Numerical and performance analysis of one row transonic rotor with sweep and lean angle

In this study,aerodynamic behaviors of swept and leaned blades were investigated.Axial and tangential blade curvatures impacts on compressor＇s operating parameters were analyzed separately.A commercial CFD program which solves the Reynolds-averaged Navier-Stokes equations was used to find out the mentioned impact and the complicated flow field of transonic compressor-rotors.The CFD method that was used for solving flow field＇s equation was validated by experimental data of NASA Rotor 67.The results showed that the compressor with curved rotors had higher efficiency,rotor pressure ratio and stable operating range compared to the compressor with un-curved rotors.Using curved rotors mostly had higher impact on the overall stable operating range compared to the other operating parameters.Operating range involves choking point and stall point that were changed separately by using of bended blade.For finding the detailed impact of sweep and lean angle on transonic blades,various forms of lean and sweep angles were exerted to basic rotor.It was found that sweep angles increased overall operating range up to 30%,efficiency up to 2%and pressure ratio up to 1%.Leaning the blades increased the safe operating range,the pressure ratio and efficiency by 14%,4%and 2%respectively.     

Effects of axial non-uniform tip clearances on aerodynamic performance of a transonic axial compressor

This paper presents a numerical investigation of effects of axial non-uniform tip clearances on the aerodynamic performance of a transonic axial compressor rotor （NASA Rotor 37）. The three-dimensional steady flow field within the rotor passage was simulated with the datum tip clearance of 0.356 mm at the design wheel speed of 17188.7 rpm. The simulation results are well consistent with the measurement results, which verified the numeri- cal method. Then the three-dimensional steady flow field within the rotor passage was simulated respectively with different axial non-uniform tip clearances. The calculation results showed that optimal axial non-uniform tip clearances could improve the compressor performance, while the efficiency and the pressure ratio of the com- pressor were increased. The flow mechanism is that the axial non-uniform tip clearance can weaken the tip leak- age vortex, blow down low-energy fluids in boundary layers and reduce both flow blockage and tip loss.     

Influence of Hub Contouring on the Performance of a Transonic Axial Compressor Stage with Low Hub-Tip Ratio

The rotor blade height with low hub-tip ratio is relatively longer,and the aerodynamic parameters change drastically from hub to tip.Especially the organization of flow field at hub becomes more difficult.This paper takes a transonic 1.5-stage axial compressor with low hub-tip ratio as the research object.The influence of four types of rotor hub contouring on the performance of transonic rotor and stage is explored through numerical simulation.The three-dimensional numerical simulation results show that different hub contourings have obvious influence on the flow field of transonic compressor rotor and stage,thus affecting the compressor performance.The detailed comparison is conducted at the rotor peak efficiency point for each hub contouring.Compared with the linear hub contouring,the concave hub contouring can improve the flow capacity,improve the rotor working capacity,and increase the flow rate.The flow field near blade root and efficiency of transonic rotor is improved.The convex hub contouring will reduce the mass flow rate,pressure ratio and efficiency of the transonic rotor.Full consideration should be given to the influence of stator flow field by hub contouring.     

轴流透平机械通流部分泄漏流动及控制技术研究进展

综述了轴流透平机械通流部分泄漏流动及控制技术的研究进展,首先详细介绍了轴流透平机械特别是汽轮机通流部分的泄漏流动特性及其对通流效率的影响,接着介绍了透平机械动叶顶部间隙泄漏流动特性及其对透平级气动性能的影响的研究,讨论了考虑间隙泄漏流动对某四级工业汽轮机气动性能的影响,研究了某汽轮机高压缸平衡孔对透平级气动性能的影响及其作用机制。论文简介了透平机械流动控制技术及其研究进展,最后给出了对透平机械泄漏流动及控制技术的研究展望。     

Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

<正>It is well known that tip leakage flow has a strong effect on the compressor performance and stability. This paper reports on a numerical investigation of detailed flow structures in an isolated transonic compressor rotor-NASA Rotor 37 at near stall and stalled conditions aimed at improving understanding of changes in 3D tip leakage flow structures with rotating stall inception.Steady and unsteady 3D Navier-Stokes analyses were conducted to investigate flow structures in the same rotor.For steady analysis,the predicted results agree well with the experimental data for the estimation of compressor rotor global performance.For unsteady flow analysis, the unsteady flow nature caused by the breakdown of the tip leakage vortex in blade tip region in the transonic compressor rotor at near stall condition has been captured with a single blade passage.On the other hand, the time-accurate unsteady computations of multi-blade passage at near stall condition indicate that the unsteady breakdown of the tip leakage vortex triggered the short length-scale-spike type rotating stall inception at blade tip region.It was the forward spillage of the tip leakage flow at blade leading edge resulting in the spike stall inception. As the mass flow ratio is decreased,the rotating stall cell was further developed in the blade passage.     

用于跨声速叶轮性能计算的多种分裂格式的分析与比较

针对跨声速压气机叶片内复杂的三维流动,采用自行开发的三维CFD程序对跨音速轴流压气机NASA Rotor 37流场进行数值模拟,对比分析了L-F（Lax Friedrichs）、Steger Warming及Van Leer 3种通矢量分裂格式和AUSMDV混合格式在跨声速叶轮流场数值计算时的格式效应。研究表明：与其他格式相比,AUSMDV在设计工况下的计算结果与实验误差最小,对激波和叶顶间隙泄漏的捕捉能力最强,Van Leer格式次之;Steger Warming格式在计算过程中收敛性最好。     

Predicting wind turbine blade loads and aeroelastic response using a coupled CFD–CSD method

The aeroelastic response and the airloads of horizontal-axis wind turbine rotor blades were numerically investigated using a coupled CFD–CSD method. The blade aerodynamic loads were obtained from a Navier–Stokes CFD flow solver based on unstructured meshes. The blade elastic deformation was calculated using a FEM-based CSD solver which employs a nonlinear coupled flap-lag-torsion beam theory. The coupling of the CFD and CSD solvers was accomplished in a loosely coupled manner by exchanging the information between the two solvers at infrequent intervals. At first, the present coupled CFD–CSD method was applied to the NREL 5MW reference wind turbine rotor under steady axial flow conditions, and the mean rotor loads and the static blade deformation were compared with other predicted results. Then, the unsteady blade aerodynamic loads and the dynamic blade response due to rotor shaft tilt and tower interference were investigated, along with the influence of the gravitational force. It was found that due to the aeroelastic blade deformation, the blade aerodynamic loads are significantly reduced, and the unsteady dynamic load behaviors are also changed, particularly by the torsional deformation. From the observation of the tower interference, it was also found that the aerodynamic loads are abruptly reduced as the blades pass by the tower, resulting in oscillatory blade deformation and vibratory loads, particularly in the flapwise direction.     

Unsteady rotor-stator interaction in high speed compressor and turbine stages

The blade row interaction can alter the time-mean flow and therefore be of interest for aerodynamic design analysis. Whereas results within low subsonic turbomachines are quite numerous in the literature, there have been far fewer works which give results of blade row interaction within high speed cases. Two cases are related in this paper. First, the effects of an incoming wake on the rotor flow field of a transonic compressor are analyzed. The blade row interaction proved to be positive regarding the total pressure ratio, but negative regarding the losses. The second case concerns a transonic turbine. Particular emphasis is placed on the assessment of the deterministic correlations included in the Averaged Passage Equation System.     

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.     

高压比跨音速离心叶轮的三维叶片型线优化

应用Fine／Design3D软件,采用CFD方法对某一高压比跨音速离心叶轮进行三维叶片型线优化设计,优化结果是效率提高了1．05％,压比和流量也都得到了提高。从几何变化分析,相对于根部、中径截面叶片型线,叶片顶部型线优化是提高跨音速离心叶轮效率的有效措施。     

高负荷跨音速压气机转子气动设计及附面层抽吸研究

本文设计了一跨音速压气机转子,其叶尖切线速度420 m/s,在确保动叶出口参数的同时,压比达到3.2,绝热等熵效率88.7%。数值模拟表明,60%叶高到叶顶区域,气体分离严重。为了有效控制分离,本文初步探讨了抽吸附面层对转子性能的影响。结果表明抽气能明显影响附面层的发展与激波的空间结构,转子局部性能得到改善。     

