涡轮叶片内冷结构对外部气膜冷却特性的影响研究

发布时间：2018-05-16 12:40

本文选题：涡轮叶片 + 内冷结构　；参考：《西北工业大学》2015年博士论文

【摘要】：现代高温燃气涡轮叶片常用的冷却结构为内外复合冷却结构。冷却气体在叶片内部通道流动吸热后从气膜孔喷出实施气膜冷却，因此叶片内部结构对外部气膜冷却有着重要的影响。但是，由于内、外部流动换热机理有很大差别，因此，到目前为止，这两部分的流动换热特性多是分开单独进行研究的。近年来，随着设计要求的不断提高，进行叶片冷却结构精细化设计已成为趋势，必须了解在不同内部冷却结构下的气膜冷却特性，以便于在涡轮叶片设计中进行准确的热分析。为了研究内冷结构对外部气膜冷却特性的影响，本文分别建立了有内冷结构影响的气膜冷却特性实验系统和无内冷结构影响的气膜冷却特性实验系统。对于各实验结构，建立了相应的数值模拟计算模型，分析了各结构下的流动机理。关于内冷结构影响，文中主要分析了光滑内冷通道内部横流、带肋内冷通道内部肋角度与内部肋位置三方面因素。关于光滑内冷通道内部横流的影响，文中主要对比分析了光滑横流通道结构与无内冷影响的大腔进气结构。研究表明光滑内冷通道内部横流影响下气流流动结构与大腔进气结构有明显不同：在气膜孔进口，部分内部气流会在冲击气膜孔壁面后向下流出气膜孔，，使得气膜孔进口面积相对减小；在气膜孔内部，流线呈螺旋状分布，其中贴壁处螺旋线的螺距较大，中间的螺距较小；气膜孔出口，由于气流螺旋状流动，会形成出口堵塞，并且使得气膜孔出口射流分成两股；在气膜孔下游，两股射流各自形成一组对转涡，对气膜冷却效率与换热系数分布产生较大影响。实验结果显示：小吹风比下，横流越强，冷却效率越低，大吹风比下，横流越强，冷却效率越高；对于换热系数，横流越强，换热系数越高；另外，内部有横流条件下，气流需克服自身动量旋转一定的角度流入气膜孔，在这一过程中出现较大的流动损失，流量系数减小，横流越强，气膜孔流量系数越小。关于带肋内冷通道内部肋角度的影响，文中主要对比分析了135°肋横流通道结构与45°肋横流通道结构。研究表明，肋结构的存在，使得通道内部气流发生强烈的二次旋流，不同的肋角度则导致了不同的二次旋流旋转方向：在135°肋通道中通道上部分旋涡顺时针方向旋转，与气膜孔倾斜方向相近，使得气流较易流入气膜孔；而45°肋结构中，通道上部分旋涡逆时针方向旋转，与气膜孔倾斜方向相反，气流更难流入气膜孔。内部旋流影响了气膜孔进口速度分布，135°肋结构中法向速度高速区位于进口左侧，右侧则出现负值区域，而45°肋结构正好相反。不同的进口速度分布导致了不同的孔内流动结构与出口射流结构：135°肋结构下，小吹风比下孔内流线为直线并且出口射流也只有一股，大吹风比下孔内出现部分螺旋线同时出口射流略微分开成两股；45°肋结构下，孔内为螺旋状流线，类似于光滑横流通道结构，出口速度分布与出口射流结构也比较类似。不同的肋角度下出口射流结构不同，影响了对应的耦合涡结构，导致了不同的气膜冷却效率与换热系数分布。实验结果显示：对于基础圆柱孔型，小吹风比下135°肋结构下冷却效率最高，大吹风比下两种肋结构的冷却效率均低于光滑横流通道结构，对于带展向偏角的圆柱孔型，在各吹风比下45°肋结构的气膜冷却效率均为最高；关于换热系数，两种气膜孔型下均表现为135°肋结构下的换热系数较低，45°肋结构下的换热系数较高；关于气膜孔流量系数，135°肋结构下流量系数最高，45°肋结构下流量系数最低。关于带肋内冷通道内部肋位置的影响，文中主要对比分析孔在肋后，孔在肋中和孔在肋前三种结构。随着气膜孔与肋位置相对向后移动，从靠近前一个肋（孔在肋后）到靠近后一个肋（孔在肋前），进入气膜孔的气流在通道内形成的旋流逐渐减少，在气膜孔进口截面的旋流相应减弱，进口堵塞减小，孔内速度分离略有减少，对应的气膜孔流量系数略有增大。在两种肋角度下，肋位置改变时气膜孔出口射流结构均无明显变化，因此下游气膜冷却效率与换热系数分布也基本一致。在研究光滑内冷通道内部横流和带肋内冷通道内部肋角度影响时，文中分别分析了基础圆柱孔型和带展向偏角的圆柱孔型。对比两种圆柱孔型的实验结果可以发现：在相应的四种内冷结构下，带展向偏角的圆柱孔型的流量系数均高于基础圆柱孔型；而关于气膜冷却效率，在无内冷结构与45°肋结构下，带展向偏角的圆柱孔型的气膜冷却效率高于基础圆柱孔型，但是在光滑横流通道结构与135°肋结构下气膜效率却低于基础圆柱孔型。因此，为了保持带展向偏角的圆柱孔型的高流量系数并改进气膜冷却效率，文中关于带展向偏角的圆柱孔型作出了三种改型方案：1）在气膜孔出口沿展向偏斜方向使用圆柱孔型扩张；2）在气膜孔出口沿X方向使用圆柱孔型扩张；3）综合前两种扩张形式。结果发现，改型3既能增强气膜展向覆盖，还能延缓冷却效率沿流向的下降速度，使得气膜冷却效率大幅上升。针对最佳改型（改型3），实验测量了其在光滑横流通道结构下的气膜冷却特性。结果表明，该改型在各实验工况下均能保持很好的气膜覆盖，与原带展向偏角的圆柱孔型相比，冷却效率增幅达到100%以上；同时，由于出口扩张，该孔型的流量系数略高于基本的带展向偏角的圆柱孔型。
[Abstract]:The cooling structure commonly used in modern high temperature gas turbine blades is internal and external cooling structure. The cooling gas is ejected from the air film hole after the flow of the inner passage of the blade. Therefore, the internal structure of the blade has an important influence on the external film cooling. So far, the flow and heat transfer characteristics of the two parts are studied separately. In recent years, with the continuous improvement of the design requirements, the fine design of the blade cooling structure has become a trend. It is necessary to understand the characteristics of the film cooling under different internal cooling structures so as to facilitate the accurate thermal separation in the design of turbine blades. Analysis.
In order to study the influence of internal cooling structure on the cooling characteristics of external gas film, the experimental system of air film cooling characteristics with internal cooling structure and an experimental system of air film cooling characteristics without internal cooling structure were established respectively. As for the influence of internal cooling structure, the three aspects of the internal flow in the smooth internal cooling channel, the rib angle inside the cold channel and the internal rib position are analyzed.
