Effect of Diffusively Shaped Holes on the Turbulent Flow Field of a Film Cooling Plate

The gas turbine blades with diffusion film cooling holes are newlydeveloped blade struc- tures in the hydrogen combustion gas turbine,which has an extremely high inlet gas temperature (1700 deg. C). TheFluid Machinery Laboratory of Nagoya Institute o Technology conductedfirstly a new research o the turbulent flow field over the gasturbine blade with diffusion film cooling holes in Japan. Normal-typeand X-ray hot wires were applied in the measurement of the flowfield.

Study of Turbulent Flow of Film Cooling Holes with Lateral Expanded Exits

Hot wire measurements and flow visualization are presented for studying the turbulent flow field over a flat gas turbine film cooling blade with lateral expanded holes. Three mass flux ratios of jet to free stream, M = 0.5, 0.89, 1.5, are tested. The streamwise velocity, the turbulent intensities and the Reynolds shear stress are measured. The effect of the lateral expanded holes on the improvement of the turbulent flow field for film cooling of gas turbines can be analyzed from the measured spatial di...

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

A flat plate film cooling flow from a multi-exit hole configuration has been numerically simulated using both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) Computational Fluid Dynamics (CFD) formulations. This multi-exit hole concept, the Anti-Vortex Hole (AVH), has been developed and studied by previous research groups and shown to mitigate or counter the vorticity generated by conventional holes resulting in a more attached film cooling layer and higher film cooling effectiveness. The film cooling jets interaction with the free stream flow is a long studied area in gas turbine heat transfer. The present study numerically simulates the jet interaction with the multi-exit hole concept at a high blowing ratio (M = 2.0) and density ratio (DR = 2.0) in order to provide a more detailed, graphical explanation of the improvement in film cooling effectiveness. This paper presents a numerical study of the flow visualization of the interaction of film cooling jets with a subsonic crossflow. The contour plots of adiabatic cooling effectiveness were used to compare the multi-exit hole and conventional single hole configurations. The vortex structures in the flow were analyzed by URANS formulations and the effect of these vortices on the cooling effectiveness was investigated together with the coolant jet lift-off predictions. Quasi-Instantaneous Temperature Isosurface plots are used in the investigations of the effect of turbulence intensity on the cooling effectiveness and coolant jet coverage. The effect of varying turbulence intensity was investigated when analyzing the jets’ interaction with the cross flow and the corresponding temperatures at the wall. The results show that as the turbulence intensity is increased, the cooling flow will stay more attached to the wall and have more pronounced lateral spreading far downstream of the cooling holes.

EXPERIMENTAL STUDY OF FLOW FIELDS IN THE VICINITY OF A FILM COOLING HOLE EXIT

For the first time, an important ingested flow phenomenon was discovered inexperiments at the film cooling hole exit. The trends of 3-D flow fie1ds and the fullnessfactor, Ci, were discussed in detail over a wide range of now parameters and the geometryof fan-shaped holes at this exit plane. It has been confirmed that the main reason of creat-ing longitudinal bound vortices is not the flow iri the hole but the mixing of mainstreamand jet at its exit.

Computational Film Cooling Effectiveness of Dual Trench Configuration on Flat Plate at Moderate Blowing Ratios

In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with dual trench. Dual-trench confguradon consists of two trenches together, one wider trench and the other is narrow trench that extruded from the wider one. Several blowing ratios in the range （0.5：5） were investigated. The pitch-to-diameter ratio of 2.775 is used. By using the dual trench configuration, the coolant jet impacted the trench wall two times allowing increasing the spreading of coolant laterally in the trench, reducing jet velocity and jet completely covered on the surface. The results indicate that this configuration increased adiabatic effectiveness as blowing ratio increased. The spatially averaged adiabatic effectiveness reached 57.6% for at M= 2. No observed film blow-off at all blowing ratios. The adiabatic film effectiveness of dual trench case outperformed the narrow trench case, laidback fan-shaped hole, fan-shaped hole and cylinder hole at different blowing ratios.

Analysis of Film Cooling Effectiveness on Shaped Hole and Antivortex Hole

Film cooling is introduction of a secondary fluid （coolant or injected fluid） at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.