An improvement on the efficiency of a single rotor transonic compressor by reducing the shock wave strength on the blade suction surfaces

It is well known that increasing the rotational velocity is an effective way to increase the total pressure ratio. With increasing flow velocity especially under the condition of transonic flow in the supersonic region, where exist strong shock waves, the shock wave loss becomes main and important. Simultaneously, there occurs boundary layer separation due to the shock wave / boundary layer interaction. In the present paper the transonic compressor blades were studied and analyzed to find a proper and simple way to reduce the shock wave loss by optimizing the suction surface configuration or controlling the gradient of isentropic Mach number on the suction surface. A Navier-Stokes solver combined with a modified design algorithm was developed and used. The NASA single rotor for transonic flow compressor was served as a numerical example to show the effectiveness of this method. Two cases for both original and modified rotors were analyzed and compared.     

Numerical modeling of gland seal erosion in a geothermal turbine

Excessive erosion of the low-pressure rotor end gland seal of a 25 MWe geothermal turbine produced a partial loss of turbine vacuum that degraded cycle efficiency. This study used computational fluid dynamics (CFD) to identify the causes of erosion and the optimal steam seal system flow conditions for reducing the erosion problem. The predictions were based upon a numerical calculation using a commercial CFD code (Adapco Star-CD) to model the rotor end gland seal with a steam flow containing hard solid particles. The results confirmed that flow conditions play a major role in rotor gland seal erosion. By changing steam seal flow pressures to vary flow, it was confirmed that there is a threshold seal flow condition below which erosion does not occur, or is minimized. Optimizing the rotor end gland seal supply pressure and intercondenser pressure reduced the turbulent flow kinetic energy by 49%, with a corresponding decrease in the erosion rate of the rotor gland seal surface. The erosion rate is related directly to the particle velocity and turbulent flow kinetic energy. Recommendations are provided for adjusting the rotor end gland seal system to avoid erosion.     

微小型向心涡轮转子的流动特性分析

利用三维粘性数值模拟手段分析研究了一台直径35mm、设计转速为150000r／min的向心涡轮转子的流动特性。根据计算结果，得到了设计转速下向心涡轮转子的特性曲线以及设计点参数(流量为0.064kg／s，总落压比为1.716，绝热效率为0.849，做功量9.25kW)。根据流场内的壁面极限流线、空间流线以及截面流线，分析了在这台转子叶片通道中涡系的产生、发展过程以及分离形态的演变。根据叶轮主要特征流面的流动等值线图，分析了这台涡轮转子的流动特点。在初步认识向心涡轮的流动规律之上，为这台向心涡轮转子的改进设计提供了理论依据。     

Efficiency enhancement in transonic compressor rotor blades using synthetic jets: A numerical investigation

Several passive and active techniques were studied and developed by compressor designers with the aim of improving the aerodynamic behavior of compressor blades by reducing, or even eliminating, flow separation. Fluidic-based methods, in particular, have been investigated for a long time, including both steady and unsteady suction, blowing and oscillating jets. Recently, synthetic jets (zero mass flux) have been proposed as a promising solution to reduce low-momentum fluid regions inside turbomachines. Synthetic jets, with the characteristics of zero net mass flux and non-zero momentum flux, do not require a complex system of pumps and pipes. They could be very efficient because at the suction part of the cycle the low-momentum fluid is sucked into the device, whereas in the blowing part a high-momentum jet accelerates it. To the authors’ knowledge, the use of synthetic jets has never been experimented in transonic compressor rotors, where this technique could be helpful (i) to reduce the thickness and instability of blade suction side boundary layer after the interaction with the shock, and (ii) to delay the arising of the low-momentum region which can take place from the shock-tip clearance vortex interaction at low flow operating conditions, a flow feature which is considered harmful to rotor stability. Therefore, synthetic jets could be helpful to improve both efficiency and stall margin in transonic compressor rotors. In this paper, an accurate and validated CFD model is used to simulate the aerodynamic behavior of a transonic compressor rotor with and without synthetic jets. Four technical solutions were evaluated, different for jet position and velocity, and one was investigated in detail.     

