Transactions of Nanjing University of Aeronautics & Astronautics
Volume 33,Issue 2,2016 Table of Contents
2016, 33(2):129-136.
Abstract:
A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions. The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer. The computational results indicate that comparing with the baseline nozzle with lobed mixer, the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit. The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies, and this reduction rises with the increase of chevron bend angle. The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level (SPL) increase which is not obvious at high frequencies. With chevron bend angle increasing, SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis) and little fluctuations at 90° and 150°. The external chevron nozzle with lobed mixer has overall sound pressure level (OASPL) reduction in varying degrees at 60° and 150°, but it has little OASPL increase at 90°.
A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions. The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer. The computational results indicate that comparing with the baseline nozzle with lobed mixer, the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit. The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies, and this reduction rises with the increase of chevron bend angle. The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level (SPL) increase which is not obvious at high frequencies. With chevron bend angle increasing, SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis) and little fluctuations at 90° and 150°. The external chevron nozzle with lobed mixer has overall sound pressure level (OASPL) reduction in varying degrees at 60° and 150°, but it has little OASPL increase at 90°.
2016, 33(2):137-146.
Abstract:
The airlines need to select the optional equipment according to their individual development demands and the manufacture′s standard specification manual when purchasing a new airplane. For this customization process, the selection theory is mainly based on qualitative analysis and quantitative analysis. The grey incidence analysis (GIA) is used for modeling, which evaluates the correlations between optional equipment and airlines′ individual demands. Meanwhile, the customization demands are quantitatively processed as different weights in evaluation index system with analytical hierarchy process. Then, the value of grey incidence degree is obtained which shows whether the optional equipment is on the purchasing list or not. Finally, two airlines′ customization demands are applied in the example of aircraft cabin′s sea ts, so two different purchasing priorities and equipment installation lists can be obtained. The results and comparisons verify the reasonable of modeling, which provides an objective scheme of aircraft equipment selection.
The airlines need to select the optional equipment according to their individual development demands and the manufacture′s standard specification manual when purchasing a new airplane. For this customization process, the selection theory is mainly based on qualitative analysis and quantitative analysis. The grey incidence analysis (GIA) is used for modeling, which evaluates the correlations between optional equipment and airlines′ individual demands. Meanwhile, the customization demands are quantitatively processed as different weights in evaluation index system with analytical hierarchy process. Then, the value of grey incidence degree is obtained which shows whether the optional equipment is on the purchasing list or not. Finally, two airlines′ customization demands are applied in the example of aircraft cabin′s sea ts, so two different purchasing priorities and equipment installation lists can be obtained. The results and comparisons verify the reasonable of modeling, which provides an objective scheme of aircraft equipment selection.
2016, 33(2):147-154.
Abstract:
A computational study on the flow development through tandem double-U-shaped-tubes compact heat exchangers inside exhaust nozzle is presented. In order to simplify the computational process on modeling the flow field, the compact heat exchanger is modeled as a porous matrix by using an isotropic porous medium assumption, which makes two-dimensional numerical simulation realistic. With the use of an existed quadratic relation which connects the pressure drop with the inlet velocity in the external part of the heat exchanger, the permeability and drag coefficient in the porous medium model are determined and a corresponding computational method validation is also made. Two schemes of tandem double-U-shaped-tubes compact heat exchangers are numerically analyzed. In relative to the baseline scheme, the modified scheme is improved by smoothing the nozzle expansion, varying heat exchanger mounting angle and installing boattail ramp at the trailing edge of the last heat exchanger. The results show that the pressure losses due to the existence of local recirculation zones and inappropriate distribution of the flow field are reduced in the modified scheme. The pressure loss coefficient is decreased from 1.7% under the baseline scheme to 1.2% under the modified scheme.
