A numerical procedure to design internal cooling of gas turbine stator blades

The continuing need to improve both the efficiency and the specific power of gas turbines requires to progressively increase the temperatures of the turbine inlet.Because the first stator blades are heavily thermally loaded, efficient blade cooling is necessary.The cooling system is particularly delicate and its design must follow these guidelines:

• •minimum thermodynamic and fluid dynamic losses;
• •limited blade temperature even for reduced cooling mass flow.

Although the problem is important, analyses of possible designs are not common in literature and many constructors refer to practical experience and to various experimental results.This paper presents a comparative investigation to determine the effects of internal and external cooling in the same blade, on the basis of different combined solutions as it often happens. The cooling model will be considered one-dimensional: the limitation in the accuracy of the results is by far overcome by the simplicity and versatility of the approach. Finally, practical hints for designing an effective cooling system are derived, with particular attention to impingement. Then, global cooling parameters and medium blade will be determined in off-design condition.     

环形HYLTE喷管叶片的简化设计及加工方法

 在不影响喷管性能的前提下,将环形HYLTE喷管叶片分解为4个1/4圆环,经过进一步简化设计后,得到只有3个截面中心共面的内部管道的1/4环形叶片。提出了两种环形HYLTE喷管叶片的加工方法：真空钎焊的方法和嵌铸的方法,并对两种方法进行了比较。对于真空钎焊的方法,进行了验证加工,测试结果表明喷管叶片焊接处气密性良好,力学性能优良,可在较高温度下正常工作。嵌铸的方法在一体化加工方面优势明显,可作为环形喷管加工的备选方法。     

环形HYLTE喷管叶片的简化设计及加工方法

在不影响喷管性能的前提下,将环形HYLTE喷管叶片分解为4个1/4圆环,经过进一步简化设计后,得到只有3个截面中心共面的内部管道的1/4环形叶片。提出了两种环形HYLTE喷管叶片的加工方法：真空钎焊的方法和嵌铸的方法,并对两种方法进行了比较。对于真空钎焊的方法,进行了验证加工,测试结果表明喷管叶片焊接处气密性良好,力学性能优良,可在较高温度下正常工作。嵌铸的方法在一体化加工方面优势明显,可作为环形喷管加工的备选方法。     

Schlieren visualization of micro gas turbine exhaust plume with different shapes of nozzle

Journal of Visualization - Schlieren visualization of the plume ejected from the microgas turbine nozzle was conducted to understand infrared signal characteristics of various shapes of the exhaust...     

Some parameters of a spark channel with preionization of the gas

Spark discharges in a preionized gas gap were studied. Preionization was produced by breaking down the spark gap directly before the main discharge, which was used to ignite fuel gas mixtures. The resulting experimental and computed data are compared with theoretical data and with results obtained in an investigation of spark discharge parameters.It is shown that, as in the case of self-breakdown, the volume energy density in discharges in a preionized gas remains constant in order of magnitude (10¹⁹ eV/cm³).The studies were carried out in order to obtain certain spark characteristics for the purpose of increasing the thermal efficiency of discharges in igniting fuel mixtures.The authors are grateful to Doctor of Engineering Sciences Professor I. V. poroikov for his advice.     

可调间隙亚纳秒气体开关的优化设计

对用于UWB-1系统的可调间隙亚纳秒气体开关进行了结构优化设计,并采用Ansoft软件分别对开关绝缘子和电极处的静电场进行了模拟。优化后的调节旋钮在实验调试中使用方便,能准确地测量开关间隙的大小。绝缘子结构优化后,局部场强集中点的最大场强降低为126.6 kV·mm-1,低于理论击穿场强,满足了绝缘要求。对优化后的亚纳秒气体开关进行了高压实验,结果表明：绝缘子处没有击穿现象发生,开关工作稳定,输出脉冲的前后沿变快且脉宽变窄。系统重复频率5 Hz运行时,优化后的脉冲前后沿和脉宽分别比优化前减小了130,120和100 ps。系统重复频率100 Hz运行时,优化后的脉宽比优化前减小了150 ps,比重复频率5 Hz运行时只增加了30 ps。     