Novel Shaped Sweeping Jet for Improved Film Cooling and Anti-Deposition Performance

The present study proposed a shaped sweeping jet(SJ)that possesses the merits of both SJ and shaped hole,which demonstrates significantly improved cooling effectiveness and anti-deposition performance.Compared to a classical 777 shaped hole,the shaped SJ exhibits a maximum enhancement of 70%in cooling effectiveness and a maximum reduction of 28%in particle deposition height,respectively.Owing to the periodic oscillation of coolant jet and higher streamwise jet momentum,the shaped SJ can provide much wider coolant coverage and therefore sweep the adhesive particle away from the wall.This study is the first attempt to reconcile the performance of film cooling and particle anti-deposition simultaneously,which offers a promising design concept for future engine cooling.

Numerical Prediction of Film Cooling Effectiveness over Flat Plate using Variable Turbulent Prandtl Number Closures

Numerical simulations were performed to predict the film cooling effectiveness on the fiat plate with a three- dimensienal discrete-hole film cooling arrangement. The effects of basic geometrical characteristics of the holes, i.e diameter D, length L and pitch S/D were studied. Different turbulent heat transfer models based on constant and variable turbulent Prandtl number approaches were considered. The variability of the turbulent Prandtl number Prt in the energy equation was assumed using an algebraic relation proposed by Kays and Crawford, or employing the Abe, Kondoh and Nagano eddy heat diffusivity closure with two differential transport equations for the temperature variance ko and its destruction rate εθ The obtained numerical results were directly compared with the data that came from an experiment based on Transient Liquid Crystal methodology. All implemented models for turbulent heat transfer performed sufficiently well for the considered case. It was confirmed, however, that the two- equation closure can give a detailed look into film cooling problems without using any time-consuming and inherently unsteady models.

基于物理信息神经网络的气膜冷却湍流模型反演学习

由于气膜冷却问题中湍流的复杂特性,传统雷诺平均(RANS)方法会低估湍流的热扩散强度,导致冷却效果计算不准确。对此提出了一套基于物理信息神经网络(PINN)的湍流建模框架,基于RANS流场和大涡模拟(LES)温度场,建立了数据驱动的湍流普朗特数神经网络模型,在RANS求解器中嵌入该模型,可以动态调整湍流的热扩散强度,获得了与LES高度一致的温度场。结果表明:PINN是构建数据驱动湍流模型的良好方法,对于湍流普朗特数的建模可以有效提升RANS方法对温度预测的准确性。

延伸冲击-扇形气膜孔复合结构耦合换热实验与数值研究

针对冲击-气膜复合冷却结构,采用实验与数值方法,对比了基于圆形气膜孔的传统冲击、延伸冲击、小距离冲击、基于扇形气膜孔的传统冲击、延伸冲击5种复合冷却系统的耦合换热和流动特性。采用红外热成像技术,获得了5种复合冷却结构在吹风比分别为0.6、1.0、1.5时外壁面的综合冷却有效度,并通过数值计算进一步揭示了内部冷却的流动和换热特征。研究结果表明:在不产生额外气动损失的前提下,延伸冲击孔结构可提升内部冷却的换热系数,进而小幅度提升壁面的综合冷却有效度,幅度为1.2%~4.6%,但随着冷气量的增大综合冷却有效度提升幅度有所减小;减小冲击距离能够提升内部冲击换热效果,但不会对综合冷却有效度产生明显影响;采用扇形气膜孔可大幅度提升外部气膜冷却性能,且提升幅度大于采用延伸冲击内部改进结构的。相较于传统的圆形气膜孔-冲击复合冷却结构,在相同冷气量条件下,基于扇形孔的延伸冲击改进方案可将壁面的面平均综合冷却有效度提高7.6%~8.5%,并将系统的流量系数提升30%以上。

