| The ability of human beings to use energy affects the development of human civilization.However,the current energy situation is that the resources of non-renewable energy are tense and the demand is still growing.Gas turbine is a kind of mechanical equipment that can use a large amount of energy and transform energy efficiently.It is known as the Pearl of the eye on the crown of industrial technology.China has lagged behind western developed countries in the design and manufacture of gas turbines for about 30 years,which is embodied in the lack of integrity design of gas turbine structure,high-temperature protection of hot-end components and uses tolerance control of key components.Therefore,the "made in China 2025 Stategy" signed and approved by the State Council in 2015 and the "several opinions on promoting gas turbine innovation and development relying on Energy Engineering" jointly issued by the national development and Reform Commission and the National Energy Administration in 2017 all emphasize the independent research and development of gas turbine core technology.Therefore,accelerating the research and development of gas turbine with independent intellectual property rights is the most important task to promote the development of heavy industry and realize the strategy of building a strong country,and also an important task to promote the economic development of our country.In this paper,the high-temperature protection effect of jet impingement cooling technology in the simplified model of double chambers in the transition section of the gas turbine is verified by combining the subproject "optimization design of transition section of stage gas turbine combustion chamber" of "863" project of the state and relying on the research on Key technologies of impingement cooling with bionic non-smooth surface structure "of National Natural Science Foundation of China.According to the flow characteristics of the cooling medium in the cooling cavity of the transition section,referring to the directional turbulence of the Alopias arch and the influence of the surface of the barchan dune on the surrounding flow field,the thermal surfaces with the turbulence structures of the alopias arch,the ribbed and the surface of the barchan dune are designed respectively.The flow field and temperature field in the cooling cavity of the transition section were studied based on the arrangement distance and structural parameter changes of the three bionic structures.The specific research content is as follows:First,based on the flow characteristics and heat transfer mechanism of the transition section of the gas turbine,the control equation and interval discrete method in computational fluid dynamics,combined with the technical characteristics of jet impingement cooling,this paper selects the realizable model which can adapt to the large time average strain rate as the turbulent calculation model in the cooling cavity of the transition section.Considering the simulation accuracy and calculation efficiency,the near-wall function is taken as the treatment method of flow calculation on the thermal surface.Based on the average temperature of the area of the thermal surface and the average temperature of the mass flow rate at the inlet and outlet of the cooling chamber,the evaluation function of the cooling efficiency on the thermal surface and in the cooling chamber is defined.Secondly,by comparing the simulation results of different turbulence models with Wang’s experimental data,the correctness and reliability of the simulation process are determined,and the realizable model is the best choice of the turbulence agent model in this paper.According to the symmetry of the transition section of the gas turbine,the heat transfer process of jet impingement cooling with cold air as the cooling medium is simplified and a general rectangular simplified model of the transition section of the gas turbine is established.By comparing the results of single hole and multi-hole jet impingement cooling,the mechanism of jet impingement cooling is analyzed,and the simplified model of the transition section of a gas turbine with multiple cooling holes is determined as the basis of comparison of subsequent research objects.At the same time,it is found that the change of air pressure in the cooling chamber is conducive to the enhancement of convective heat transfer efficiency of the thermal surface.Thirdly,inspirated by breathing process of the alopias gill in the deep sea,the thermal surfaces with one group and two groups of turbulence structures were designed in the transition section of the gas turbine.Through the Ansys-Fluent software,the heat flow field of all the simplified models with biomimetic thermal surface in the transition section of the double chamber is analyzed,and the factors affecting the high-temperature protection effect are discussed in combination with the evaluation methods of average temperature and cooling efficiency.The simulation results with a group of simulated gill bow turbulence structures show that the arrangement of simulated gill bow turbulence structure downstream of the jet impinging cooling gas column can increase the formation of air vortex in the cooling cavity,effectively reduce the average temperature of the thermal surface and increase the cooling efficiency of the thermal surface.The height and width of the gill bow structure are the key factors affecting the cooling efficiency of the thermal surface.When the height h = 20.26 mm and the width W = 5.13 mm of the gill bow structure,the average temperature on the thermal surface is the lowest and the cooling efficiency is the highest,the specific values are 1154.73 K and 14.53%,respectively.The results show that the distance between the impact target and the front end of the first row is not the main factor to affect the cooling efficiency of the transition section,but the smaller the distance is,the longer the first row is,the better the structure is The effect of the front end on the flow of cooling medium is more obvious.The height and width of the two groups of gill bows are the important factors that affect the formation of the air vortex in the cooling cavity,and also the key factors that affect the cooling efficiency of the transitional cooling cavity.When width W = 5 mm and height h = 10 mm,the cooling efficiency of the cooling chamber can reach 32.5%.Fourthly,based on the research on the structure of gill bow turbulence of alopias arch and the influence of the barchan dune surface on the surrounding flow field,the formation principle of the barchan dune surface is studied firstly,and then the rib turbulence structure of parafin dune is designed according to the two-dimensional continuous model of the barchan dune surface established by Andreotti et al.The structure of disturbing current in the mimetic barchan dune is considered.Finally,the heat flow field of all the simplified models with bionic thermal surface in the transition section is analyzed,and the factors affecting the high-temperature protection effect are discussed by combining the evaluation methods of average temperature and cooling efficiency.The results show that the windward slope is beneficial to the formation of air vortices in the cooling cavity of the transition section,to enhance the cooling efficiency of the thermal surface,and the cooling efficiency can reach 13.79%;however,when the distance between the rib structure and the impact target is not controlled properly,the backflow vortices formed at the leeward slope will lead to the formation of "dead angle" at the slope angle,which is unfavorable Improve the cooling effect on the thermal surface here.The results show that in the cooling chamber of the transition section,the cooling medium will form air vortices in the flow direction and the tangent direction,which reduces the scope and the possibility of the formation of the "dead angle" at the leeward slope angle of the bionic structure,and improves the cooling efficiency of the cooling chamber.When the size of the structure is small,the leeward slope will not form a "dead angle",but the effect of disturbing the cooling medium is insufficient;when the size of the structure is too large,it will lead to the lack of space for the formation of air vortex;when the height of the structure is H = 8 mm,the cooling efficiency of the transition cooling cavity can reach 26.62%.Finally,the research content of this paper is summarized and the future research direction is prospected. |
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