可调间隙亚纳秒气体开关的优化设计

 对用于UWB-1系统的可调间隙亚纳秒气体开关进行了结构优化设计,并采用Ansoft软件分别对开关绝缘子和电极处的静电场进行了模拟。优化后的调节旋钮在实验调试中使用方便,能准确地测量开关间隙的大小。绝缘子结构优化后,局部场强集中点的最大场强降低为126.6 kV·mm^-1,低于理论击穿场强,满足了绝缘要求。对优化后的亚纳秒气体开关进行了高压实验,结果表明：绝缘子处没有击穿现象发生,开关工作稳定,输出脉冲的前后沿变快且脉宽变窄。系统重复频率5 Hz运行时,优化后的脉冲前后沿和脉宽分别比优化前减小了130,120和100 ps。系统重复频率100 Hz运行时,优化后的脉宽比优化前减小了150 ps,比重复频率5 Hz运行时只增加了30 ps。     

Thermographic inspection of TBC coated gas turbine blades: Discrimination between coating over-thicknesses and adhesion defects

When performing in-field tests on thermal barrier coatings (TBCs) deposited on gas turbine blades, the main problem encountered is the difficulty to correctly interpret the experimental data. The coating thickness changes, which are not regarded as anomalies, are one of the most common sources of false alarms. They are very challenging to recognize because, unlike stains, eroded areas and optical property variations, they are not detectable in the visible band. Furthermore, their thermal signal is similar to the one produced by an adhesion defect. In this paper, a procedure to reliably discriminate thickness changes and real defects is proposed. The approach is based on the analysis of the apparent effusivity profile. Preliminary results are presented and discussed.     

Comparative performance of closed cycle gas turbine engine with heat recovery using different gases

The unique features of the closed cycle gas turbine engine have been recently contributing towards its adoption in a multiplicity of applications such as power plants, space, and marine power supplies. Therefore, research is reactivated to serve its future developments.In this work, a performance analysis is carried out using different gases such as air, combustion gases, CO₂ and helium. Operating variables are turbine inlet temperature T₀₃, compressor pressure ratio R_c and inlet temperature T₀₁. A computer program is taioored to calculate specific work W_s and overall efficiency η_o over a wide range of operating variables. Results show that helium gives relatively higher W_s, but η_o starts to drop early after a low optimum R_c. Air and combustion gases offer nearly equal performance.     

Analysis of the relaxation of a nonequilibrium gas or plasma in a nozzle

An economical and consistent, in mathematical respects, method of analyzing the flow of a relaxing gas or plasma in a supersonic nozzle is developed. The method is used in analyzing the vibrational relaxation of a two-phase mixture in the nozzle of a combustion gasdynamic laser. It is shown that the use of the Gear method in the numerical integration stage permits passage of the near-equilibrium sections with a large spacing, which substantially cuts down the computing time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 99–104, July, 1979.     

Coolant film flow over the edge of a nozzle in a rarefied gas

The flow of a thin liquid film over the nozzle wall under the action of tangential friction and pressure gradient is considered. For the slow flow of the film with constant thermal physical properties, analytical dependences of the film thickness and temperature at the interface on the coordinate along the nozzle edge are derived. The flow of the film over the variable-curvature nozzle edge when the gas expands into vacuum is considered. At the initial section of the curvilinear edge, the film thickness increases in inverse proportion to the root of the friction stress at the interface. Near the end point of the nozzle, the film thickens drastically because of a decrease in the friction and, consequently, the curvature of the interface diminishes. As a result, the deceleration of the liquid by the Laplace pressure gradient drops, which causes an additional sharp growth of the thickness of the film with the possibility of its dynamic and thermal disintegration and, eventually, contamination of the spacecraft surface.     

Transmission characteristics of VAD fibers using a multiple burner with single source gas nozzle

A vapor phase axial deposition (VAD) method using a multiple burner with single source gas nozzle is presented. Fibers fabricated by this technique feature very low loss and wide bandwidth characteristics, although the refractive index profile slightly deviates from the ideal, on the outer side of the core part. This technique is expected to provide a simple method of fabricating low loss and wide bandwidth fibers.