A numerical investigation of new film cooling hole configuration at the leading edge of asymmetrical turbine blade: part A

The focus of the first part of this numerical study is to investigate the effects of two new configurations: (1) slot with cylindrical end and (2) slot with median cylindrical hole, generated by the combination between two film cooling configurations: cylindrical hole and uniform slot. Computational results are presented for a row of coolant injection holes on each side of an asymmetrical turbine blade model near the leading edge. For each configuration, three values of the radius are taken: R = 0.4, R = 0.8 and R = 1.2. The six cases simulations, thus obtained, are conducted for the same density ratio of 1.0 and the same inlet plenum pressure. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. Results show that, at the pressure side; for the two new configurations, the six studied cases exceed the case baseline in cooling effectiveness term with the best result obtained for R = 0.8 (case 2). For the suction side, only configurations with R = 0.4 (cases 1 and 4) provide an increase of film effectiveness compared to the case baseline. The following configuration: Cases 1 or 4 at the suction side and case 2 at the pressure side, gets the best thermal protection because of their higher coverage and strong cooling effectiveness.     

Numerical investigation of the influence of incidence angle on asymmetrical turbine blade model showerhead film cooling effectiveness

The influence of various incidence angles on film cooling effectiveness of an axial turbine blade cascade with leading edge ejection from two rows of cooling holes is numerically investigated. The rows are located in the vicinity of the stagnation line. One row is located on the suction side and the other one is on the pressure side. The predicted pressure field for various blowing ratios (M = 0.7, 1.1 and 1.5) is compared with available experimental results at the design condition. Moreover, the effect of various incidence angles (?10°, ?5°, 0°, 5° and 10°) at three blowing rates is investigated by analyzing the results of both laterally averaged and area averaged values of adiabatic film cooling effectiveness. Numerical results indicate that the incidence angle can strongly affect the thermal protection of the blade at low blowing ratio but becomes less dominant at high blowing ratio. In fact, for the low blowing ratio, a small change in the incidence angle that relates to the design condition can deeply affect the thermal protection of the blade, which is evident from the laterally and area averaged film cooling effectiveness distributions.     

Experimental study of the effects of spanwise rotation on the flow in a low aspect ratio diffuser for turbomachinery applications

Two dimensional time accurate PIV measurements of the flow between pressure and suction side at different spanwise positions of a rotating channel are presented. The Reynolds and Rotation numbers are representative for the flow in radial impellers of micro gas turbines. Superposition of the 2D results at the different spanwise positions provides a quasi-3D view of the flow and illustrates the impact of Coriolis forces on the 3D flow structure. It is shown that the inlet flow is little affected by rotation. An increasing/decreasing boundary layer thickness is reported on the suction/pressure side wall halfway between the channel inlet and outlet. The turbulence intensity moves away from the suction side wall and remains close to the pressure side wall. The instantaneous measurements at mid-height of the rotating channel reveal the presence of hairpin vortices in the pressure side boundary layer and symmetric vortices near the suction side. Hairpin vortices occur in rotation in the pressure and in the suction side, for the measurement plane close to the channel bottom wall.     

An Experimental Study of the Rotational Effects on Separated Turbulent Flow During Stall Delay

Three-dimensional velocity fields were measured using tomographic particle image velocimetry (Tomo-PIV) on a model of the blade of a small-scale horizontal axis wind turbine (HAWT) to study the effects of rotation on separated turbulent flows during stall delay at a global tip speed ratio (TSR) of 3 and a Reynolds number of 4800. The flow fields on a static airfoil were also measured at a similar angle-of-attack (AOA) and Reynolds number for comparison. It was observed that the blade’s rotation in the streamwise direction significantly affected both the mean flow and the turbulence statistics over the suction surface. The mean velocity fields revealed that, different from the airfoil flow at large AOA, the recirculation region with reversed flow did not exist on the suction surface of the blade and the flow was rather attached. Mean spanwise flow from blade’s root to its tip was also generated by the rotation. The mean vorticity vector of the blade flow was found to be tilted in the rotational direction of the blade, as well as in the wall-normal direction. Of particular effects of the rotation on Reynolds stresses were the enhancement of 〈w ²〉 and the creation of strong 〈v w〉. The production of Reynolds stresses was also affected by blade’s rotation directly through the rotational production terms and indirectly by dramatically changing the fluctuating velocity fields. The distribution of enstrophy was observed to be modified by rotation, too.     

