| As the heart of aircraft,the development level of aero-engine is the concentrated embodiment of a country’s industrial foundation,scientific and technological level and comprehensive national strength,and it is also an important strategic guarantee for national security and great power status.As one of the key components of the aeroengine combustion chamber,the good spray performance of the fuel nozzle can improve the combustion efficiency and stability of the combustion chamber,reduce the emission of pollutants,and effectively promote the improvement of the aeroengine power level.Dual-orifice pressure-swirl nozzle has the advantages of large flow regulation range,and the inner nozzle diameter is small,its oil pressure can still be high,which leads to obtain better spray quality and can meet the requirements of combustion stability and complete combustion under different working conditions of high and low pressure.Therefore,dual-orifice pressure-swirl nozzles are more and more widely used in aeroengines.Different from the existing dual-orifice pressure-swirl nozzles,which have smaller inner spray angle and larger outer spray angle,according to the design requirements,this paper designed a new type of dual-orifice pressure-swirl nozzle with similar spray angle,which can achieve the corresponding spray performance and combustion performance when the inner and outer nozzles work separately.A new automatic production line of nozzle was used to manufacture the designed nozzle,and a comprehensive test-bed for spray performance of the nozzle was established.The influence factors of spray performance,internal flow characteristics,velocity distribution characteristics and liquid distribution characteristics of the nozzle were studied by combining experimental and numerical simulation methods.Then,based on the improved surrogate model,the multi-objective optimization of the inner spray angle,liquid film thickness and mass flow rate was carried out,and the optimal combination of structural parameters corresponding to the spray performance meeting the requirements was obtained.Finally,the optimized new nozzle was verified by experiment and numerical simulation,and the optimized nozzle has been applied to an aeroengine.The main research contents are as follows:(1)Based on the principle of maximum flow,the internal flow theory of centrifugal nozzle is deduced.An internal mixing dual-orifice pressure-swirl nozzle is designed by using simplified equivalent geometry method and fuel viscosity theory,and the inner and outer nozzles have similar large spray angle.The nozzle model was processed by 3D printing to complete the process formulation,and the new automatic nozzle production line was used to process and manufacture the designed dual-orifice pressure-swirl nozzle.(2)A comprehensive test-bed for spray performance of fuel nozzle is established,which can extract and measure the spray angle,fuel supply pressure,flow rate and other parameters of high-precision nozzle.In order to ensure the accuracy and uniformity of spray angle measurement,a spray angle measurement system is designed and developed,which can complete the measurement of spray angle with minimum error sum of squares.Combined with the test-bed and the measurement system,the change rules of spray form,spray angle and mass flow rate were obtained when the inner and outer nozzles worked separately or simultaneously under different pressures.Based on the experimental data and theoretical analysis,the empirical formula and semi-empirical formula for the spray angle and the mass flow rate of the dual-orifice pressure-swirl nozzle are proposed.(3)The numerical simulation model of the real size of the dual-orifice pressureswirl nozzle was established,and the mesh independence of the calculation model was verified.The numerical simulation data and experimental data were compared and analyzed in detail to verify the accuracy of the numerical simulation method.Based on the calculation results,the internal flow characteristics,velocity distribution characteristics,pressure distribution characteristics and liquid distribution characteristics of the nozzles under different working modes were analyzed.The reasons for the spray form of the experiment test were illustrated,and the distribution of axial velocity,tangential velocity and radial velocity at the nozzle outlet were studied.And the distribution of mixing position was obtained when the inner and outer work simultaneously in different time periods.Finally,the influence of the inner nozzle structure parameters on spray angle,film thickness and mass flow rate under stable working conditions were emphatically studied.(4)The design variables(length of expansion,length of straight pipe,radius of straight pipe,expansion semi-angle and contraction semi-angle)and parameter range were determined,which affect spray performance of inner nozzle.The sample sampling was carried out by using the optimal Latin hypercube design,and the corresponding response values of the samples under stable conditions were obtained based on the numerical simulation method.The surrogate models between the design variables and spray angle,liquid film thickness and mass flow rate were established by using different surrogate model building methods.Finally,the SVR model with lower error and higher precision was selected as the surrogate model in this paper.In order to further improve the fitting precision of the surrogate model,the improved quantum particle swarm optimization algorithm was used to optimize the kernel parameters and penalty factor of the SVR algorithm.Finally,the high-precision LQPSO-SVR surrogate models of spray angle,liquid film thickness and mass flow rate of the inner nozzle were established.Based on the established surrogate model of spray performance,the cross influence and single factor influence of the key geometric structure parameters on the spray performance of the inner nozzle were discussed.The results of single factor influence were compared with the results of numerical simulation,which further verified the accuracy of the numerical simulation method and the high fitting precision of the surrogate model.(5)Based on the existing LQPSO-SVR surrogate model of spray angle,liquid film thickness and mass flow rate of the inner nozzle,a mathematical model for multiobjective optimization of the inner nozzle spray performance was established.The multi-objective particle swarm optimization algorithm was selected to optimize the inner nozzle spray performance,and the tan function mapping method was used to improve the selection method of global optimal solution,which increased the diversity of Pareto optimal solution set.In the solution set,a combination of structural parameters was selected as the new nozzle for the inner nozzle after optimization.The inner of the new nozzle was numerically simulated.Compared with the original nozzle,the spray angle of the new nozzle increased by about 4%,the mass flow rate increased by about 5%,and the liquid film thickness decreased by about 30% under different oil supply pressures.Manufactured and tested the new nozzle and compared with the original design one under stable working condition,the spray angle and the mass flow rate of the new nozzle increased by about 5% when the inner was working alone,and the mass flow rate of the new nozzle has little change when the inner and outer work at the same time,but the spray angle has increased by 3.82%,which indicates that the new nozzle has better spray performance.Compared the numerical simulation data with the experimental data of the inner of the new nozzle,it is found that the error is very small,which shows that the numerical simulation method used in this paper has high accuracy.The LQPSO-SVR surrogate model of the inner nozzle spray performance has high fitting precision and prediction performance.IMOPSO algorithm shows good optimization effect in the multi-objective optimization of the inner oil nozzle spray performance.The feasibility of the multi-objective optimization design method based on surrogate model and the combination of experiment and numerical simulation is verified,which provides a new theoretical design method for the optimization design of aero-engine nozzles,and also provides a reference method for the design of small and medium-sized aviation parts. |
PDF Full Text Request