变截面主流加速对超音速气膜冷却的影响

本文对扩张通道和直通道中的超音速气膜冷却进行了数值模拟,分析了主流加速和不加速两种情况下超音速气膜冷却的差异.计算结果表明,在主流加速的情况下,超音速气膜冷却的效果要好于相同进口条件下主流不加速的情况,并且这种差异越到下游越明显.同时,在本文计算的工况范围中,无论主流加速还是不加速,增大主流进口马赫数或者减少冷却流进口马赫数都使气膜冷却效率下降,而壁面静压则由主流气体决定.     

涡轮动叶吸力侧单排气膜孔冷却性能研究

本文通过数值模拟的方法,针对涡轮叶片吸力侧的单排气膜孔,研究了无量纲气膜孔出流位置、气膜孔复合角度和冷却空气质量流量占比对其气膜冷却效率与气动掺混损失的影响。结果表明,对于近前缘气膜孔,0.5%的冷却空气质量流量可以在保证较好的气动效率的同时在下游附近提供较高的绝热气膜冷却效率;对于中后部气膜孔,90°的气膜孔导致的掺混损失比相同冷气量的近前缘气膜孔高出一倍,此时复合角为60°的气膜孔有更好的气膜冷却效果。对比不同的孔排位置,位于流向位置0.3的气膜孔可以在下游较大区域取得良好的冷却效果,而且不引起过大的掺混损失。     

Efficiency of energy separation at compressible gas flow in a planar duct

The method of energy separation in a high-speed flow proposed by A.I. Leontyev is investigated numerically. The adiabatic compressible gas flow (of a helium-xenon mixture) with a low Prandtl number in a planar narrow duct and a flow with heat exchange in a duct partitioned by a heat-conducting wall are analysed. The temperature recovery factor on the adiabatic wall, degree of cooling the low-speed flow part, temperature efficiency, and the adiabatic efficiency in a duct with heat exchange are estimated. The data are obtained for the first time, which make it possible to compare the efficiency of energy separation in a high-speed flow with the efficiency of similar processes in vortex tubes and other setups of gas-dynamic energy separation.     

基于BP神经网络的多参数气膜冷却效率研究

气膜冷却作为当代燃机高温透平中必需的冷却手段,其冷却性能在多种参数的影响下表现复杂。采用BP神经网络模型对多种几何、流动参数变化下的气膜冷却系统的绝热气膜冷却效率进行预测。选择气膜冷却系统的吹风比、密度比、主流湍流度、面积比和长径比作为神经网络的输入参数,以燃气轮机透平叶片气膜冷却的实际运行工况为范围建立数据库。计算结果表明,采用贝叶斯归一化法训练后建立的气膜冷却神经网络模型在预测精度上要优于经验公式法,而且参数适用范围更广,具有良好的发展应用前景。     

Self-excited pressure pulsations in ethanol under heater subcooling

This paper presents experimental results of investigation of high-intensity cooling of high-temperature metal heater by subcooled ethanol flow. The experiments have proved the presence of self-excited pressure pulsations with amplitude of 1.15 MPa, arising in ethanol. Expanding real signals of the sensors by the Hilbert?Huang transform has resulted in the intrinsic mode functions. Analysis of these functions and the high-speed video shooting results allows identifying the basic frequencies and mechanisms of pressure oscillations. Comparison of the results with the data of film cooling and bubble boiling on the cooled heater has shown that maximum values of non-stationary heat-transfer coefficients for the self-excited oscillations and for the bubble boiling are the same.     

Wall shear stress around a stationary gas slug in a downward liquid flow

A single cell of the gas-liquid slug flow was studied. The flow around an immobile gas slug in a downflow of liquid and under its bottom was measured. The values of the wall shear stress and its pulsations were measured by the electrodiffusion method depending on a distance from the slug nose. It is shown that in a liquid film around a slug, turbulent pulsations are damped in comparison with a single-phase liquid flow. In the bottom part of a slug, where vortices are detached, turbulent pulsations exceed significantly the single-phase ones. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-08-00405a).     

Flat plate film cooling from a single-row inclined holes embedded in a trench: effect of external turbulence and flow acceleration

Results of an experimental study of a flat plate film cooling efficiency from a single row of inclined holes embedded in a “shallow” trench are presented. It is shown the cooling efficiency of such a configuration is much greater than that of the traditional configuration of inclined round holes. This provides more uniform surface coverage by the coolant film. The flow external turbulence increases the film cooling efficiency by 5–8%, while the freestream flow acceleration reduces it by 10–15%.     