It is shown that the structure of smooth crossflow channel and the large cavity inlet structure without internal cooling are mainly compared and analyzed in this paper. It is shown that the flow structure of the smooth internal cooling channel is obviously different from the large cavity intake structure under the influence of the internal cross flow in the smooth inner cooling channel. The inlet area of the membrane hole is down and the inlet area of the gas film hole is reduced relatively. In the air film hole, the flow line is spirally distributed, in which the spiral distance of the spiral line at the wall is larger and the middle pitch is smaller. The exit of the gas film holes will form the outlet blockage, and the gas film hole outlet jets are divided into two strands. The two ply jets formed a group of opposite vortices on the downstream of the gas film hole, which had a great influence on the cooling efficiency and the distribution of heat transfer coefficient. The experimental results showed that the stronger the cross flow, the lower the cooling efficiency, the stronger the cross flow, the higher the cooling efficiency, and the higher the heat transfer coefficient, the higher the heat transfer coefficient, the higher the heat transfer coefficient was, the higher the heat transfer coefficient was, the higher the heat transfer coefficient was, the higher the heat transfer coefficient was, the higher the heat transfer coefficient, the higher the heat transfer coefficient; In addition, under the transverse flow condition, the air flow needs to overcome its momentum rotation and flow into the gas film hole. In this process, there is a larger flow loss, the flow coefficient decreases, the transverse flow is stronger and the flow coefficient of the gas film hole is smaller.
With regard to the influence of the internal rib angle of the inner ribbed inner ribs, the structure of the 135 degree rib crossflow channel and the cross flow channel of the 45 degree rib is mainly compared and analyzed. The study shows that the existence of the rib structure makes the airflow inside the channel strong two swirling flows, and the different rib angles lead to the different rotation direction of the two swirl flow: in the 135 degree rib channel. The part of the vortex in the middle channel rotates clockwise and is close to the inclined direction of the air film hole, which makes the air flow easier to flow into the gas film hole. In the 45 degree rib structure, the part of the vortex rotates in the direction of the clockwise direction, and the air flow is more difficult to flow into the gas film hole. The internal swirling flow affects the velocity distribution of the air film hole and the structure of the 135 degree rib. The middle and high velocity region is located on the left side of the inlet, and the negative region appears on the right side, while the 45 degree rib structure is just the opposite. The different inlet velocity distribution leads to the different flow structure and the outlet structure of the outlet. Under the 135 degree rib structure, the small blow air is a straight line in the lower hole and the outlet jet is only one, and the large blow is more than the lower hole. At present, some spiral lines are at the same time the outlet jet is slightly differential into two strands; under the 45 degree rib structure, the hole is spiral flow line, similar to the smooth crossflow channel structure. The velocity distribution of the outlet is similar to that of the outlet jet structure. The different outlet jets under different rib angles affect the corresponding coupling vortex structure and lead to different air film cooling. Efficiency and heat transfer coefficient distribution. The experimental results show that for the foundation cylindrical pass, the cooling efficiency is the highest under the smaller blow