A computational study on the flow development through tandem double-U-shaped-tubes compact heat exchangers inside exhaust nozzle is presented. In order to simplify the computational process on modeling the flow field, the compact heat exchanger is modeled as a porous matrix by using an isotropic porous medium assumption, which makes two-dimensional numerical simulation realistic. With the use of an existed quadratic relation which connects the pressure drop with the inlet velocity in the external part of the heat exchanger, the permeability and drag coefficient in the porous medium model are determined and a corresponding computational method validation is also made. Two schemes of tandem double-U-shaped-tubes compact heat exchangers are numerically analyzed. In relative to the baseline scheme, the modified scheme is improved by smoothing the nozzle expansion, varying heat exchanger mounting angle and installing boattail ramp at the trailing edge of the last heat exchanger. The results show that the pressure losses due to the existence of local recirculation zones and inappropriate distribution of the flow field are reduced in the modified scheme. The pressure loss coefficient is decreased from 1.7% under the baseline scheme to 1.2% under the modified scheme.
2016, 33(2):155-165.
Abstract:
The enhanced cooling performance caused by ellipse-shaped tabs located at the outlet of the film cooling holes is conducted. Three covering ratios of ellipse-shaped tabs on film holes and four blowing ratios are studied. The results show that:(1)The heat transfer coefficient ratio is higher than that without tab, indicating that the mixing of mainstream and coolant jet provides a better coverage film on the cooling wall, but increases the local turbulence production which enhances the heat transfer coefficient; (2) When the ellipse-shaped tabs are located at the film hole outlet, there is a larger pressure drop with the ellipse tab relative to the no-tab case. Thus, the discharge coefficient with ellipse tab is lower than that without tab.
The enhanced cooling performance caused by ellipse-shaped tabs located at the outlet of the film cooling holes is conducted. Three covering ratios of ellipse-shaped tabs on film holes and four blowing ratios are studied. The results show that:(1)The heat transfer coefficient ratio is higher than that without tab, indicating that the mixing of mainstream and coolant jet provides a better coverage film on the cooling wall, but increases the local turbulence production which enhances the heat transfer coefficient; (2) When the ellipse-shaped tabs are located at the film hole outlet, there is a larger pressure drop with the ellipse tab relative to the no-tab case. Thus, the discharge coefficient with ellipse tab is lower than that without tab.
2016, 33(2):166-172.
Abstract:
An optimal control method based on the minimum energy of the vibration system is proposed for piezoelectric damping control of the reinforced aircraft plate. Subsequently, the dynamic equations of the piezoelectric damping reinforced plate system and the state space equations are derived. The method to determine the weight matrix of the system is presented based on the minimum energy of the vibration system. In order to obtain the optimal controller, the control parameters of the feedback controller are obtained by using the optimal method. A piezoelectric vibration optimal control experiment platform is designed to control the vibration of reinforced aircraft plate. The experimental results show that the method has good control performances.
An optimal control method based on the minimum energy of the vibration system is proposed for piezoelectric damping control of the reinforced aircraft plate. Subsequently, the dynamic equations of the piezoelectric damping reinforced plate system and the state space equations are derived. The method to determine the weight matrix of the system is presented based on the minimum energy of the vibration system. In order to obtain the optimal controller, the control parameters of the feedback controller are obtained by using the optimal method. A piezoelectric vibration optimal control experiment platform is designed to control the vibration of reinforced aircraft plate. The experimental results show that the method has good control performances.
2016, 33(2):173-179.
Abstract:
Refueling docking at different velocities is simulated by using computational fluid dynamics (CFD) method. The Osher scheme and S-A turbulence model are used to solve the compressible Navier-Stokes equations, and the Delaunay mapping dynamic grid method is also employed. All the numerical results show that the velocity of refueling docking is very important for aerial refueling. When the velocity is lower than 3 m/s, the refueling drogue will move upward with obvious cycle staggering, while moving upward with slight cycle staggering at the speed of 3 m/s. The results can be referenced by aerial refueling design.
Refueling docking at different velocities is simulated by using computational fluid dynamics (CFD) method. The Osher scheme and S-A turbulence model are used to solve the compressible Navier-Stokes equations, and the Delaunay mapping dynamic grid method is also employed. All the numerical results show that the velocity of refueling docking is very important for aerial refueling. When the velocity is lower than 3 m/s, the refueling drogue will move upward with obvious cycle staggering, while moving upward with slight cycle staggering at the speed of 3 m/s. The results can be referenced by aerial refueling design.