不同主流进口湍流度下的超音速气膜冷却

本文通过数值模拟的方法计算并分析主流进口湍流度、冷却流进口高度和进口马赫数对超音速气膜冷却的影响。计算结果表明,主流进口湍流度对超音速气膜冷却有较大影响,增大主流进口湍流度会减弱超音速气膜冷却效率,同时还表明,增大冷却流进口高度以及进口马赫数,能减弱主流湍流度对超音速气膜冷却的影响。     

涡轮叶片端壁槽缝气与离散气膜孔冷却特性实验研究

真实发动机涡轮叶片端壁为曲面造型,并且其冷却受槽缝气、泄漏流和离散气膜冷却多种冷却气叠加影响,同时又受到主流二次流影响,因此呈现复杂冷却特性。为研究接近真实发动机涡轮叶片端壁构型和工况下的气膜冷却特性,本文采用高速风洞(主流雷诺数为37万)及压敏漆(PSP)技术,研究了槽缝气、泄漏流以及离散气膜对曲面端壁的气膜冷却效率的影响,并针对不同冷气流量比对端壁气膜冷效的影响规律进行了对比分析。结果表明:端壁表面气膜冷效随着槽缝气流量比增大而增大,当流量比增大到1.71%时,槽缝气膜几乎可以覆盖整个端壁表面;与槽缝气相比,端壁表面的离散气膜冷气覆盖范围较为有限,端壁压力面侧下游区域气膜覆盖较差;在喉部之前,随着流量比增大,离散气膜冷效呈现下降趋势;在喉部之后,随着流量比从1.3%增大到1.9%,离散气膜冷效呈现上升趋势;与仅有离散气膜相比,包含槽缝气、泄漏流、离散气膜的全气膜覆盖更为均匀,全气膜冷效的叠加使得端壁冷效相比仅有离散气膜时整体提高了93.4%。     

Deformation of viscoelastic coating in a turbulent flow

The rate and amplitude of compliant coating deformation by turbulent pressure pulsations were calculated. Complex compliance determined by a 2D model has two components: along and across the coating. Dependence of the components of dimensionless compliance on the wavelength — coating thickness ratio was determined for 0.3 < λ/H < 30 and dependence of these components on the ratio of flow velocity to velocity of wave propagation was determined for 0.1 < V/C < 10. Deformation amplitude and rate of surface displacement for the hard compliant coatings which can be used in practice were calculated within the range of 5–55 m/s for the water and air turbulent flow. The effects of the loss tangent and Poisson’s ratio of the coating material were also studied. It is shown that the mean-square displacement of their surface does not exceed the thickness of a viscous sublayer. However, the velocity of surface motion is comparable with velocity pulsations in a boundary layer near a wall. This can be a reason for drag reduction on a compliant wall. The calculated value of ratio between energy absorbed by the wall and energy dissipated within the flow because of drag was 10⁻⁴ for water and 10⁻⁶ for air. This estimate does not confirm the hypothesis explaining drag reduction by energy takeoff from the flow.     

Influence of bubbly clusters on the characteristics of the two-phase gas-liquid flow in a flat channel

Results of experimental investigation of a bubbly gas-liquid flow in horizontal and weakly inclined (from −20° to +20°) flat channel are presented. These measurements were carried out within the 0.2–1 m/s range of superficial velocities and volumetric gas flow rate ratio of up to 0.2. The hydrodynamic structure was measured by the electrochemical method with application of wall shear stress and conductivity microprobes. During the experiments signals of shear stress on the upper channel wall and local gas flow rate ratio were recorded completely. After numerical treatment of recorded signals the profiles of local gas flow rate ratio were obtained, average shear stress and its relative mean square pulsations on the upper channel wall were determined. It is shown that under the studied regimes the bubbles are grouped into clusters, and the bubbly flow is presented by alternation of bubbly clusters and single-phase liquid with separate bubbles and without them. Average wall shear stress and absolute shear stress pulsations in the range of bubbly clusters and beyond them were determined. Histograms of probability density distribution were obtained for the wall shear stress on the upper wall. It is shown that average shear stress and absolute pulsations in clusters are significantly higher than those in the flow zone free from bubbles. The work was financially supported by the Russian Foundation for Basic Research (No. 07-08-00405a).     

Heat transfer and crisis phenomena with intense boiling in the falling wave liquid films

Experimental data on heat transfer with intense evaporation in the falling films of liquid nitrogen were analysed. According to data generalization, heat transfer at evaporation becomes more intense under the precrisis modes at high heat fluxes for two studied boundary conditions on the heat-releasing surface: T _w ≈ const and q _w ≈ const. The relative contributions of conductive and convective components of heat transfer for different heat fluxes were estimated due to statistical treatment of the wave characteristics carried out by the capacitance probes for measurement of the local liquid film thickness. It was found out that heat transfer intensification is mainly caused by a drastic decrease in thermal resistance of the local zones with intensely evaporating residual layer between large waves. At that, the convective component of heat transfer related to wave perturbations on a free surface of a liquid film decreases significantly with a rise of heat fluxes. New data on pulsations of the local temperature of the heat-releasing surface were obtained at different points along the flow with the modes of “dry spot” formation. The work was financially supported by the Russian Foundation for Basic Research (grant No. 03-02-04027-NNIO-a) and DFG (Deutsche Forschungsgemeinschaft, project Nos. Re-463-37-1 and SFB-540).     

