Optimum Profiles of Endwall Contouring for Enhanced Net Heat Flux Reduction and Aerodynamic Performance

Successfully utilized non-axisymmetric endwalls to enhance turbine efficiencies(aerodynamic and turbine inlet temperatures)by controlling the characteristics of the secondary flow in a blade passage.This is accomplished by steady-state numerical hydrodynamics and deep knowledge of the field of flow.Because of the interaction between mainstream and purge flow contributing supplementary losses in the stage,non-axisymmetric endwalls are highly susceptible to the inception of purge flow exit compared to the flat and any advantage rapidly vanishes.The conclusions reveal that the supreme endwall pattern could yield a lowering of the gross pressure loss at the design stage and is related to the size of the top-loss location being productively lowered.This has led to diminished global thermal exchange lowered in the passage of the vane alone.The reverse flow adjacent to the suction side corner of the endwall is migrated farther from the vane surface,as the deviated pressure spread on the endwall accelerates the flow and progresses the reverse flow core still downstream.The depleted association between the tornado-like vortex and the corner vortex adjacent to the suction side corner of the endwall is the dominant mechanism of control in the contoured end wall.In this publication,we show that the non-axisymmetric endwall contouring by selective numerical shape change method at most prominent locations is advantageous in lowering the thermal load in turbines to augment the net heat flux reduction as well as the aerodynamic performance using multi-objective optimization.

Self-Adaptive Stepsize Affine Projection Based Parameter Estimation of IPMSM Using Square-Wave Current Injection

Affine projection algorithm(APA)has been used to estimate the parameters of interior permanent magnet synchronous motor(IPMSM).However,there is not a strict guideline of choosing the stepsize of this algorithm to make sure that the results of parameter estimation are convergent.In order to solve such problem,self-adaptive stepsize affine projection algorithm for parameter estimation of IPMSM is proposed in this paper.Compared with traditional affine projection algorithm,this method can obtain the stepsize automatically based on the operation condition,which can ensure the convergence and celerity of the process of parameter estimation.Then,on the basis of self-adaptive stepsize affine projection algorithm,a novel parameter estimation method based on square-wave current injection is proposed.By this method,the error of estimated parameter caused by stator resistance,linkage magnetic flux and dead-time voltage can be reduced effectively.Finally,the proposed parameter estimation method is verified by experiments on a 2.2-kW IPMSM drive platform.

端壁自适应射流对跨声速压气机近失速工况性能影响的数值研究

为了提升压气机的稳定工作裕度和近失速工况性能,提出了一种在压气机静叶端壁施加端壁自适应射流的被动控制方法。利用数值模拟方法开展了不同出口轴向位置和出口偏航角的端壁自适应射流结构对跨声速压气机级性能影响的研究。研究结果表明:端壁自适应射流结构能够有效提升压气机的稳定工作裕度,并能提高近失速工况的总压比和等熵效率,在目前综合表现最佳的端壁自适应射流方案中,稳定工作裕度改进量为27.99%,近失速工况的总压比和等熵效率分别提升了0.61%和1.07%,峰值点效率略微下降0.55%。端壁自适应射流结构能够在一定程度上抑制低能流体回流,缓解流道堵塞,降低总压损失,提升叶片负荷,射流出口位于角区分离起始位置附近的作用效果较好。

Influence of Endwall Air Injection with Discrete Holes on Corner Separation of a Compressor Cascade

The aim of this study is to reveal the influence mechanism of endwall air injection with distributed holes on the corner separation of a highly loaded compressor cascade,so as to promote the application of injection in aero-engines.Single-hole and double-hole endwall injection schemes featuring different axial locations,pitchwise locations,injection mass rates and injection directions,were designed and investigated.Results showed that the corner separation was eliminated by endwall injection;the optimal single-hole injection scheme achieved an endwall loss coefficient reduction of 29.7%,with injection coefficient as low as 0.48%.The optimal axial location of single-hole endwall injection was at 82%axial chord,being the center of corner separation.However,as injection hole was located at upstream of it,endwall injection resulted in severer corner separation.The mid-span flow field was deteriorated after endwall injection,which was due to 3D flow effects,i.e.,AVDR(axial velocity density ratio)effect and low-momentum fluid spanwise migration effect.The optimal injection was achieved at low injection angle and from close to the suction surface on pitchwise.Double-hole injection exhibited inferior performance compared with single-hole,which was due to the interaction of the two injection streams and mixing of injection streams with the bulk stream.

Experimental Study of Heat Transfer and Film Cooling Performance of Upstream Ejected Coolant on a Turbine Endwall

An upstream coolant injection that is different from the known leakage flow was introduced to protect the turbine endwall.This coolant is ejected tangentially from a row of cylindrical holes situated at the side of a backward-facing step.In this experiment,the effects of mass flow ratio and leakage slot width on the endwall heat transfer characteristics were investigated.The dimensionless heat transfer coefficient(Nu)and adiabatic film cooling effectiveness(η)on an axisymmetric turbine endwall were measured by the stable-state thermochromic liquid crystal(TLC)technique and the pressure sensitive paint(PSP)technique,respectively.Three mass flow ratios(MFR)of 0.64%,0.85%,and 1.07%,as well as two leakage slot widths(W)of 3.93 mm,and 7.86 mm were considered.Results indicate that the injection film suppresses the strength of the passage vortex,which leads to the coolant covering almost the entire endwall.This result is more evident for the higher MFR cases,meanwhile,the corresponding averaged film cooling effectiveness is increased with the enhancement of the MFR.However,the case with a higher MFR produces a higher heat transfer coefficient distribution,especially in the region close to the leakage slot edge.Besides,when the W is lower,the endwall presents a higherηand a lower Nu for all the cases,which can guide the optimal design of the endwall.