2016, 33(2):180-186.
Abstract:
A novel cooling system with cooling channels is proposed for the stator of 3 MW wind-driven generator. An experimental platform is built to investigate the performance of the cooling system with different loads. At 30%, 50% or 80% generator loads, the temperatures meet the design requirement. However, it is a little over the requirement at 100% load, duo to experimental errors and some unknown thermal resistances. In the test at 100% load, the developing trends of the parameters of these two generators are similar and only minor differences occurs when they reach steady state our work can be benefit for the design and improvement of MW wind-driven generator cooling solutions.
A novel cooling system with cooling channels is proposed for the stator of 3 MW wind-driven generator. An experimental platform is built to investigate the performance of the cooling system with different loads. At 30%, 50% or 80% generator loads, the temperatures meet the design requirement. However, it is a little over the requirement at 100% load, duo to experimental errors and some unknown thermal resistances. In the test at 100% load, the developing trends of the parameters of these two generators are similar and only minor differences occurs when they reach steady state our work can be benefit for the design and improvement of MW wind-driven generator cooling solutions.
2016, 33(2):187-198.
Abstract:
Optimization of the parameters of landing gear systems with double-stage air springs of catapult take-off carrier-based aircraft is here studied based on the mathematical equations of the classic dual mass spring-damper dynamic model. Certain standards for both take-off and landing performance are put forward. The contradictory factors between take-off and landing processes are analyzed. The optimization of oil in the pin area and the area near the rear oil hole is performed. Then these optimized parameters are used to assess the influence of the initial pressure of the low chamber, the ratio of the high chamber to the low chamber, and the tire inflation pressure on the performance of arresting landing and catapult take-off. The influences of these parameters on carrier-based aircraft and the aircraft-carrier on aircraft catapult take-off is also assessed. Based on the results of the simulation, respective take-off criteria must be drafted considering different types of aircraft and different take-off load cases, all of which must be matched to parameters relevant to catapult take-off.
Optimization of the parameters of landing gear systems with double-stage air springs of catapult take-off carrier-based aircraft is here studied based on the mathematical equations of the classic dual mass spring-damper dynamic model. Certain standards for both take-off and landing performance are put forward. The contradictory factors between take-off and landing processes are analyzed. The optimization of oil in the pin area and the area near the rear oil hole is performed. Then these optimized parameters are used to assess the influence of the initial pressure of the low chamber, the ratio of the high chamber to the low chamber, and the tire inflation pressure on the performance of arresting landing and catapult take-off. The influences of these parameters on carrier-based aircraft and the aircraft-carrier on aircraft catapult take-off is also assessed. Based on the results of the simulation, respective take-off criteria must be drafted considering different types of aircraft and different take-off load cases, all of which must be matched to parameters relevant to catapult take-off.
2016, 33(2):199-207.
Abstract:
The structure and modeling of a novel unmanned coaxial rotor ducted fan helicopter(RDFH) are introduced, and then, based on the helicopter air dynamics and kinematics principles, a nonlinear model of the coaxial rotor ducted fan helicopter is developed and implemented on the basis of the wind tunnel experiment. After that, the helicopter′s stability and coupling characteristics of manipulation are analyzed through time-domain. Finally, a sliding mode controller (SMC) with boundary layers is developed on a hardware in the loop platform using digital signal processor (DSP) as the flight control computer. The results show that the RDFH′s tracking ability performs well under the use of proposed controller.
The structure and modeling of a novel unmanned coaxial rotor ducted fan helicopter(RDFH) are introduced, and then, based on the helicopter air dynamics and kinematics principles, a nonlinear model of the coaxial rotor ducted fan helicopter is developed and implemented on the basis of the wind tunnel experiment. After that, the helicopter′s stability and coupling characteristics of manipulation are analyzed through time-domain. Finally, a sliding mode controller (SMC) with boundary layers is developed on a hardware in the loop platform using digital signal processor (DSP) as the flight control computer. The results show that the RDFH′s tracking ability performs well under the use of proposed controller.