高速涡轮泵机械密封端面温度变化规律研究

以高速涡轮泵用机械密封为研究对象,以15#液压油为试验介质,考虑循环冷却量、转速、介质压力以及不同摩擦副配对等因素,采用自行搭建的高速密封试验台开展端面温度变化规律的研究. 结果表明:对于高速机械密封,上述因素均对端面温度产生影响,其中转速对端面温度的影响基本成线性关系,循环冷却量对端面温度的影响存在一个阈值,建议实际设计时取阈值的120%,介质压力对端面温度产生影响较大,但是影响程度不如转速;以尽可能获得低的端面温度值来判断,用作静环时浸渍树脂石墨比普通石墨合适,用作动环时碳化硅比钼合金合适.      

Rapid diagnosis of flow separation around an axial impeller in a mixing vessel

 The relative flows around a flat plate axial impeller in a mixing vessel were visualized directly using a combined image shifting and image de-rotation technique. The image shifting technique used a rotating mirror to produce a velocity bias equal to the blade velocity so that the relative flow field could be studied in a co-axial plane cutting through the 2-dimensional blade section. The technique provides a rapid means of locating local flow separation on the blade. To visualize the relative flow field in the plane of the blade span, an image de-rotation method was used. The method includes using a dove-shaped prism which, when rotated, produce a rotation of an image about the optical axis. It was observed in the relative frame of reference through the prism that a new vortex structure, not reported previously, with vorticity sign opposite to that of the rotation of the shaft, exists near the hub at the high pressure side of the blade. Received: 17 June 1996/Accepted:12 November 1996     

干气密封旋转流场的宏观特性与介观速度场的逻辑关系研究

旋转流场中的流体流动比较复杂,特别是在高转速、微尺度工况时,流场中的流体流态及其判断方法缺乏完备的理论模型. 选择干气密封作为高速旋转流场的研究对象,以开启力和泄漏量作为宏观特性表征指标参数,选择剪切(周向)、径向及轴向速度分量对速度流场进行介观表述,通过Fluent软件仿真计算大跨距转速(低转速至超高转速)时的宏观、介观指标参数,研究密封性能指标参数与速度场间的内在逻辑关系. 结果表明:低速旋转流场中的轴向速度分量较小,可忽略不计,转速升高会促使轴向速度分量持续增大,当转速持续增大并超过某一临界值时,轴向速度分量会出现迅速升高的情形;轴向速度分量的变化情形与微尺度流场(开启力和泄漏量)波动密切相关,是影响旋转流场流态的关键性指标参数,也是引起宏观流场特性变化的主要因素;径向速度分量的变化情形与微尺度流场泄漏量的变化规律基本一致,随着转速的增大,泄漏量的宏观性能反馈要早于开启力波动的出现. 基于以上研究,同时根据管道雷诺数、流量因子判定模型及流体力学基本理论,尝试提出了基于三维速度分量的针对旋转流场流态的椭球判定模型.      

双通道旋转输流管临界流速和振动模态分析

旋转叶片是航空发动机重要零件之一,服役条件十分恶劣,常常因振动过量导致其失效.为了合理设计含冷却通道的叶片,保证其可靠性与安全性,需对含冷却通道的叶片的振动特性进行研究.基于EulerBernoulli梁理论,将叶片简化为含两通道的悬臂旋转输流管,考虑了通道轴线偏移量对流体动能的影响,采用Lagrange原理结合假设模态法建立包含双陀螺效应的运动控制方程,采用降阶扩维的方法求解系统特征值.研究两通道模型的流速比、转速和长细比等对前3阶特征根曲线影响.将文章模型退化为简支单通道输流管,与文献报道结果进行对比,部分验证建模方法的正确性.研究发现:在相同的管道截面积下,两通道模型的临界流速值大于单通道模型的;旋转运动引入的陀螺效应会使得第2, 3阶特征根轨迹发生绕圈现象,并多次穿越虚轴;随着长细比的增大,系统会表现出类似非旋转的悬臂输流管的动力学行为;系统的横向位移模态响应呈现出行波特性,且在不同参数组合下,阻尼因子对前3阶模态产生不同的增强或减弱作用.     

Predicting Noninertial Effects with Linear and Nonlinear Eddy-Viscosity, and Algebraic Stress Models

Three types of turbulence models which account for rotational effects in noninertial frames of reference are evaluated for the case of incompressible, fully developed rotating turbulent channel flow. The different types of models are a Coroiolis-modified eddy-viscosity model, a realizable nonlinear eddy-viscosity model, and an algebraic stress model which accounts for dissipation rate anisotropies. A direct numerical simulation of a rotating channel flow is used for the validation of the turbulence models. This simulation differs from previous studies in that significantly higher rotation numbers are investigated. Flows at these higher rotation numbers are characterized by a relaminarization on the cyclonic or suction side of the channel, and a linear velocity profile on the anticyclonic or pressure side of the channel. The predictive performance of the three types of models are examined in detail, and formulation deficiencies are identified which cause poor predictive performance for some of the models. Criteria are identified which allow for accurate prediction of such flows by algebraic stress models and their corresponding Reynolds stress formulations.     

