定性的影响,采用数值模拟与实验验证相结合的方式,对周向进气周向畸变、径向畸变对压气机稳定的影响进行了分析和比较;并对畸变与流动失稳的关联及诱发失稳的物理机制进行了研究;为提高压气机抗畸变的能力,在叶顶实施了微喷气措施,取得了明显的拓稳效果.     

Numerical Investigation of Base-Setting of Stator’s Stagger Angles for a 15-stage Axial-Flow Compressor简

A 15-stage axial-flow compressor utilized in steel industry was studied in this paper. All the stator＇s stagger an- gles of the compressor are variable to ensure the multistage compressor operate effectively within a wide range of flow rate and meanwhile satisfy the demand for sufficient pressure ratio, adiabatic efficiency and stall margin. Three in all different base-settings of stator＇s stagger angles were presented and commercial CFD soft-ware was applied to obtain the overall performance characteristics. The results showed that both of the optimized base-settings improved the performances both in summer and winter conditions, although the adiabatic efficiency was somewhat decreased. Taking incidence angle and stage loading into consideration, differences among the three cases were analyzed in detail. On the basis of numerical computations, the performance could be effectively improved through adjusting the base-setting of stator＇s stagger angles.     

间隙变化对轴流压气机转子近失速工况叶顶流场的影响研究

为研究间隙变化对轴流压气机转子近失速工况下叶顶流场结构的影响,以轴流压气机转子Rotor37为研究对象,对其叶顶流场进行定常和非定常的数值模拟。计算结果表明：随着叶顶间隙的减小,压气机的总压比和等熵效率均有所提高,稳定运行范围扩大;2倍设计间隙下,叶尖泄漏涡经激波作用后发生膨胀破碎,堵塞来流通道,诱发压气机堵塞失速;0.5倍设计间隙下,吸力面流动分离加剧,发生回流,部分回流与来流在压力面前缘上游发生干涉,进口堵塞加剧,致使部分来流从前缘溢出,导致压气机叶尖失速;不同间隙下压气机失速过程的主导因素不同,大间隙下失速由叶尖泄漏涡破碎的非定常波动引起,小间隙下失速主要由流动分离引发的周期性前缘溢流所主导。     

Numerical Simulation of Active Suppression of Rotating Stallin Axial Compression Systems

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Stall inception process and prospects for active hub-flap control in three-stage axial flow compressor

The possibility to apply the active hub-flap control method, which is a proven rotating stall control method for a single-stage compressor, to a 3-stage axial compressor is experimentally discussed, where complex rotating stall inception processes are observed. The research compressor is a 3-stage one and could change the stagger angle settings for rotor blades and stator vanes. Sixteen rotor blade/stator vane configuration patterns were tested by changing stagger angle for the stator vanes. By measurement of surface-pressure fluctuation, stall inception proc- esses are investigated and the measured pressure fluctuation data is used as a predictive signal for rotating stall. The experimental results show that the stall detection system applied to active hub-flap control in a single-stage compressor could be usefully applied to that in a 3-stage compressor with a more complex stall inception process.     

Design and optimization of a single stage centrifugal compressor for a solar dish-Brayton system

According to the requirements of a solar dish-Brayton system,a centrifugal compressor stage with a minimum total pressure ratio of 5,an adiabatic efficiency above 75% and a surge margin more than 12% needs to be designed.A single stage,which consists of impeller,radial vaned diffuser,90° crossover and two rows of axial stators,was chosen to satisfy this system.To achieve the stage performance,an impeller with a 6:1 total pressure ratio and an adiabatic efficiency of 90% was designed and its preliminary geometry came from an in-house one-dimensional program.Radial vaned diffuser was applied downstream of the impeller.Two rows of axial stators after 90° crossover were added to guide the flow into axial direction.Since jet-wake flow,shockwave and boundary layer separation coexisted in the impeller-diffuser region,optimization on the radius ratio of radial diffuser vane inlet to impeller exit,diffuser vane inlet blade angle and number of diffuser vanes was carried out at design point.Finally,an optimized centrifugal compressor stage fulfilled the high expectations and presented proper performance.Numerical simulation showed that at design point the stage adiabatic efficiency was 79.93% and the total pressure ratio was 5.6.The surge margin was 15%.The performance map including 80%,90% and 100% design speed was also presented.     

基于叶片弯掠技术的优化设计

在三维粘性流场的数值计算程序平台上,利用BP神经网络和遗传算法,通过叶片弯掠技术对一轴流风机的转子叶片的周向弯曲角度进行寻优,以使风扇的气动性能进一步提高。通过对比优化前、后的叶轮发现,优化之后的叶片呈现明显的周向前弯曲特征。测试结果显示,其全压和气动效率分别提高了3.56%和1.27%,失速裕度大幅度拓宽36%以上,上、下端部的损失进一步降低。     

An experimental description of the flow in a centrifugal compressor from alternate stall to surge

The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines.The compressor is composed of inlet guide vanes,a backswept splittered unshrouded impeller,a splittered vaned radial diffuser and axial outlet guide vanes.Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate.This alternate flow pattern involves two adjacent vane passages.One passage exhibits very low momentum and a low pressure recovery,whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently.Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted.At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors.As the compressor is throttled the path to instability has been registered and a first scenario of the surge inception is given.The compressor first experiences a steady alternate stall in the diffuser.As the mass flow decreases,the alternate stall amplifies and triggers the mild surge in the vaned diffuser.An unsteady behavior results from the interaction of the alternate stall and the mild surge.Finally,when the pressure gradient becomes too strong,the alternate stall blows away and the compressor enters into deep surge.     

Numerical study on the influence mechanism of inlet distortion on the stall margin in a transonic axial rotor

A numerical study is conducted to investigate the influence of inlet flow condition on tip leakage flow (TLF) and stall margin in a transonic axial rotor.A commercial software package FLUENT,is used in the simulation.The rotor investigated in this paper is ND_TAC rotor,which is the rotor of one-stage transonic compressor in the University of Notre Dame.Three varied inlet flow conditions are simulated.The inlet boundary condition with hub distortion provides higher axial velocity for the incoming flow near tip region than that for the clean inflow,while the incoming main flow possesses lower axial velocity near the tip region at tip distortion inlet boundary condition.Among the total pressure ratio curves for the three inlet flow conditions,it is found that the hub dis-torted inlet boundary condition improves the stall margin,while the tip distorted inlet boundary condition dete-riorates compressor stability.The axial location of interface between tip leakage flow (TLF) and incoming main flow (MF) in the tip gap and the axial momentum ratio of TLF to MF are further examined.It is demonstrated that the axial momentum balance is the mechanism for interface movement.The hub distorted inflow could de-crease the axial momentum ratio,suppress the movement of the interface between TLF and MF towards blade leading edge plane and thus enhance compressor stability.