Coupled Heat Transfer Between High-Temperature Gas And Regenerative Cooling Structures In Scramjet Engines

The three-dimensional coupled heat transfer between high-temperature gas and regenerative cooling panels in scramjet engines were investigated both experimentally and numerically in this paper.The fundamental characteristics and influencing factors of regenerative cooling were studied and discussed combined with theoretical analysis.Different approaches have been proposed to reduce the temperature of the gas heated surface,and the mechanism and effect on temperature reduction were explored.The variation of temperature and heat flux of the regenerative cooling structure with the working state of the scramjet combustor has been specified.By decomposing the coupled heat transfer between high-temperature gas and regenerative cooling structure into the heat transfer of high-temperature gas and the heat transfer of cooling panel,the fundamental thermal environment of the combustor wall was studied.It was found that the flame is mainly stabilized at the shear layer and the recirculation zone of the flame holding cavity,the temperature filed and thermal environment of the wall were quite distinct at different areas of the scramjet engine.The thickness of boundary layer increases along the flow direction,which leads to the decrease of heat transfer coefficient of gas and heat flux of the wall along the flow direction.Both the heat transfer coefficient of gas and heat flux of the wall increase with the increase of mass flow rate and total temperature of gas,and decrease with the rise of wall temperature.The heat transfer coefficient of kerosene at supercritical pressure in the cooling channel increases nonlinearly with the bulk temperature of kerosene as a whole.However,the heat transfer coefficient decreases with the bulk temperature of kerosene when it is near the pseudo-critical temperature.For coupled heat transfer between regenerative cooling panel and kerosene of supercritical pressure,the heat flux of the heated surface decreases along the flow direction,and it is higher in the ribbed area.The heat flux of the heated surface rises with the wall temperature and mass flow rate of kerosene,while it declines with the inlet temperature of kerosene,and it hardly changes with the pressure of kerosene in the cooling channels.The convective heat transfer of high-temperature gas,the heat conduction inside the cooling panel,and the convective heat transfer of kerosene under supercritical pressure in the cooling channels were solved simultaneously in the present study,and the influencing factors of coupled heat transfer were also studied.Results indicated that the heat flux of the gas heated surface is in the order of 10~6 W/m~2.Compared with counter flow,the temperature variation of the gas heated surface in cocurrent flow is smaller and the temperature peak is lower.Parametric study indicated that the temperature and heat flux of the gas heated surface both rises with the static pressure and total temperature of gas.The heat flux of the gas heated surface increases with the mass flow rate of kerosene,while it decreases with the inlet temperature of kerosene,and it hardly changes with the pressure of kerosene.The influence of buoyancy on coupled heat transfer increases with the decline of mass flow rate of kerosene,and the rise of acceleration would further promote the influence of buoyancy.The temperature of the gas heated surface declines with the increase of thermal conductivity of the cooling panel,while the heat flux of the gas heated surface rises with that.With the increase of thermal conductivity of the cooling panel,the temperature gradient inside the cooling panel descreases,the difference of heat absorbed by different walls of the cooling channel decreases,and kerosene of low temperature gradually gathers at the center of the cooling channel.For constant total mass flow rate of kerosene,the temperature of the gas heated surface rises with the thickness of gas side wall,the width and height of the cooling channels,while heat flux of the gas heated surface decreases with the increase of these parameters.The mechanism and influencing factors of different methods on temperature reduction of the gas heated surface are explored.It was found that compared with steel cooling panel,the copper/steel cooling panel can effectively reduce the temperature of the gas heated surface by reducing the heat conduction resistance inside the cooling panel.Optimizing the internal dimensions of the cooling panel can synthetically utilize the convective heat transfer of kerosene and the heat conduction of rib,and reasonably reduce the temperature of the gas heated surface.The bump structure in the cooling channels can significantly enhance the local heat transfer of kerosene,reducing the temperature of the gas heated surface at the zone near and behind the bump,and the decrease of temperature increases with the height of the bump.When there are multiple equidistant bumps in the cooling channels,the temperature and heat flux of the gas heated surface have obvious"periodical"characteristics along the flow direction.The temperature reduction of the gas heated surface increases with the decrease of the bump spacing.The thermal insulation layer can significantly reduce the temperature and heat flux of the cooling panel.The reduction of temperature and heat flux increases with the thickness of the thermal insulation layer,and decreases with of the thermal conductivity of the thermal insulation material.Film cooling can also significantly reduce the temperature and heat flux of the gas heated surface.The film cooling efficiency increases with the mass flow rate of cooling film and the total temperature of high-temperature gas,while it decreases with the mass flow rate of high-temperature gas and the total temperature of cooling film,and it hardly changes with the injection angle of cooling film.The coupled heat transfer between high-temperature gas and regenerative cooling structure has also been experimentally studied.It was found that the temperature and heat flux of the regenerative cooling structure are closely related to the working state of the scramjet combustor.Both the incoming flow and equivalent ratio would affect the measured wall temperature and heat flux,and the wall temperature and heat flux of the cooling structure changes nonlinearly with the equivalent ratio.Although the variation trend of surface temperature and heat flux of the heat flux sensor is consistent with that of the regenerative cooling panel,there is still a big difference in the quantitative comparison between the measured results of the heat flux sensor and regenerative cooling panel.The heat flux of the cooling panel increases with the mass flow rate of kerosene in the experiments,while the wall temperature decreases with that.As a result,the heat transfer between the near wall gas and the heat flux sensor declines,which reduces the surface temperature and heat flux of the heat flow sensor.Both the wall temperature and heat flux of the cooling panel decrease with the turning on of film cooling,and the declining rate of wall temperature decreases with the distance from the outlet of the cooling film.The film cooling effectiveness increases with the film pressure,and declines along the flow direction as a whole.