燃烧室百叶与双排孔冷气对透平端壁冷却性能影响研究

针对燃烧室与透平冷气掺混导致实际二次流发展及端壁冷却性能偏离设计值的问题,综合考虑燃烧室百叶冷气尾迹与双排孔射流,数值研究了多源冷气射流在燃烧室与透平交界区的掺混机制,分析了其对透平静叶端壁气膜冷却与流动特性的影响规律。研究结果表明:空腔涡卷吸大部分百叶冷气,并跨越双排孔冷气向下游发展,马蹄涡卷吸限制大部分双排孔冷气,并向空腔涡外侧发展;当双排孔冷气吹风比M_h=0.5,1.0较小时,马蹄涡导致冷气形成楔形高冷效区域,空腔涡的附着侧和分离侧分别产生了高、低冷效区,随着百叶冷气吹风比M_l的增加,空腔涡强度显著降低,导致位于楔形中心的分离侧冷却效率有所提升;当双排孔冷气吹风比M_h为1.5时,双排孔冷气部分跨越马蹄涡,静叶端壁可实现完全冷气覆盖,此时百叶冷气吹风比M_l从0.5增加到1.5,静叶端壁平均冷却效率可从0.4提升到0.63。该研究为考虑燃烧室与透平交界区实际流动掺混情况的静叶端壁冷却结构与布局设计提供理论基础。

冷气流量比对三维涡轮导叶全气膜冷却效率的影响

为了研究不同主流湍流度下冷气质量流量比对三维涡轮导叶全气膜冷却特性的影响,使用热色液晶测量了在主流湍流度为1%和15%,流量比为5.5%、8.4%和12.5%下三维涡轮导叶的全气膜冷却效率分布。结果表明:在不同的叶片区域和主流湍流度下,流量比对气膜冷却特性的影响规律也有所不同;在低主流湍流度下,冷却效率整体上随着流量比的增大而升高,但是在叶片的叶尖和吸力面中截面区域冷却效率在大流量比下降低,且叶片吸力面中弦区域的冷气呈波纹状分布;高主流湍流度使冷气射流与主流之间的掺混更加剧烈,可以抑制吸力面的冷气脱离壁面且使其分布更加均匀,冷却效率随流量比增大而升高。

Experimental Investigation on the Effect of Mainstream Turbulence on Full Coverage Film Cooling Effectiveness for a Turbine Guide Vane

Experiments have been performed to investigate the effect of mainstream turbulence on the three-dimensional distribution of the full coverage film cooling effectiveness for two enlarged actual twisted vanes with cylindrical or shaped holes. The film cooling effectiveness was measured by transient liquid crystal technique at mainstream turbulence intensities of 2%, 9% and 15%. The mass flow rate ratios range from 5.5% to 12.5%. There are 3, 8 and 7 rows of film holes on the suction side, leading edge and pressure side, respectively. Results show that for the cylindrical hole vane the high mainstream turbulence intensity decreases the film cooling effectiveness in the top region and down region of pressure side in the low mass flow rate ratio of 5.5%, while the effect is opposite in the high mass flow rate ratio of 12.5%. The film cooling effectiveness in the middle region of pressure side decreases obviously with the increase of the turbulence at the low mass flow rate ratio of 5.5%, while the influence of increasing turbulence weakens gradually with the increase of mass flow rate ratio. Moreover, the high mainstream turbulence improves the film cooling effectiveness in the further downstream of the holes on suction side at the high mass flow rate ratio of 12.5%. For the shaped hole vane, the increase of mainstream turbulence decreases the film cooling effectiveness at all mass flow rate ratios. This study reveals the influence rule of the mainstream turbulence on the film cooling effectiveness in the different regions of the three-dimensional vane surface. The results would guide the designs of engineering heat transfer with application in gas turbine blade/vane cooling.

Pressure performance for a thin-walled ring and turbulent-jet orifice modeled elastic squeeze film damper

This paper explores an analytical model for Elastic Ring Squeeze Film Damper(ERSFD) with thin-walled ring and turbulent-jet orifices, and uncovers its Oil Film Pressure Performance(OFPP). Firstly, the ring deformation is addressed by using the Fourier series expansion approach and the orifice outflow rate is characterized with the Prandtl boundary layer theory. Secondly, applying finite difference scheme, the influence of elastic ring flexibility, orifice diameter, and attitude angle on the OFPP is analyzed. Finally, Outer chamber pressure was measured experimentally at different rotor speeds. The results indicate that the outer chamber pressure coats an individual load-carrying region and spreads symmetrically pertaining to the attitude angle. Its amplitude drops as the elastic ring flexibility decreases but boosts with the reduction of the orifice diameter.For inner chamber pressure, the orifice diameter effects a similar trend to the outer cavity, but exhibits more stable distribution regarding the attitude angle. Minimizing the elastic ring flexibility causes an increase in amplitude. The model is validated by the test results giving that the outer chamber pressure shifts synchronously and periodically with the variation of the attitude angle,while the pressure amplitude increases slightly at higher rotor speeds.

