Numerical investigation of heat transfer coefficient in a low speed 1.5-stage turbine

The paper numerically investigated the heat transfer coefficients over the rotating blades in a 1.5-stage turbine. The hexahedral structured grids and k-ε turbulence model were applied in the simulation. A film hole with diameter of 0.004 m, angled 36°and 28° tangentially to the suction side and pressure side in streamwise respectively, was set in the middle span of the rotor blade. Simulations are done at three different rotating numbers of 0.0239, 0.0265 and 0.0280 with the blowing ratio varying from 0.5 to 2.0. The effects of mainstream Reynolds number and density ratio are also compared. Results show that increasing blowing ratio can increase the heat transfer coefficient ratio on the pressure side, but the rule is parabola on the suction side. Besides, increasing rotating number and Reynolds number is positive while increasing density ratio is negative to the heat transfer on both the pressure side and the suction side.     

Quantification of the effects of geometric approximations on the performance of a vertical axis wind turbine

With the soaring energy demands, an urge to explore the alternate and renewable energy resources has become the focal point of various active research fronts. The scientific community is revisiting the inkling to tap the wind resources in more rigorous and novel ways. Recent idea of net-zero buildings has prompted the realization of novel ideas such as employment of omni-directional vertical-axis wind turbine (VAWT) for roof-top application etc. Generally, owing to the high computational cost and time, different levels of geometric simplifications are considered in numerical studies. It becomes very important to quantify the effect of these approximations for realistic and logical conclusions. The detailed performance of a 2.5 m diameter VAWT is sequentially presented with various levels of approximations spanning from two-dimensional to complete three-dimensional geometry. The performance along with the flow physics with focus on tip effects, spanwise flow effects, effect of supporting arms and central hub is discussed. We conclude that two-dimensional approximation can over predict the performance by 32%. Similar trend is also observed for other geometric and flow approximations.     

A numerical study of geometric effects on the performance characteristics of shell-and-tube methanol reformers

Methanol reforming is a key method of producing hydrogen, an eco-friendly energy source. A feasible validation has been performed using previous experimental data. Present numerical model, validated using previously published experimental data, facilitates a factor-by-factor study of methanol reforming performance characteristics. In particular, the effects of inlet temperature of reformed gas and heat source gas, gas hourly space velocity (GHSV), reformer length, and reformer diameter are numerically analyzed. The effect of each parameter on reforming performance was presented by analyzing the average temperature of the reformed gas for each location inside the reformer. In addition, the inlet temperature of the heat source gas was more dominant in reforming performance than that of the reformed gas through sensitivity analysis. Finally, the performance was explained in terms of residence time, and the relationship between CO selectivity and residence time was presented.     

Heat transfer and aerodynamics of complex shroud leakage flows in a low-pressure turbine

A numerical investigation on over-shroud & inter-shroud leakage flow has been carried out to explore the underneath flow physics at the stage of shrouded Low Pressure(LP) turbine.Compared with the No inter-Shroud gap’s Leakage flow Model(NSLM) and With inter-Shroud gap’s Leakage flow Model(WSLM),the aerodynamic characteristics and the heat transfer performance have been studied.Through the aerodynamic point of view,it is concluded that due to the pressure difference between the rotor’s passage and the over-shroud cavity,in the stream-wise direction,flow structure has been modified,and the inter-shroud leakage flow may even cause flow separation in the vicinity of the blade passage’s throat.In the circumferential direction,separation flows appear over the rotor’s shroud surface(upper platform of the shroud).Meanwhile,from the point of view of heat transfer,further provision on contour maps of the non-dimensional Nusselt number reveals that the reattachment of leakage flow would enhance the heat transfer rates and endanger the rotor’s labyrinth fins over the shroud.However,due to the limited amount of inter-shroud leakage flow(current computational model),temperature distribution variation along the blade surface(near the rotor’s tip section) seems to have only minor insignificant differences.At the end of the paper,the author puts forward some recommendations for the purpose of future successful turbine design.     

Measurements of a 2-Stage Axial Turbine with Shrouded Rotor Cavities

This paper presents preliminary measurements of a 2-stage axial turbine with shrouded rotor cavities. The research facility and measurement techniques are reported. The flow field at both inlet and outlet was measured using 5-hole probes as well as temperature probes. The measurement results indicate that the inlet flow field is periodical in the tangential direction due to the influence of the first-stator leading-edge. The horse-shoe vortexes cause substantial flow blockage and turbulence near the endwall. Unsteady measurements of the rotor radial tip clearance show that one of the second-rotor blades has a little bigger clearance than the others.     

