采用LES(large eddy simulation)+FW-H(Ffowcs Williams-Hawkings)方程,研究了圆柱表面使用不同PPI(pore number per inch)和厚度的多孔介质对圆柱尾迹及圆柱-翼型干涉噪声的影响,探索了多孔介质的降噪规律和机理。结果表明:多孔介质能...采用LES(large eddy simulation)+FW-H(Ffowcs Williams-Hawkings)方程,研究了圆柱表面使用不同PPI(pore number per inch)和厚度的多孔介质对圆柱尾迹及圆柱-翼型干涉噪声的影响,探索了多孔介质的降噪规律和机理。结果表明:多孔介质能稳定圆柱表面的剪切层,抑制旋涡脱落,从而削弱尾迹对下游翼型的影响,圆柱单音噪声最大可降79 dB,翼型单音峰值降低13.22 dB,宽频噪声降低20 dB;多孔材料PPI的变化对降噪效果影响较小,而厚度是影响流场模态、降噪效果及气动性能的一个关键参数;多孔材料厚度合适时,圆柱-翼型流场形态为“剪切层模态”,可有效降低湍流干涉噪声;多孔材料厚度较小时,发现了一种流场形态,即“剪切层-尾迹模态”,导致翼型噪声增大;合适的多孔介质厚度不仅降噪效果显著,对圆柱-翼型的气动性能也有改善作用。展开更多
In this paper a hybrid algorithm which combines the pattern search method and the genetic algorithm for unconstrained optimization is presented. The algorithm is a deterministic pattern search algorithm,but in the sea...In this paper a hybrid algorithm which combines the pattern search method and the genetic algorithm for unconstrained optimization is presented. The algorithm is a deterministic pattern search algorithm,but in the search step of pattern search algorithm,the trial points are produced by a way like the genetic algorithm. At each iterate, by reduplication,crossover and mutation, a finite set of points can be used. In theory,the algorithm is globally convergent. The most stir is the numerical results showing that it can find the global minimizer for some problems ,which other pattern search algorithms don＇t bear.展开更多
The two-dimensional nonlinear acoustic field of eleven exponential shaped res- onators was simulated with a computational fluid dynamics software Fluent. The influence of driving frequency and driving intensity on pre...The two-dimensional nonlinear acoustic field of eleven exponential shaped res- onators was simulated with a computational fluid dynamics software Fluent. The influence of driving frequency and driving intensity on pressure in resonator as well as its natural frequency was investigated. The relationship between natural frequency and theoretical calculation res- onance frequency was also explored. It is found that beating phenomena can be observed in the resonator when the driving frequency deviates from the natural frequency. Moreover, the natural frequency of resonator increases with the increasing of driving intensity, which shows a hard spring effect. However, the driving intensity plays little effect on natural frequency and the natural frequencies are smaller than the theoretical calculation values in any driving intensity. Meanwhile, a formula between the natural frequency and its first-order resonance frequency from theoretical calculation was obtained by linear fitting for all these exponential shaped resonators under consideration. It is also found that the highest pressure amplitude and highest pressure ratio can be obtained from the exponential shaped resonator of m = 2.8 under the same driving intensity. Moreover, the relation between natural frequency and the theoretical resonance frequency for m = 2.8-tube is slightly different from other tubes in consideration.展开更多
文摘采用LES(large eddy simulation)+FW-H(Ffowcs Williams-Hawkings)方程,研究了圆柱表面使用不同PPI(pore number per inch)和厚度的多孔介质对圆柱尾迹及圆柱-翼型干涉噪声的影响,探索了多孔介质的降噪规律和机理。结果表明:多孔介质能稳定圆柱表面的剪切层,抑制旋涡脱落,从而削弱尾迹对下游翼型的影响,圆柱单音噪声最大可降79 dB,翼型单音峰值降低13.22 dB,宽频噪声降低20 dB;多孔材料PPI的变化对降噪效果影响较小,而厚度是影响流场模态、降噪效果及气动性能的一个关键参数;多孔材料厚度合适时,圆柱-翼型流场形态为“剪切层模态”,可有效降低湍流干涉噪声;多孔材料厚度较小时,发现了一种流场形态,即“剪切层-尾迹模态”,导致翼型噪声增大;合适的多孔介质厚度不仅降噪效果显著,对圆柱-翼型的气动性能也有改善作用。
文摘In this paper a hybrid algorithm which combines the pattern search method and the genetic algorithm for unconstrained optimization is presented. The algorithm is a deterministic pattern search algorithm,but in the search step of pattern search algorithm,the trial points are produced by a way like the genetic algorithm. At each iterate, by reduplication,crossover and mutation, a finite set of points can be used. In theory,the algorithm is globally convergent. The most stir is the numerical results showing that it can find the global minimizer for some problems ,which other pattern search algorithms don＇t bear.
基金jointly supported by National Natural Science Foundation of China(51405157,51476052)Scientific Research Fund of Hunan Provincial Education Department(14C0433,14B057)
文摘The two-dimensional nonlinear acoustic field of eleven exponential shaped res- onators was simulated with a computational fluid dynamics software Fluent. The influence of driving frequency and driving intensity on pressure in resonator as well as its natural frequency was investigated. The relationship between natural frequency and theoretical calculation res- onance frequency was also explored. It is found that beating phenomena can be observed in the resonator when the driving frequency deviates from the natural frequency. Moreover, the natural frequency of resonator increases with the increasing of driving intensity, which shows a hard spring effect. However, the driving intensity plays little effect on natural frequency and the natural frequencies are smaller than the theoretical calculation values in any driving intensity. Meanwhile, a formula between the natural frequency and its first-order resonance frequency from theoretical calculation was obtained by linear fitting for all these exponential shaped resonators under consideration. It is also found that the highest pressure amplitude and highest pressure ratio can be obtained from the exponential shaped resonator of m = 2.8 under the same driving intensity. Moreover, the relation between natural frequency and the theoretical resonance frequency for m = 2.8-tube is slightly different from other tubes in consideration.