Influence of Turbulators in Blade Cooling Passages on Film Hole Discharge Coefficients

This paper details the results of a joint project between Rolls-Royce Deutschland (RRD) and the Northwestern Polytechnical University of China (NWPU). The objective of the project was the determination of the influence of tabulators in turbine blade cooling passages on film hole discharge coefficients (Cd coefficients). A large-scale plexiglas model was used by the NWPU to measure the turbulator influence on Cd coefficients for a wide range of different geometrical parameters, Reynolds numbers and cooling flow off take ratios. RRD specified the comprehensive test matrix and analysed the test data. The CFD code FLUENT was used by RRD for numerical simulation of the test cases with the main objective to support the interpretation of observed trends. Both, experimental and numerical results will be presented in this paper for a selection of test configurations.

Assessment of the Turbulence Characteristics of Shaped Film Cooling Hole with Scale Resolving Simulation

The turbulence characteristics of the shaped hole film cooling are very complex.In this study,Large Eddy Simulation(LES)and Reynolds-averaged Navier-Stokes(RANS)are used to study the film cooling of the shaped hole.The time-averaged results are compared with the experimental data in the literature.Because of the eddy-viscosity model,the RANS method roughly deals with the simulation of boundary layer,which leads to a large deviation.The RANS results are compared with the LES results to identify the weaknesses of the Realizable k-e model in predicting the turbulence characteristics of the shaped hole film cooling.The eddy viscosity hypothesis and the temperature gradient diffusion hypothesis are evaluated using LES data.Furthermore,the turbulence characteristics of the in-hole flow are analysed with the help of the incremental Proper Orthogonal Decomposition(iPOD).The turbulence presents strong anisotropy and some convection structures are induced from the shear zone.

Computational research on film cooling under rotating frame by an anisotropic turbulence model

A new anisotropic k-o turbulence model was proposed in this paper.This new model,with the standard k-o model and the standard k-e model was embedded in our three-dimensional(3-D)Navier-Stokes code to compute rotational film cooling.In addition,the theoretical and numerical analysis on the influence of the Coriolis and buoyancy forces induced by the rotation was discussed in detail.Major findings of this study are as follows:⑴The new anisotropic k-o model preformed much better compared to its isotropic counterparts.(2)In the region of 6D-12D downstream the film hole,the numerical results of the new model were much closer to the experimental data than that in the region of 0-6D.(3)The constant density term can be balanced by the pressure gradient and would not influence the velocity and temperature distributions.But the centrifugal buoyancy force and the Coriolis force would change the trajectory of cooling air and temperature distributions.

Laws of Jet Mixing of the Swirled Flows in a Pipe

Results of experimental research of the mixing process of coaxial flows in a pipe with swirled peripheral jet are presented in this paper. Distribution of temperature and concentration of gases on the axis and wall of the channel under the influence of such factors as the regime flow, ratio of density of flows and swirl degree of the peripheral jet are studied. Research of temperature, swirl angle, circulation in cross sections along with the channel have shown that their distributions have the jet-like character and are described by known dependences for the layer of mixture.

薄环-紊动射流小孔挤压油膜阻尼器压力特性

为研究单层弹性环式挤压油膜阻尼器(elastic ring squeeze film damper,ERSFD)的油膜压力特性,建立薄环-紊动射流小孔模型。通过平面薄环弯曲理论和普朗特边界层理论分别计算弹性环变形和阻尼孔出口净流速;分析弹性环柔度、阻尼孔直径及进动角变化对油膜压力特性的影响,并开展外腔油膜压力多转速测量试验。结果表明:外腔油膜压力随弹性环柔度的减小而下降,但随阻尼孔直径的减小而增加;对于内腔油膜压力,阻尼孔直径的影响与外腔相似,但减小弹性环柔度导致压力增加。试验表明,外腔油膜压力在不同转速下均同步方位角周期变化,而高转速时,压力幅值略有增加。