海洋温差能向心透平的气动设计及性能研究

通过对7.5 kW海洋温差能向心透平的蜗壳、喷嘴和叶轮进行气动设计,模拟研究了透平在设计工况及非设计工况下的气动性能。采用经验参数及遗传算法优化方法对透平的一维参数进行设计,得到一维设计结果,并据此对蜗壳、喷嘴和叶轮进行三维设计,得到透平的气动结构造型。利用CFD技术模拟研究了透平的三维流场及性能,得到透平在设计工况及非设计工况下的性能,模拟结果表明:在设计工况下,透平效率为86.5%;在非设计工况下,透平效率随着叶轮转速的增加而增大,但增加至设计转速后,透平效率增加幅度较小;随着进口温度的升高,透平效率逐渐增大;当进口压力为设计工况压力时,透平效率存在最大值;非设计工况下的透平功率基本与叶轮转速、进口压力和进口温度均呈正相关;设计工况下的最佳喷嘴-叶轮相对径向间隙为0.05,可变喷嘴叶片安装角为35～40°。     

Computational study of a new scheme for a film-cooling hole on convex surface of turbine blades

An investigation on a heart-shaped film cooling hole is performed for one row, two staggered rows, and three staggered rows on a convex surface. The results are compared with those obtained from a simple cylinder hole as a baseline. Three-dimensional computational study for two heart-shaped holes of two crown angles, φ = 60° and φ = 90°, is conducted to ascertain adiabatic film cooling effectiveness to validate whether a heart-shaped cooling hole mitigates the vortexes responsible for the lift-off phenomenon in conventional simple cylinder hole. This paper also attempts to show that the staggered arrangement of a heart-shaped hole provides higher cooling performance. The result reveals that a heart-shaped hole highly mitigates the vortexes, thereby providing more coolant-surface attachment. The results reflect the tremendous increment in centerline and lateral adiabatic film cooling effectiveness for both crown angles, φ = 60° and φ = 90°. The heart-shaped hole of crown angle φ = 60° shows higher centerline effectiveness compared with that of the heart-shaped hole crown angle of φ = 90°. The latter provides higher lateral effectiveness. The relatively small volume and high effectiveness of the heart-shaped cooling hole is important and promising for the aero engine industry.     

Geometry Effects on Aerodynamics Performance of a Low Aspect Ratio Turbine Nozzle

This paper describes the influence of some geometric parameters on aerodynamics performance of a low-aspect-ratio turbine blading designed by a novel method developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. This is a part of the study on aerodynamics optimization of turbomachinery. It follows the development of the basic ideas in the turbomachinery aerodynamics research project at the institute. The present paper concentrates mainly on the effects of geometry, such as stagger angle, leading and trailing edge thickness, maximum thickness and its location on adiabatic efficiency, total pressure ratio and mass flow rate. The study was performed and assessed for a low-aspect ratio turbine nozzle using 3D steady Reynolds-averaged N.S. solver. Using the knowledge of the flow physics analysis an optimized turbine nozzle was obtained.     

Experimental investigation of wake effects on wind turbine performance

The wake interference effect on the performance of a downstream wind turbine was investigated experimentally. Two similar model turbines with the same rotor diameter were used. The effects on the performance of the downstream turbine of the distance of separation between the turbines and the amount of power extracted from the upstream turbine were studied. The effects of these parameters on the total power output from the turbines were also estimated. The reduction in the maximum power coefficient of the downstream turbine is strongly dependent on the distance between the turbines and the operating condition of the upstream turbine. Depending on the distance of separation and blade pitch angle, the loss in power from the downstream turbine varies from about 20 to 46% compared to the power output from an unobstructed single turbine operating at its designed conditions. By operating the upstream turbine slightly outside this optimum setting or yawing the upstream turbine, the power output from the downstream turbine was significantly improved. This study shows that the total power output could be increased by installing an upstream turbine which extracts less power than the following turbines. By operating the upstream turbine in yawed condition, the gain in total power output from the two turbines could be increased by about 12%.     

Computational analysis of performance and flow investigation on wells turbine for wave energy conversion

Wells turbine is a self-rectifying airflow turbine capable of converting pneumatic power of the periodically reversing air stream in oscillating water column into mechanical energy. This paper reports the computational analysis on performance and aerodynamics of Wells turbine with the NACA 0021 constant chord blades. Studies have been made at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The present computational model can predict the performance and aerodynamics of the turbine quantitatively and qualitatively. The model also predicted the flow coefficient at which the turbine stalls, with reasonable accuracy.     