Heat transfer in high‐aspect‐ratio rectangular passage with skewed ribs

The heat transfer characteristics and flow behavior in a rectangular passage with two opposite 45° skewed ribs for turbine rotor blade have been investigated for Reynolds numbers from 7800 to 19,000. In this blade, the spanwise coolant passage at the trailing edge region whose thickness is very thin is chosen, so the channel aspect ratio (=width/height of channel) is extremely high, 4.76. Therefore the heat transfer experiment in the high‐aspect‐ratio cooling channel was performed using thermochromic liquid crystal and thermocouples. Furthermore, the calculation of flow and heat transfer was carried out using CFD analysis code to understand the heat transfer experimental results. The enhanced heat transfer coefficients on the smooth side wall at the rib's leading end were the same level as those on the rib‐roughened walls. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 89–104, 2002; DOI 10.1002/htj.10018     

Aerodynamics of swept and leaned transonic compressor-rotors

A systematic investigation to understand the impact of axially swept and tangentially leaned blades on the aerodynamic behaviour of transonic axial-flow compressor rotors was undertaken. Effects of axial and tangential blade curvature were analyzed separately. A commercial CFD package, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of transonic compressor-rotors. It was validated against NASA Rotor 37 existing experimental data. Computed performance maps and downstream profiles showed a good agreement with measured ones. Furthermore, comparisons with experimental data indicated that the overall features of three-dimensional shock structure, shock-boundary layer interaction, and wake development are calculated well by the numerical solution. Next, quite a large number of new transonic swept rotors (26) were modelled from the original Rotor 37, by changing the meridional curvature of the original stacking line through three previously defined control points (located at 33%, 67% and 100% of span). Similarly, 26 new transonic leaned rotors were modelled by changing the circumferential position of the same control points. All the new transonic rotors were simulated and the results revealed many interesting aspects which are believed to be very helpful to better understand the blade curvature effects on shock structure and secondary losses within a transonic rotor.     

Control of transonic flow fields using local occurrence of non-equilibrium condensation

Control of supersonic flow fields with shock wave is important for some industrial fields. There are many studies for control of the supersonic flow fields using active or passive control. When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by latent heat released. Many studies for the condensation have been conducted and the characteristics have been almost clarified. Further, it was found that non-equilibrium condensation can control the flow field. In these studies, the condensation occurs across the passage of the flow field and it causes the total pressure loss in the flow field. However, local occurrence of non-equilibrium condensation in the flow field may change the characteristics of total pressure loss compared with that by the condensation across the passage of the nozzle and there are few for researches of locally occurred non-equilibrium condensation in supersonic flow field. The purpose in the present study is to clarify the effect of local occurrence of non-equilibrium condensation on the transonic flow field in a nozzle with a circular bump. As a result, local occurrence of non-equilibrium condensation reduced the shock strength and total pressure loss in the transonic flow field by flowing the moist air from trailing edge of the circular bump to the mainstream.     

某型高压汽轮机动叶栅的气动优化设计

利用CFD(计算流体力学)技术对某冲动式汽轮机的高压级动叶进行了改型设计。对比数值模拟结果,优化后有效地改善了叶栅流道中的流动状况,级性能有了显著的提高。     

Investigation of the NREL phase VI experiment with the incompressible CFD solver THETA

DLR's incompressible flow solver THETA is introduced for wind turbine applications on the isolated NREL phase VI Unsteady Aerodynamic Experiment rotor. The optimization of parameter settings for the prediction of attached and separated flows on the rotor is performed, including time step size, spatial discretization scheme, turbulence models and Chimera overset grid technique. Afterwards, a systematic study on the pressure distributions, rotor thrust and rotor torque for experimental series S, I and J is performed. The accuracy of results for wind velocities between 7 and 25 m s[[EQUATION1]], covering attached, partly separated and deep stalled flow conditions, is discussed. While good to excellent agreement between THETA sectional pressure distributions and the experimental reference data is achieved in attached flow and deep stall configurations, more efforts are needed to predict partly separated flow cases with comparable accuracy. A code‐to‐code comparison with DLR's compressible flow solver TAU enabled the quantification of differences in pressure prediction because of the use of incompressible and compressible flow solvers. Copyright © 2017 John Wiley & Sons, Ltd.