Visualization study of the flow in and around a Savonius rotor

Flow in and around a Savonius rotor has been studied by flow visualization experiments, and the rotation effect is discussed in comparison with the measured pressure distributions on the blade surfaces. It is observed that the flow separating regions on the blade surfaces are fairly reduced by the rotation effect and the flow through the overlap is weakened by the appearance of resisting flow. The former contributes to the torque production of the rotating rotor while the latter acts as a resistance. These phenomena together with the stagnation effect on the front side of the rotor contribute to the power producing mechanism of the Savonius rotor.     

Film cooling effectiveness from trenched shaped and compound holes

This paper presents a comparative-numerical investigation on film cooling from a row of simple and compound-angle holes injected at 35° on a flat plate with four film cooling configurations: (1) cylindrical film hole; (2) 15° forward diffused film hole; (3) trenched cylindrical film hole; (4) trenched 15° forward-diffused film hole. All simulations are at fixed density ratio of 1.6, blowing ratio of 1.25, length-to-diameter L/D = 4 and pitch-to-diameter ratio of 3.0. The effect of length-to-diameter ratio on film cooling has been also investigated using L/D in the range of 1–8. Computational solutions of the steady, Reynolds-averaged Navier–Stokes equations have been obtained using a finite volume method. It has been found that the shape of the hole and the trenched holes can significantly affect the film cooling flow over the protected surface. Further, it has been shown that the film cooling effectiveness by trenched shaped holes is higher than all other configurations both in spanwise and streamwise specially downstream of the injection. Also, a trenched compound angle injection shaped hole produces much higher film cooling protection than the other configurations investigated in the present paper. The length-to-diameter ratio of trenched holes was found to have a significant effect on film cooling effectiveness and the spread of the coolant jets.     

Shroud heat transfer measurements inside a heated multiple rotating cavity with axial throughflow

Experimental measurements of heat transfer are made from the inner peripheral surface of a rotating test rig designed to be similar to a gas turbine high pressure compressor internal air system. The test rig comprises a number of annular discs sealed at their periphery by a shroud. An axial throughflow of cooling air enters the test rig and flows through the annular section between the disc bores and a central shaft. Tests were carried out for the following range of rotational speeds and axial throughflow rates: 540 < N_R < 10,800 rev/min and (corresponding to the range of rotational and axial Reynolds numbers 4 × 10⁵ < Re < 7.7 × 10⁶ and 3.3 × 10⁴ < Re_z < 2.2 × 10⁵).

The shroud Nusselt numbers are found to depend on the shroud Grashof number. They are relatively insensitive to changes in axial Reynolds number and two geometrically similar cavities give similar values of Nusselt number. The heat transfer from the shroud is governed by the mechanism of free convection. It is recommended that a modified form of a correlation for Rayleigh–Bénard convection in a gravitational force field be used, with appropriate modification, to predict shroud heat transfer.     

Two-equation turbulence models for prediction of heat transfer on a transonic turbine blade

Two versions of the two-equation k–ω model and a shear stress transport (SST) model are used in a three-dimensional, multi-block, Navier–Stokes code to compare the detailed heat transfer measurements on a transonic turbine blade. It is found that the SST model resolves the passage vortex better on the suction side of the blade, thus yielding a better comparison with the experimental data than either of the k–ω models. However, the comparison is still deficient on the suction side of the blade. Use of the SST model does require the computation of distance from a wall, which for a multi-block grid, such as in the present case, can be complicated. However, a relatively easy fix for this problem was devised. Also addressed are issues such as (1) computation of the production term in the turbulence equations for aerodynamic applications, and (2) the relation between the computational and experimental values for the turbulence length scale, and its influence on the passage vortex on the suction side of the turbine blade.     

垂直旋转流场中单颗粒运动状态判别及受力分析

为研究单颗粒在旋转流场中的运动状态及受力情况,以毫米级球形颗粒为例,利用旋转流场颗粒运动装置,通过使用摄像机记录颗粒在流场中的运动轨迹以获取其运动参数,分析了不同转速和颗粒直径条件下颗粒的运动轨迹,拟合得到了颗粒运动状态判别公式以及颗粒运动轨迹公式,分析了颗粒在旋转流场中的受力情况。结果表明,颗粒在旋转流场平衡状态下运动状态主要分为两类,一类是未离开壁面保持静止,另一类是离开壁面保持稳定周向运动;颗粒进行周向运动的轨迹为椭圆形,并且圆心随着转速的增大靠近旋转中心,而随着粒径的增大靠近壁面;颗粒在旋转流场的运动过程中主要受到离心力和旋转科式力作用。     