Computational and experimental study of pinch on the performance of a vaneless diffuser in a centrifugal compressor

This study focuses on the vaneless diffuser of a centrifugal compressor.The examined stage consists of an un-shrouded impeller,a parallel wall vaneless diffuser and a volute.The walls of the diffuser were movable allowingdifferent pinch configurations to be investigated.The baseline geometry had no pinch i.e.the height of the dif-fuser was equal to the height of the impeller flow channel plus the axial running clearance.The work consists ofboth numerical and experimental parts.Quasi-steady, turbulent,fully 3D numerical simulations were conducted.The inlet cone,rotor and diffuser were modelled.Six different configurations were studied.The height of thepinch was altered and the pinch made to different walls was tested.Two of the numerically studied cases werealso experimentally investigated.The overall performance of the compressor,the circumferential static and totalpressure and the spanwise total pressure distribution before and after the diffuser were measured.The numericaland experimental studies showed that the pinch improved the efficiency of the compressor.     

Comparison of pitching and plunging effects on the surface pressure variation of a wind turbine blade section

Numerous experiments were conducted on an oscillating airfoil in a subsonic wind tunnel. The experiments involved measuring the surface pressure distribution when the model oscillated in two types of motion, pitch and plunge, at three different Reynolds numbers, 0.42, 0.63 and 0.84 million, and over a range of reduced frequencies, k = 0.03–0.09. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphasis was placed on the effects of different types of motion on the unsteady pressure distribution of the airfoil at pre‐stall, near‐stall and post‐stall conditions. It was found that variations of the pressure distribution and aerodynamic loads with angle of attack were strongly sensitive to the displacement, oscillation frequency and mean angle of attack. The width of the hysteresis loop, position of the ‘figure‐8 shape’ and slope of the pressure coefficient curve are influenced by both types of motion, pitch and plunge. The main difference between plunging and pitching motions is due to the presence of the pitch rate for the pitching motion case, which was absent in the plunging case. Pitch rate had the strongest influence on pressure data in the near‐stall and post‐stall conditions. The trend of increasing the width of the hysteresis loops of lift coefficients with changing reduced frequency was different in two motions in the pre‐stall and post‐stall regions. The aerodynamic damping was greater for the pitching case than for the plunging one at higher reduced frequencies due to the existence of the pitch rate in the pitching oscillation, which was reversed at lower reduced frequencies. In the near‐stall region, at higher reduced frequency, the dynamic stall angle for the pitching oscillation increased while for the plunging one the effect was minimal. Increasing the oscillation amplitude was more effective for the plunging motion than for the pitching one. The effects of surface grit roughness on the pressure signature for both types of motion were also investigated. Applying the surface roughness near the leading edge affected the performance of the airfoil significantly. Copyright © 2008 John Wiley & Sons, Ltd.     

MS6001B重型燃机二级复环定位销的加工工艺

详细介绍了MS6001B重型燃机二级复环定位销孔现场定位和钻孔的工艺,以期提高复环安装的灵活性,并对GE公司制造的F6和F9重型燃机复环安装提供一般性指导.     

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.     

Aerodynamic Loading Distribution Effects on the Overall Performance of Ultra-High-Lift L Turbine Cascades简

The present paper reports the results of an experimental investigation aimed at comparing aerodynamic perform- ance of three low-pressure turbine cascades for several Reynolds numbers under steady and unsteady inflows. This study is focused on finding design criteria useful to reduce both profile and secondary losses in the aero-engine LP turbine for the different flight conditions. The baseline blade cascade, characterized by a standard aerodynamic loading （Zw=1.03）, has been compared with two Ultra-High-Lift profiles with the same Zweifel number （Zw=1.3 for both cascades）, but different velocity peak positions, leading to front and mid-loaded blade cascade configurations. The aerodynamic flow fields downstream of the cascades have been experimentally in- vestigated for Reynolds numbers in the range 70000〈Re〈300000, where lower and upper limits are typical of cruise and take-off/landing conditions, respectively. The effects induced by the incoming wakes at the reduced frequency ./＋=0.62 on both profile and secondary flow losses for the three different cascade designs have been studied. Total pressure and velocity distributions have been measured by means of a miniaturized 5-hole probe in a tangential plane downstream of the cascade for both inflow conditions. The analysis of the results allows the evaluation of the aerodynamic performance of the blade cascades in terms of profile and secondary losses and the understanding of the effects of loading distribution and Zweifel number on secondary flows. When operating un- der unsteady inflow, contrarily to the steady case, the mid-loaded cascade has been found to be characterized by the lowest profile and secondary losses, making it the most attractive solution for the design of blades working in real conditions where unsteady inflow effects are present.     