2016, 33(2):208-214.
Abstract:
Multi-objective optimization design of the gas-filled bag cushion landing system is investigated. Firstly, the landing process of airbag is decomposed into a adiabatic compression and a release of landing shock energy, and the differential equation of cylindrical gas-filled bag is presented from a theoretical perspective based on the ideal gas state equation and dynamic equation. Then, the effects of exhaust areas and blasting pressure on buffer characteristics are studied, taking those parameters as design variable for the multiobjective optimization problem, and the solution can be determined by comparing Pareto set, which is gained by NSGA-Ⅱ. Finally, the feasibility of the design scheme is verified by experimental results of the ground test.
Multi-objective optimization design of the gas-filled bag cushion landing system is investigated. Firstly, the landing process of airbag is decomposed into a adiabatic compression and a release of landing shock energy, and the differential equation of cylindrical gas-filled bag is presented from a theoretical perspective based on the ideal gas state equation and dynamic equation. Then, the effects of exhaust areas and blasting pressure on buffer characteristics are studied, taking those parameters as design variable for the multiobjective optimization problem, and the solution can be determined by comparing Pareto set, which is gained by NSGA-Ⅱ. Finally, the feasibility of the design scheme is verified by experimental results of the ground test.
2016, 33(2):215-223.
Abstract:
The issue of green aircraft taxiing under various taxi scenarios is studied to improve the efficiency of aircraft surface operations and reduce environmental pollution around the airport from aircraft emissions. A green aircraft taxi programming model based on multi-scenario joint optimization is built according to airport surface network topology modeling by analyzing the characteristics of aircraft operations under three different taxiing scenarios: all-engine taxi, single-engine taxi, and electronic taxi. A genetic algorithm is also used in the model to minimize fuel consumption and pollutant emissions. The Shanghai Pudong International Airport is selected as a typical example to conduct a verification analysis. Compared with actual operational data, the amount of aircraft fuel consumption and gas emissions after optimization are reduced significantly through applying the model. Under an electronic taxiing scenario, fuel consumption can be lowered by 45.3%, and hydrocarbon (HC) and carbon dioxide (CO) emissions are decreased by 80%. The results show that a green aircraft taxiing strategy that integrates taxiway optimization and electronic taxiing can effectively improve the efficiency of airport operations and reduce aircraft pollution levels in an airport′s peripheral environment.
The issue of green aircraft taxiing under various taxi scenarios is studied to improve the efficiency of aircraft surface operations and reduce environmental pollution around the airport from aircraft emissions. A green aircraft taxi programming model based on multi-scenario joint optimization is built according to airport surface network topology modeling by analyzing the characteristics of aircraft operations under three different taxiing scenarios: all-engine taxi, single-engine taxi, and electronic taxi. A genetic algorithm is also used in the model to minimize fuel consumption and pollutant emissions. The Shanghai Pudong International Airport is selected as a typical example to conduct a verification analysis. Compared with actual operational data, the amount of aircraft fuel consumption and gas emissions after optimization are reduced significantly through applying the model. Under an electronic taxiing scenario, fuel consumption can be lowered by 45.3%, and hydrocarbon (HC) and carbon dioxide (CO) emissions are decreased by 80%. The results show that a green aircraft taxiing strategy that integrates taxiway optimization and electronic taxiing can effectively improve the efficiency of airport operations and reduce aircraft pollution levels in an airport′s peripheral environment.
2016, 33(2):224-230.
Abstract:
Integrated into the development process of a chinese independent brand class sedan, optimization about occupant restraint system associated with dummy chest deceleration is studied. Based on this simulated vehicle deceleration and the target vehicle′s chest deceleration, tipped equivalent square wave (TESW) is calculated by combining t he average stiffness k of occupant restraint system and the average free flight time t* from the existant C-NCAP (China new car assessment program)tested cars. After proposing modeling regulations of occupant restraint system and establishing mathematical dynamic modelling (MADYMO) for occupant restraint system of the target vehicle, four optimization design parameters namely vent area A, load limit L, seat belt extension ratio B and pretension force Fare selected by weighted injury criteria (WIC) rule and the first-order response surface method. The four parameters have been optimized by using orthogonal test design of four factors with five levels and the optimum combination A5L1B1F5 has been chosen by range and variance analyses. The results show that occupant restraint system performance has been optimized and improved, while meeting the chest deceleration calculation peak based on TESW.