Heat transfer study in rotating cascade using IR thermography and CFD analyses

This paper presents an experimental and CFD numerical study of convective heat transfer in a rotating cascade. Infrared thermography was used to measure surface temperature distribution on a rotating hollow blade, heated internally by secondary air. A CFD numerical model was made according to the actual test rig geometry and operating conditions. Tests were carried out in an iposonic flow regime at relatively low fluid temperatures, with the rotational and Reynolds numbers varied and hot-to-cool air mass flow ratio kept constant. Experimental and numerical results for the blade pressure side are compared in terms of surface temperature 2D distribution and Nusselt number one-dimensional distribution along the blade midspan, providing a reasonable agreement.     

离心惯性力效应对超临界二氧化碳干气密封流场与密封特性影响分析

为揭示离心惯性力效应对S-CO₂干气密封流场与密封特性的影响规律,以螺旋槽干气密封为研究对象,引用考虑离心惯性力效应的Reynolds方程,在考虑气膜真实气体效应、黏度随压力与温度双重变化的同时,基于N-S方程与能量守恒定律,建立了绝热状态下考虑离心惯性力效应作用的能量控制方程. 然后,采用有限差分法对压力控制方程与能量控制方程进行耦合求解,并对考虑离心惯性力效应与没有考虑离心惯性力效应下的压力分布、温度分布以及密封特性进行了分析讨论. 研究表明:离心惯性力效应具有削弱流场内压力与温度的作用;从避免凝结流动角度考虑,离心惯性力效应引起的温降将不利于S-CO₂干气密封;考虑离心惯性力效应作用时,气膜开启力在不同槽深与转速下存在最佳工况点,泄漏率随着转速的增加显著减小,而离心惯性力效应与膜厚之间没有强交互作用;考虑离心惯性力效应作用的气膜开启力、泄漏率、出口温度均比不考虑离心惯性力效应作用的小,且这种差异随着转速的增大而增加,而随着膜厚的变化没有改变. 这些结果为进一步研究S-CO₂干气密封奠定了一定的理论基础.      

Numerical simulation of the effect of plasma aerodynamic actuation on improving film hole cooling performance

The primary goal of this paper is to study film cooling performance for a cylindrical hole with plasma aerodynamic actuation. The simulation model of plasma aerodynamic actuation on improving film hole cooling effectiveness was established. The heat effect of plasma aerodynamic actuation model was taken into consideration. It was firstly found that the velocity and blowing ratio greatly affect the film cooling effectiveness. Then, position, power input, and the number of plasma actuators were particularly investigated.     

Non-uniform mass transfer or wall enthalpy into a compressible flow over a rotating sphere

A study for the effect of non-uniform slot injection/suction and non-uniform total enthalpy at the wall for a steady non-similar laminar compressible boundary layer flow over a rotating sphere is presented. The effects of rotation and free stream Mach number have also been considered. Non-similar solutions have been obtained from the starting point of the stream wise coordinate to the point of separation using an implicit finite difference scheme in combination with the quasi-linearization technique. The results indicate that the separation can be delayed by non-uniform slot suction and also by moving the slot downstream but the non-uniform slot injection has just the opposite effect. An increase of rotation and total enthalpy at the wall causes separation to occur earlier while cooling delays it. An increase of the Mach number shifts the point of separation upstream due to the adverse pressure gradient. The non-uniform total enthalpy at the wall has a very little effect on the skin friction and hence on the point of separation.     

Numerical study on film cooling effectiveness from shaped and crescent holes

This paper presents a comparative numerical investigation on film cooling from a row of holes injected at 35° on a flat plate with three film cooling configurations, including cylindrical hole, 15° forward diffused shaped hole, and new crescent hole. All simulations are conducted at blowing ratio of 0.6 and 1.25, length-to-diameter ratio of four and pitch-to-diameter ratio of three. Computational solutions of the steady, Reynolds averaged Navier–Stokes equations are obtained using a finite volume method. Previous successful application of a two-layer turbulence model to cylindrical hole is extended to predict film cooling for the different hole geometries. It has been found that the film cooling effectiveness of cylindrical holes obviously declined along with increasing the blowing ratio. While the forward diffused shaped hole presents a marked improvement, with a higher effectiveness at the lateral area between adjacent holes. By comparison, the crescent hole exhibits the highest film cooling effectiveness among the three configurations both in spanwise and streamwise especially downstream of the intersection of the two holes. Also, the crescent hole can restrain the vortex intensity, and then enhance the film cooling effectiveness.