In the present survey, various methods for the acoustic design of aeroengine nacelle are first briefly introduced along with the comments on their advantages and disadvantages for practi- cal application, and then det...In the present survey, various methods for the acoustic design of aeroengine nacelle are first briefly introduced along with the comments on their advantages and disadvantages for practi- cal application, and then detailed analysis and discussion focus on a kind of new method which is called ＂transfer element method＂ （TEM） with emphasis on its application in the following three problems： turbomachinery noise generations, sound transmission in ducts and radiation from the inlet and outlet of ducts, as well as the interaction between them. In the theoretical frame of the TEM, the solution of acoustic field in an infinite duct with stator sound source or liner is extended to that in a finite domain with all knows and unknowns on the interface plane, and the relevant acoustic field is solved by setting up matching equation. In addition, based on combining the TEM with the boundary element method （BEM） by establishing the pressure and its derivative con- tinuum conditions on the inlet and outlet surface, the sound radiation from the inlet and outlet of ducts can also be investigated. Finally, the effects of various interactions between the sound source and acoustic treatment have been discussed in this survey. The numerical examples indicate that it is quite important to consider the effect of such interactions on sound attenuation during the acoustic design of aeroengine nacelle.展开更多
Pipes are widely used to transport gas,oil and water in industries.Drag reduction in pipes is an increasingly concerned problem to save energy.Some researches have indicated that the non-smooth surface with special st...Pipes are widely used to transport gas,oil and water in industries.Drag reduction in pipes is an increasingly concerned problem to save energy.Some researches have indicated that the non-smooth surface with special structures can reduce flow loss.In this paper,an experimental investigation has been performed on the effects of a kind of surface groove on the drag in both rectangular and circular duct at different Reynolds numbers.In the experiment of the rectangular duct,total pressure at both inlet and outlet were measured.Static pressure on the wall was measured on the surface with smooth and grooved film respectively.In the circular duct,a boundary layer pressure probe was used to measure the total pressure distribution at both inlet and outlet.Four taps at inlet and outlet were used to measure static pressure.The loss coefficient is used to evaluate the effects of the surface groove on drag reduction.The experiment was conducted with the Reynolds number range from 1.28×10~4 to 2.57×10~4.The result shows a maximum drag loss reduction of approximately 2.4% in rectangular duct at Reynolds number of 2.4×10~4.A 10%reduction of pipe pressure loss by grooved surface is measured in circular duct at a Reynolds number of 3.0×10~5.展开更多
Dispersion relation of surface waves generated by a relativistic plasma stream in an infinite duct surrounded by vacuum is derived by means of relativistic Vlasov equation. The kinematic boundary condition imposed on ...Dispersion relation of surface waves generated by a relativistic plasma stream in an infinite duct surrounded by vacuum is derived by means of relativistic Vlasov equation. The kinematic boundary condition imposed on the distribution function, the specular reflection conditions on the four sides of duct, can be satisfied by placing infinite number of fictitious surface charge sheets spaced by the duct widths. By placing appropriate fictitious surface charge sheets one can effectively deal with the extended electric field introduced in the Vlasov equation and treat kinetically the surface waves in semi-infinite, slab, and duct plasmas on equal ground. The relativistic duct dispersion relation is compared with the earlier non-relativistic surface wave dispersion relation.展开更多
基金the National Natural Science Foundation of China (No. 51106005)the National Basic Research Program of China (2012CB720201)
文摘In the present survey, various methods for the acoustic design of aeroengine nacelle are first briefly introduced along with the comments on their advantages and disadvantages for practi- cal application, and then detailed analysis and discussion focus on a kind of new method which is called ＂transfer element method＂ （TEM） with emphasis on its application in the following three problems： turbomachinery noise generations, sound transmission in ducts and radiation from the inlet and outlet of ducts, as well as the interaction between them. In the theoretical frame of the TEM, the solution of acoustic field in an infinite duct with stator sound source or liner is extended to that in a finite domain with all knows and unknowns on the interface plane, and the relevant acoustic field is solved by setting up matching equation. In addition, based on combining the TEM with the boundary element method （BEM） by establishing the pressure and its derivative con- tinuum conditions on the inlet and outlet surface, the sound radiation from the inlet and outlet of ducts can also be investigated. Finally, the effects of various interactions between the sound source and acoustic treatment have been discussed in this survey. The numerical examples indicate that it is quite important to consider the effect of such interactions on sound attenuation during the acoustic design of aeroengine nacelle.
基金funded by the National Natural Science Foundation of China,Grant No.51161130525 and 51136003supported by the 111 Project,No.B07009
文摘Pipes are widely used to transport gas,oil and water in industries.Drag reduction in pipes is an increasingly concerned problem to save energy.Some researches have indicated that the non-smooth surface with special structures can reduce flow loss.In this paper,an experimental investigation has been performed on the effects of a kind of surface groove on the drag in both rectangular and circular duct at different Reynolds numbers.In the experiment of the rectangular duct,total pressure at both inlet and outlet were measured.Static pressure on the wall was measured on the surface with smooth and grooved film respectively.In the circular duct,a boundary layer pressure probe was used to measure the total pressure distribution at both inlet and outlet.Four taps at inlet and outlet were used to measure static pressure.The loss coefficient is used to evaluate the effects of the surface groove on drag reduction.The experiment was conducted with the Reynolds number range from 1.28×10~4 to 2.57×10~4.The result shows a maximum drag loss reduction of approximately 2.4% in rectangular duct at Reynolds number of 2.4×10~4.A 10%reduction of pipe pressure loss by grooved surface is measured in circular duct at a Reynolds number of 3.0×10~5.
文摘Dispersion relation of surface waves generated by a relativistic plasma stream in an infinite duct surrounded by vacuum is derived by means of relativistic Vlasov equation. The kinematic boundary condition imposed on the distribution function, the specular reflection conditions on the four sides of duct, can be satisfied by placing infinite number of fictitious surface charge sheets spaced by the duct widths. By placing appropriate fictitious surface charge sheets one can effectively deal with the extended electric field introduced in the Vlasov equation and treat kinetically the surface waves in semi-infinite, slab, and duct plasmas on equal ground. The relativistic duct dispersion relation is compared with the earlier non-relativistic surface wave dispersion relation.