ratio under the 135 degree rib structure, and the cooling efficiency of the two rib structures under the large blowing ratio is lower than the smooth crossflow channel structure. For the cylindrical pass with the spread angle, the air film cooling efficiency of the 45 degree rib structure at each blow ratio is both. For the highest heat transfer coefficient, the heat transfer coefficient under the 135 degree rib structure is lower and the heat transfer coefficient is higher under the structure of the 45 degree rib under the structure of the two kinds of gas film, and the coefficient of flow rate of the gas film hole is the highest and the coefficient of the flow rate under the 45 degree rib is the lowest.
With regard to the influence of the internal rib position of the inner ribbed inner ribs, the paper mainly contrasts and analyses the three structures of the hole in the rib and the front of the ribs after the ribs. As the gas film hole and the rib position move backward relatively, from the front of the front ribs (after Kong Zailei) to the next rib (the hole is before the ribs), the flow of air flow into the air film hole in the channel is driven by the swirl in the channel. Gradually decreasing, the swirling flow of the inlet section of the gas film hole decreases correspondingly, the inlet blockage decreases, the velocity separation in the hole decreases slightly, and the corresponding gas film pore flow coefficient increases slightly. At the two rib angle, there is no obvious change in the outlet jet structure of the gas film hole at the change of the rib position, so the distribution of the cooling efficiency and heat transfer coefficient of the downstream gas film is also basically the same. Cause.
In the study of the internal cross flow of the smooth inner cooling channel and the internal rib angle in the inner ribbed cold channel, the cylindrical pass and the circular hole with the spread angle are analyzed in this paper. The experimental results of the two kinds of cylindrical holes can be found that the flow coefficient of the cylindrical pass with the spread angle is high under the corresponding four internal cooling structures. For the air film cooling efficiency, the air film cooling efficiency of the cylindrical pass with the uncooled structure and the 45 degree rib structure is higher than that of the foundation cylindrical pass, but the film efficiency under the smooth crossflow channel structure and the 135 degree rib structure is lower than that of the base circular cylinder. The high flow coefficient of the column pass and the improvement of the cooling efficiency of the gas film are made. In this paper, three modification schemes are made about the cylindrical hole with the spread angle. 1) the expansion of the cylindrical hole is used in the outlet of the gas film hole along the direction of deflection; 2) the expansion of the cylindrical pore in the X direction of the gas film hole; 3) the two forms of expansion. The type 3 can not only enhance the covering of the air film spreading, but also delay the cooling efficiency along the flow direction and increase the cooling efficiency of the gas film. The film cooling characteristics under the smooth crossflow channel structure are measured by the experiment. The results show that the film can keep a good film cover under the experimental conditions. Compared with the cylindrical pass with spreading angle, the increase of cooling efficiency is up to 100%. At the same time, the flow coefficient of the pass is slightly higher than that of the cylindrical pass with the spread angle.

【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：V235.1

【参考文献】