Aiming at the change in intake air flow caused by the injection of natural gas in intake manifold if one simply replaces the gasoline injector with natural gas injector with the installing position of injector in inta...Aiming at the change in intake air flow caused by the injection of natural gas in intake manifold if one simply replaces the gasoline injector with natural gas injector with the installing position of injector in intake manifold unchanged, and also the reflection of gas toward intake manifold inlet resulted from the impingement between the injected large volumetric natural gas jet and intake valve, an impulsively started natural gas jet injected from a gas injector is characterized as a three-dimensional unsteady compressible viscous turbulent flow, based on which its transient development process is numerically analyzed using general-purpose CFD codes. The predicted velocity vector maps show a vortex, which indicates the occurrence of an unsteady state jet region, is formed downstream of the jet. A schlieren apparatus is utilized to get several groups of visible schlieren photographs of natural gas jets. In the experiment, photographs of natural gas jets taken by a CCD camera are laid in a portrait processor where the shapes, tip penetration distance and injection angles of the gas jets are investigated. Comparisons between predicted results and measurements indicate an excellent agreement between simulations and experimental results.展开更多
Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled w...Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.展开更多
基金This project is supported by Provincial Natural Science Foundation of Shandong (No.Y2000F07)Scientific Research Foundation for Returned Overseas Chinese Scholars, Education Ministry of China.
文摘Aiming at the change in intake air flow caused by the injection of natural gas in intake manifold if one simply replaces the gasoline injector with natural gas injector with the installing position of injector in intake manifold unchanged, and also the reflection of gas toward intake manifold inlet resulted from the impingement between the injected large volumetric natural gas jet and intake valve, an impulsively started natural gas jet injected from a gas injector is characterized as a three-dimensional unsteady compressible viscous turbulent flow, based on which its transient development process is numerically analyzed using general-purpose CFD codes. The predicted velocity vector maps show a vortex, which indicates the occurrence of an unsteady state jet region, is formed downstream of the jet. A schlieren apparatus is utilized to get several groups of visible schlieren photographs of natural gas jets. In the experiment, photographs of natural gas jets taken by a CCD camera are laid in a portrait processor where the shapes, tip penetration distance and injection angles of the gas jets are investigated. Comparisons between predicted results and measurements indicate an excellent agreement between simulations and experimental results.
基金supported by the National Natural Science Foundation of China (No. 11272150)
文摘Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.
