Research And Application Of Regenerative Cooling Flow And Heat Transfer Of Hydrocarbon Fuels For Scramjet

Regenerative cooling using hydrocarbon fuels is an effective approach for scramjet thermal protection,and many works have focused on it at present.In order to design the cooling structure of scramjet,detailed researches on the three dimensional flow,heat transfer and thermal cracking of hydrocarbon fuels are needed because that the cooling structure and the problems which exist in the regenerative cooling process are complicated.Since the complex manufacture technique,cost,difficult thermal assessment and parameter measurement of regeneratively cooled scramjet,the cooling structure design can be not accomplished only by means of experiments.Detailed flow field parameters,which are used for the cooling structure design,can be obtained by the flow and heat transfer computation of hydrocarbon fuels,and this is an effective way to design the cooling structure.Focusing on this project,computational and experimental studies are carried out systemically in this paper.The researches on regenerative cooling technique of scramjet and the supercritical heat transfer and thermal cracking of hydrocarbon fuels are reviewed.The important problems and significances of regenerative cooling flow and heat transfer of hydrocarbon fuels for scramjet are discussed.A computational method for regenerative cooling flow and heat transfer of hydrocarbon fuels is established and the corresponding code is compiled.The thermophysical property variations of hydrocarbon fuels with temperature and pressure are considered.This method can be used to calculate three-dimensional supercritical flow,heat transfer and thermal cracking of hydrocarbon fuels.For solving the problem that the calculated thermophysical properties of cracked fuel are not accurate resulted by the incomplete cracking products in many researches,the modified Kumar-Kunzru chemical kinetics model consisting of twenty-four reactions(one primary reaction and twenty-three secondary reactions)and eighteen species is adopted to simulate the cracking process.Detailed distribution of cracking products including aromatics,which is the key step for estimating carbon deposit,can be obtained based on this model.A look-up table method is introduced to update the properties of cracked fuel in numerical iteration process.Data lists can be reused and expanded easily and the look-up table method can promote the computational efficiency,thus this method is fit for engineering application.The “water-table” test,electrically heated tube test and fuel-cooled panel test are conducted,and the test data is used to verify the computational method.The key problems existing in the regenerative cooling flow and heat transfer process of hydrocarbon fuels are computationally investigated.Thermal cracking effect on the fuel thermophysical properties,flow and heat transfer characteristics,secondary reaction effect on the fuel thermal cracking process,pressure effect on the fuel heat transfer and thermal cracking process,and height/width ratio effect on the fuel thermal cracking,flow and heat transfer characteristics are studied.The conclusions can support the flow and heat transfer analysis and performance evaluation of cooling structure.The flow feature inside the typical zones of scramjet sidewall panel are calculated and analyzed.By comparing the flow distribution features inside several different sidewall panels under cold state with that under thermal state,the change of coolant flow distribution are obtained and the practicability of cooling structure design using cold-design method is verified.Subsequently,the effect of local structures such as distribution groove and ribs are investigated via the computation results of more than twenty sidewall panels.A design method of cooling structure based on the coolant flow is introduced,which can susupports the manufacture and thermal assessment of the combustor.The cooling structure of a reduced-scale combustor is designed using the established method above,and the coolant flow distribution in the sidewall panel of it is improved obviously.Cooling performance evaluation for this combustor is conducted under the conditions that the Mach number and fuel/air ratio are 6.0 and 1.0 respectively.The calculated fuel temperature,fuel conversion,and structure temperature,maximum stress and strain are all in their safe working ranges.After the evaluation,eleven open-looped thermal assessment tests are carried out under fuel/air ratio of 0.4-0.82.The longest runtime is 200 s.The combustor is still in good condition after the tests,which indicates that the cooling structure design is successful and the design method is further verified.In this paper,the computational method for regenerative cooling flow and heat transfer of hydrocarbon fuels is established,and it is used to design the cooling structure.The three-dimensional supercritical flow,heat transfer and thermal cracking of hydrocarbon fuels are firstly calculated at home.The coolant flow distribution characteristics of scramjet sidewall panel are systemically studied,and a cooling structure design method based on the coolant flow is put forward.Subsequently,the cooling structure design,evaluation and thermal assessment of a reduced-scale combustor are conducted.The design method is verified via the evaluation and thermal assessment results,which indicates that the researches in this paper can support the development of regeneratively cooled scramjet.