A suture-free, shape self-adaptive and bioactive PEG-Lysozyme implant for Corneal stroma defect repair and rapid vision restoration

limitation of donor tissue shortage clinically. In addition, suturing-needed transplantation potentially causes postoperative complications. Herein, we design a PEG-Lysozyme injective hydrogel as a suture-free, shape self-adaptive, bioactive implant for corneal stroma defect repair. This implant experiences a sol-gel phase transition via an in situ amidation reaction between 4-arm-PEG-NHS and lysozyme. The physicochemical properties of PEG-Lysozyme can be tuned by the components ratio, which confers the implant mimetic corneal modulus and provides tissue adhesion to endure increased intraocular pressure. In vitro tests prove that the implant is beneficial to Human corneal epithelial cells growth and migration due to the bioactivity of lysozyme. Rabbit lamellar keratoplasty experiment demonstrates that the hydrogel can be filled into defect to form a shape-adaptive implant adhered to native stroma. The implant promotes epithelialization and stroma integrity, recovering the topology of injured cornea to normal. A newly established animal forging behavior test prove a rapid visual restoration of rabbits when use implant in a suture free manner. In general, this work provides a promising preclinical practice by applicating a self-curing, shape self-adaptive and bioactive PEG-Lysozyme implant for suture-free stroma repair.

射流角和质量流量比对涡轮端壁气膜冷却特性的影响

为了提高实际燃机涡轮端壁的气膜冷却效率,对某航空发动机涡轮静叶端壁的气膜冷却特性进行了数值模拟研究。首先采用实验结果对湍流模型进行了校核,并验证了所研究模型的网格无关性,在此基础上研究了端壁离散气膜孔的气膜冷却特性,并采用给定实验端壁热流输入条件计算了整个端壁的换热特性;分析了5种冷气质量流量比(1.4%、2.1%、2.7%、3.1%、3.8%)和5种气膜冷气射流角度(20°、25°、30°、35°、40°)下端壁离散气膜孔的流动特性、气膜冷却特性以及换热特性。计算结果表明:相同射流角(40°)条件下,冷气质量流量比为1.4%时,端壁平均气膜冷却效率达到0.21;继续增大冷气质量流量比会导致气膜脱离端壁表面,使得端壁整体的气膜冷却效率下降;随着冷气质量流量比增加,叶栅通道总压损失增加,强化了气膜孔出口处的气流掺混,增加了换热效率;受到端壁二次流以及原有气膜孔结构的影响,气膜冷气射流角度为20°时冷却效果最佳,在相同质量流量比(1.4%)条件下,端壁平均气膜冷却效率达到0.27;减小射流角度对端壁表面换热强度改变较小。

喷射角对涡轮发动机导叶端壁气膜冷却的影响

采用Standard k-ε紊流模型,并结合SIMPLE算法对流场进行迭代求解。研究了燃气轮机导叶端壁圆柱形冷却孔在4种不同入射角度a=25°、a=30°、a=35°和a=45°时的端壁气膜冷却效果,并分析了典型工况下不同角度的涡量分布,以及叶片压力面、吸力面的温度场。结果表明,叶片两侧马蹄涡会夹裹着冷却射流向吸力面偏移,马蹄涡对冷却射流的影响能力随着入射角度的增大而减弱。当M=2.0,α=35°时反向对称涡作用最小,冷却效果最好。端壁冷却射流喷射时,叶片压力面会产生一个低温带。

利用端区射流调节涡轮流量的数值研究

采用三维数值模拟方法对在导叶端区射入第二股气流的涡轮流场进行计算,分析了各喷气参数(如喷气位置、角度、流量、马赫数以及总温总压等)对涡轮流量的影响规律。结果表明:涡轮流量对喷气位置相当敏感,精确的喉道位置有利于流量调节;与主流成钝角喷气对涡轮流量的调节效果较好,且喷气流量与涡轮流量的变化呈线性关系;喷气马赫数在亚声速范围内的变化基本不影响涡轮流量;高喷气总温有利于涡轮流量调节,但喷气总压对涡轮流量影响不大。

端壁运动对自发射流抑制叶尖泄漏影响的数值研究

通过数值手段分析了端壁运动对带有叶尖自发射流的叶栅流场特性、叶顶间隙泄漏流量特性及叶片周向载荷分布特性的影响。结果表明:端壁运动的反向刮削作用会显著影响间隙附近流场,随着端壁运动速度增大,泄漏涡和上通道涡会逐渐向叶片吸力面靠近,同时,泄漏涡强度逐渐削弱,而上通道涡强度逐渐增强,平均总压损失增大;端壁运动对叶尖自发射流抑制泄漏流的效果有放大作用;端壁运动会显著改变叶尖吸力面附近静压系数的分布,使其具有后加载的特性。

顺–逆向组合气膜孔在涡轮导叶端壁上的应用研究

本文利用经过试验数据验证的RANS方法,针对高压涡轮导向器端壁双排气膜冷却结构,研究了顺向以及不同顺/逆向组合气膜孔下的端壁流动和气膜冷却特性,探索了逆向孔在涡轮端壁上应用的可行性。结果表明:端壁周向整排逆向孔出流与主流的强烈掺混增强了马蹄涡和通道涡强度并降低了冷气动量,使冷气无法到达下游区域;逆向孔布置在中部近吸力侧的顺/逆向组合方案对端壁涡系影响较小,可使端壁上游冷效明显增加且下游冷效降低较少;逆向孔角度减小,冷效增加,但提升幅度有限;本文提出的顺/逆向组合孔在MFR=1~3的范围内,明显改善了顺向孔对端壁上游冷却有限的问题,使端壁65%轴向弦长之前区域气膜冷效明显提升,且对尾缘冷效的影响较小。