Integrated into the development process of a chinese independent brand class sedan, optimization about occupant restraint system associated with dummy chest deceleration is studied. Based on this simulated vehicle deceleration and the target vehicle′s chest deceleration, tipped equivalent square wave (TESW) is calculated by combining t he average stiffness k of occupant restraint system and the average free flight time t* from the existant C-NCAP (China new car assessment program)tested cars. After proposing modeling regulations of occupant restraint system and establishing mathematical dynamic modelling (MADYMO) for occupant restraint system of the target vehicle, four optimization design parameters namely vent area A, load limit L, seat belt extension ratio B and pretension force Fare selected by weighted injury criteria (WIC) rule and the first-order response surface method. The four parameters have been optimized by using orthogonal test design of four factors with five levels and the optimum combination A5L1B1F5 has been chosen by range and variance analyses. The results show that occupant restraint system performance has been optimized and improved, while meeting the chest deceleration calculation peak based on TESW.
2016, 33(2):231-236.
Abstract:
In order to obtain good driving performance, a driving force model is presented for non-pneumatic elastic wheel. Brush model of pneumatic tyres is introduced and the deformations of elastic supports and tread are also taken into account. The longitudinal slip rate is redefined. The grounding pressure distribution of elastic wheels is analyzed and corrected according to speed, temperature and stiffness. Then rolling resistance equation is developed. Finally, simulation is conducted by software CarSim, and the results show that the estimated values are consistent with simulation values, especially at low longitudinal slip rate. The research can help to optimize design of non-pneumatic elastic wheel.
In order to obtain good driving performance, a driving force model is presented for non-pneumatic elastic wheel. Brush model of pneumatic tyres is introduced and the deformations of elastic supports and tread are also taken into account. The longitudinal slip rate is redefined. The grounding pressure distribution of elastic wheels is analyzed and corrected according to speed, temperature and stiffness. Then rolling resistance equation is developed. Finally, simulation is conducted by software CarSim, and the results show that the estimated values are consistent with simulation values, especially at low longitudinal slip rate. The research can help to optimize design of non-pneumatic elastic wheel.
2016, 33(2):237-242.
Abstract:
An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ) process. A test is made to measure the specific area stress and stress distributions in the specific area of the workpiece are obtained. The workpiece stresses in the FSJ process are analyzed by numerical simulation method. It is found that, in the downward stage of the process, feed force and lateral force in the tool are small, almost zero, and the maximum axial force can reach 12.5 kN. In the stable joining stage, the forces acting on the tool become stabilized. Compared with the low speed, high feed speed results in small feed force and small lateral force, but large feed force in the stable joining stage. The stresses in three directions of feed direction, direction that perpendicular to butt face and direction perpendicular to the surface are obtained. The simulation stress value of measure point is obtained. Test and numerical simulation can authenticate each other. Both experimental stress values and numerical simulation stress values are credible.
An attempt is made to measure three direction forces using octagonal ring dynamometer in the 2024 aluminum alloy friction stir joining(FSJ) process. A test is made to measure the specific area stress and stress distributions in the specific area of the workpiece are obtained. The workpiece stresses in the FSJ process are analyzed by numerical simulation method. It is found that, in the downward stage of the process, feed force and lateral force in the tool are small, almost zero, and the maximum axial force can reach 12.5 kN. In the stable joining stage, the forces acting on the tool become stabilized. Compared with the low speed, high feed speed results in small feed force and small lateral force, but large feed force in the stable joining stage. The stresses in three directions of feed direction, direction that perpendicular to butt face and direction perpendicular to the surface are obtained. The simulation stress value of measure point is obtained. Test and numerical simulation can authenticate each other. Both experimental stress values and numerical simulation stress values are credible.
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