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 nois...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°.展开更多
The tendency for air column resonance generation in structures with a constant volume behind a tube array like that of an exhaust gas economizer has been reported, but many points remain unclear with respect to the me...The tendency for air column resonance generation in structures with a constant volume behind a tube array like that of an exhaust gas economizer has been reported, but many points remain unclear with respect to the mechanism and conditions that generate acoustical resonance. When acoustical resonance is generated, in reality, prevention and suppression measures are implemented by inserting a baffle plate into the ducts through a process of trial and error. The purpose of this study is to clarify the mechanism of generation of acoustical resonance, and to establish an appropriate measure to prevent such resonance. Noise generated in an exhaust gas economizer was correlated with the flow inside the tube array and experimentally analyzed, and the mechanism for resonance generation was considered. In addition, the effectiveness of a baffle plate positioned in order to prevent resonance was investigated. We have successfully employed a single baffle plate to suppress resonance.展开更多
A multi-dimensional computational fluid dynamics(CFD) approach was proposed in this study aiming to calculate the transfer matrix of an engine exhaust muffler in the conditions with and without mean flow.The CFD model...A multi-dimensional computational fluid dynamics(CFD) approach was proposed in this study aiming to calculate the transfer matrix of an engine exhaust muffler in the conditions with and without mean flow.The CFD model of the muffler with absorptive material defined as porous zone was calibrated with the measured noise reduction without mean flow,and was further employed to study the effect of the mean flow on the acoustic performance of the muffler.Furthermore,the exhaust acoustical source was derived from the calculated transfer matrices of six different additional acoustic loads obtained by the proposed CFD approach as well as the measured tail noise based on a multiload least squares method.Finally,the exhaust noise was predicted based on Thevenin's theorem.The proposed CFD approach was suggested to be able to predict the acoustic performance of a complex muffler considering mean flow(without and with mean flow) and heat transfer,and provide reasonable results of the exhaust noise.展开更多
Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole s...Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole source in the intermittence exhaust noise are established. The effects of all parameters in pneumatic system on the noise are also comprehensively studied.展开更多
An active noise control (ANC) method was developed for exhaust noise reduction for medium-duty diesel trucks. A modified variable step size least mean squares (LMS) algorithm was used for the controller in a variable...An active noise control (ANC) method was developed for exhaust noise reduction for medium-duty diesel trucks. A modified variable step size least mean squares (LMS) algorithm was used for the controller in a variable environment that considered the vehicle's acceleration characteristics. The variable step size time-based synchronized filtered-x LMS method (SFX-TB) used an adaptive algorithm that was more efficient than the conventional filtered-x LMS algorithm. The simulation and the experimental tests show that the control trackability and stability provided by the algorithm during acceleration enable the ANC system to effectively reduce the vehicle exhaust noise.展开更多
文摘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°.
文摘The tendency for air column resonance generation in structures with a constant volume behind a tube array like that of an exhaust gas economizer has been reported, but many points remain unclear with respect to the mechanism and conditions that generate acoustical resonance. When acoustical resonance is generated, in reality, prevention and suppression measures are implemented by inserting a baffle plate into the ducts through a process of trial and error. The purpose of this study is to clarify the mechanism of generation of acoustical resonance, and to establish an appropriate measure to prevent such resonance. Noise generated in an exhaust gas economizer was correlated with the flow inside the tube array and experimentally analyzed, and the mechanism for resonance generation was considered. In addition, the effectiveness of a baffle plate positioned in order to prevent resonance was investigated. We have successfully employed a single baffle plate to suppress resonance.
文摘A multi-dimensional computational fluid dynamics(CFD) approach was proposed in this study aiming to calculate the transfer matrix of an engine exhaust muffler in the conditions with and without mean flow.The CFD model of the muffler with absorptive material defined as porous zone was calibrated with the measured noise reduction without mean flow,and was further employed to study the effect of the mean flow on the acoustic performance of the muffler.Furthermore,the exhaust acoustical source was derived from the calculated transfer matrices of six different additional acoustic loads obtained by the proposed CFD approach as well as the measured tail noise based on a multiload least squares method.Finally,the exhaust noise was predicted based on Thevenin's theorem.The proposed CFD approach was suggested to be able to predict the acoustic performance of a complex muffler considering mean flow(without and with mean flow) and heat transfer,and provide reasonable results of the exhaust noise.
基金Special Fund for the Whole Nation Excellent Doctorate Thesis of the Colleges and University of China.
文摘Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole source in the intermittence exhaust noise are established. The effects of all parameters in pneumatic system on the noise are also comprehensively studied.
文摘An active noise control (ANC) method was developed for exhaust noise reduction for medium-duty diesel trucks. A modified variable step size least mean squares (LMS) algorithm was used for the controller in a variable environment that considered the vehicle's acceleration characteristics. The variable step size time-based synchronized filtered-x LMS method (SFX-TB) used an adaptive algorithm that was more efficient than the conventional filtered-x LMS algorithm. The simulation and the experimental tests show that the control trackability and stability provided by the algorithm during acceleration enable the ANC system to effectively reduce the vehicle exhaust noise.