冷却流量对涂层叶片冷却性能影响的数值研究

采用气热耦合数值方法研究了冷却流量对热障涂层气冷涡轮叶片冷却性能的影响,并对结果进行了对比分析。研究结果表明：热障涂层叶片的综合冷却效率随冷却流量的增加而增大,但增幅则逐渐下降。在吸力面上,附加热障涂层的效果更好。基准工况下,附加热障涂层,叶片表面温度可降低72.6 K,综合冷却效率增幅最大可达6.5%。在尾缘区域,热障涂层会阻碍热量从金属叶片表面向低温的流体传递,导致叶片表面性能下降,因此,只有配合高效的内冷技术,才能达到理想的冷却效果。     

Investigation of the performance of a cross-flow turbine

An experimental investigation was conducted to study the effects of some geometric parameters of runners and nozzles (e.g., diameter ratio and throat width ratio) on the efficiency in the cross-flow turbines, by varying of ratio of inner-to-outer diameters of runners and gate openings of two different turbine nozzles under different heads. In this study, four different types of runners (170 mm outer diameter, 114 mm width) were designed and manufactured to investigate the effects of the ratio of inner-to-outer diameters of runners on the turbine efficiency. Each runner had 28 blades and the ratios of inner-to-outer diameters of runners were 0·75, 0·67, 0·58 and 0·54, respectively. The runners were denoted with the numbers 1, 2, 3 and 4, and nozzles A and B. The blade inlet and outlet angles were selected as 30° and 90°. Nozzles A and B were of rectangular cross-sectional channels. Nozzles outlet angles of two solid walls of 16° were measured from the circumferential direction. The performance parameters namely output power, efficiency, runaway speed, reduced speed and power for different nozzle/runner combinations were investigated by changing head range from 8 to 30 m, the nozzle A-runner combinations (A–1, 2, 3, 4) and from 4 to 17 m, the nozzle B-runner combination (B–2) at different gate openings. The results of the present study clearly indicated that there was a negligible difference (e.g., 3% in total between 0·54 and 0·75 diameter ratio) in the efficiency of turbine for different diameter ratios and heads, and that the highest efficiency was obtained as 72% for A–2. © 1998 John Wiley & Sons, Ltd.     

1.5MW风力机塔架-基础的动力特性研究

采用多种计算模型结合敏感性分析,研究了塔架及塔架-基础的动力特性,发现塔架与基础的振动有一定的耦合作用;考虑基础与塔架相互作用后,塔架各阶自振频率降低,特别是高阶自振频率降低较多;在地震液化等极端工况下,地基基础对塔架动力特性的影响更明显。总结并分析了塔架的振源,指出脉动风荷载是风力机设计中必须重视的部分;风绕塔架流动一般处于超临界或跨临界范围,在超临界范围不会出现明显的塔架涡激振动,在跨临界范围可能出现严重的振动;风轮属细长弹性体、气动特征明显,其振动响应比较复杂且易发生破坏事故。为减小柔性塔架振幅,给出了风力机起动时快速跳过瞬态共振区、增加塔架阻尼和优化塔架体型以进一步改善塔架动力特性等方面的建议。     

The effects of geometric parameters on the thermal performance of a rectangular natural circulation loop containing PCM suspensions

ABSTRACT

A numerical study that uses the finite difference method to model the fluid flow and heat transfer of a rectangular natural circulation loop that contains phase change material (PCM) suspensions is presented to investigate how geometric parameters affect the thermal performance. Parametric simulations were performed using different geometrical parameters in the following ranges: the dimensionless length of the heated section = 0.4–1; the relative elevation of the cooled section compared with the heated section = 0.5–2; and the aspect ratio of the loop = 0.25–1. The results determine the important geometric parameters that affect the heat transfer performance of the loop with the PCM suspension. In several of the geometric configurations, the heat transfer performance of the loop is significantly affected by the latent heat contribution associated with the melting/freezing of the PCM particles.