周期性压力波动对气膜孔流动特性影响的研究

针对主流周期性压力波动的非稳态气膜冷却现象,分别采用非稳态及准稳态数值模拟进行了计算,通过对比揭示了非稳态气膜冷却现象的特征。结果表明:相对于主流的压力波动,气膜孔出口受到上一个时刻压力的影响,呈现出了波动延迟特性;针对本文所研究的波形特点,压力波动一方面导致压差(二次流与主流压力差值)变化无法快速直接地影响到二次流流动,阻止了倒流的发生,使得二次流流量更加稳定;另一方面,其携带的压力波动效应使得气膜孔出口形成贴壁性较好的环向外旋涡,将喷射出去的二次流重新带回壁面,使得二次流贴敷壁面。对于某一特定的主流波动特性而言,是存在在最佳设计长径比使得气膜孔质量流量特性及防止倒流特性达到最佳。本文研究对于涡轮周期性压力波动作用下的气膜孔气膜冷却研究具有较大的意义。     

Numerical approach to new tangential slot effect on film cooling effectiveness over asymmetrical turbine blade

The focus of this numerical study is to conceive a new basic film cooling configuration in order to increase film cooling effectiveness, especially at the leading edge zone between the injection holes where cooling is mostly needed. The new configuration, resulting from the tangential slot configuration and especially adapted to the leading edge of an asymmetrical blade, is compared to the uniform slot configuration. Three alternatives geometries were proposed and numerically tested to find the configuration that provides the best film cooling effectiveness. The simulation is conducted at a fixed density ratio of 1.0 and a blowing ratio of 0.7. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. The outcomes of the numerical results indicate that the three proposed configurations allow better thermal protection because of their higher film cooling coverage. At suction side, the new configurations provide a better film cooling coverage than the baseline case. The minimal improvement is at approximately 34%, with a light superiority of case 1. At pressure side, the use of the tangential slot is especially interesting for the allowed minimum adiabatic effectiveness values between 0.3 and 0.5.     

THz振荡器双光栅开放腔的高频特性

针对双开槽的双光栅开放式谐振腔,提出了一种基于矩形波导谐振腔理论的计算方法,给出TE04模式场分布的结构设计修正公式,用于进行准光学谐振腔结构设计优化,通过增强电子注区域的电场强度,可有效提高电子效率。同时对双光栅慢波结构"冷"色散特性进行了计算,分析了不同参数对其高频特性的影响。结果表明,双光栅槽宽和电子注通道宽度的变化会对其色散特性的频带上限产生较大影响。     

气膜孔角度对动叶前缘冲击/气膜复合冷却的影响

本文针对GE-E3第一级动叶前缘的冲击/气膜复合冷却结构进行了热流耦合数值研究。采用标准k-ω湍流模型,分析了前缘气膜孔对称布置时,其角度对透平动叶前缘冲击/气膜复合冷却特性的影响;在五种冷气质量流量比(MFR=0.005,0.010,0.016,0.020,0.025)下,研究了气膜孔在不同角度(β=20°,25°,30°,40°,50°,60°)时的透平动叶前缘冷却换热效果。研究结果表明:在本文研究范围内,气膜孔角度越小,透平动叶前缘的平均综合冷却效率越高;随着冷气质量流量比增大,透平动叶前缘的平均综合冷却效率逐渐提高。     

超声速气膜冷却中激波抑制的研究

针对激波破坏超声速气膜冷却的机理,本文提出了一种壁面开孔的结构,数值研究结果表明：一方面,壁面开孔的结构能使激波作用的区域壁面附近的压力分布较均匀,从而使近壁区的马赫数分布比不开孔的壁面要高,有利于超声速气膜冷却。同时在激波的作用下,冷却气体可以通过开孔壁面的孔进入槽道内,而在槽内的下游再从孔里流出,保护下游的壁面,这...     

应用分离涡模型计算斜圆柱孔气膜冷却

分离涡模型(DES,Detached eddy simulation)兼有雷诺时均湍流模型计算量较小和大涡模拟计算精度高的优点。本文利用DES对平板单斜圆柱孔的气膜冷却进行了数值模拟,并将结果同RANS湍流模型的计算结果以及实验数据相比较,表明DES能有效弥补RANS湍流模型在计算三维不均匀非定常湍流场的不足,更接近实际地反映了气膜冷却中的流动和换热的本质规律。     

非定常尾迹对气膜冷却影响的数值研究

利用数值计算的方法研究了非定常尾迹对动叶气膜冷却效率的影响。在动叶叶片上开有5个气膜孔,重点研究了非定常尾迹对压力面第二个、吸力面第一个气膜孔周围的流场和温度场的影响。发现尾迹会使冷却气流的流向发生很大的改变,甚至发生"分流"、"逆流"的现象,这一点既和尾迹形成的低速区有关,也和气膜孔的位置有关。