The interaction between a plane wall jet and a parallel offset jet is studied through the Large Eddy Simulation （LES）. In order to compare with the related experimental data, the offset ratio is set to be 1.0 and th...The interaction between a plane wall jet and a parallel offset jet is studied through the Large Eddy Simulation （LES）. In order to compare with the related experimental data, the offset ratio is set to be 1.0 and the Reynolds number Re is 1.0× 104 with respect to the jet height L and the exit velocity U0. The Finite Volume Method （FVM） with orthogonal-mesh （6.17× 106 nodes） is used to discretize governing equations. The large eddies are obtained directly, while the small eddies are simulated by using the Dynamic Smagorinsky-Lily Model （DSLM） and the Dynamic Kinetic energy Subgrid-scale Model （DKSM）. Comparisons between computational results and experimental data show that the DKSM is especially effective in predicting the mean stream-wise velocity, the half-width of the velocity and the decay of the maximum velocity. The variations of the mean stream-wise velocity and the turbulent intensity at several positions are also obtained, and their distributions agree well with the measurements. The further analysis of dilute characteristics focuses on the tracer concentration, such as the distributions of the concentration （i.e., C / C0 or C / C,,）, the boundary layer thickness 6c and the half-width of the concentration b., the decay of the maximum concentration （ C / Co） along the downstream direction. The turbulence mechanism is also analyzed in some aspects, such as the coherent structure, the correlation function and the Probability Density Function （PDF） of the fluctuating velocity. The results show that the interaction between the two jets is strong near the jet exit and they are fully merged after a certain distance.展开更多
In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w,...In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w, standard k-ε, RNG, and realizable k-ε model. A parametric study was performed to determine the effect of offset ratio H and the velocity ratio r on the longitudinal and transverse positions of the merge point(MP), the combined point(CP), the upper vortex center(UVC) and the lower vortex center(LVC). Correlations that predict the position of these characteristic points of the WOJ flow as a function of H and r have been provided. Results show that any increase in the velocity ratio causes a displacement of the MP, CP, UVC and LVC further upstream along the longitudinal direction. Concerning the transverse positions, the increase of velocity ratio results in a deviation of the merge point(MP) and the lower vortex center(LVC) toward the strong jet(LWJ) whereas the transverse position of combined point(CP) and the upper vortex center(UVC) is almost independent of the velocity ratio.展开更多
Experimental study and numerical simulation were performed for the averaged flow field of two closely spaced opposed jets with hot wire anemometer(HWA)and CFD software and the simulation was compared with the measurem...Experimental study and numerical simulation were performed for the averaged flow field of two closely spaced opposed jets with hot wire anemometer(HWA)and CFD software and the simulation was compared with the measurement and approximate analytic solution in the literature.The results showed that the exit velocity profile of the single jet was top-hat distribution due to the presence of boundary layers.At L<2D(where L is nozzle separation and D is nozzle diameter),bimodal distribution of exit velocity profile,low in the middle and high on both sides,was present,while such bimodal distribution of exit velocity profile was absent at L=2D.With increasing nozzle separation,the stagnation point offset of the impinging plane increased.With the same velocity ratio,stagnation point offset of the nozzles with uniform profiles was larger than that with top-hat profiles.The approximate analytic solution of the flow field of two opposed jets in the literature was only valid for the nozzles with uniform exit velocity profiles and the prediction accuracy became worse for the nozzles with top-hat exit velocity profiles.展开更多
基金supported by the Doctoral Program of Higher Education (Grant No. 20100141110028)the State Water Pollution Control and Management of Major Special Science and Technology (Grant No. 2008ZX07104-005)the National Natural Science Foundation of China (Grant Nos. 11172218,10972163,51079102)
文摘The interaction between a plane wall jet and a parallel offset jet is studied through the Large Eddy Simulation （LES）. In order to compare with the related experimental data, the offset ratio is set to be 1.0 and the Reynolds number Re is 1.0× 104 with respect to the jet height L and the exit velocity U0. The Finite Volume Method （FVM） with orthogonal-mesh （6.17× 106 nodes） is used to discretize governing equations. The large eddies are obtained directly, while the small eddies are simulated by using the Dynamic Smagorinsky-Lily Model （DSLM） and the Dynamic Kinetic energy Subgrid-scale Model （DKSM）. Comparisons between computational results and experimental data show that the DKSM is especially effective in predicting the mean stream-wise velocity, the half-width of the velocity and the decay of the maximum velocity. The variations of the mean stream-wise velocity and the turbulent intensity at several positions are also obtained, and their distributions agree well with the measurements. The further analysis of dilute characteristics focuses on the tracer concentration, such as the distributions of the concentration （i.e., C / C0 or C / C,,）, the boundary layer thickness 6c and the half-width of the concentration b., the decay of the maximum concentration （ C / Co） along the downstream direction. The turbulence mechanism is also analyzed in some aspects, such as the coherent structure, the correlation function and the Probability Density Function （PDF） of the fluctuating velocity. The results show that the interaction between the two jets is strong near the jet exit and they are fully merged after a certain distance.
文摘In the present work, we propose to numerically study a combined turbulent wall and offset jet flow(this combination will be denoted WOJ). Several turbulence models were tested in this study: the standard k-w, SST k-w, standard k-ε, RNG, and realizable k-ε model. A parametric study was performed to determine the effect of offset ratio H and the velocity ratio r on the longitudinal and transverse positions of the merge point(MP), the combined point(CP), the upper vortex center(UVC) and the lower vortex center(LVC). Correlations that predict the position of these characteristic points of the WOJ flow as a function of H and r have been provided. Results show that any increase in the velocity ratio causes a displacement of the MP, CP, UVC and LVC further upstream along the longitudinal direction. Concerning the transverse positions, the increase of velocity ratio results in a deviation of the merge point(MP) and the lower vortex center(LVC) toward the strong jet(LWJ) whereas the transverse position of combined point(CP) and the upper vortex center(UVC) is almost independent of the velocity ratio.
文摘Experimental study and numerical simulation were performed for the averaged flow field of two closely spaced opposed jets with hot wire anemometer(HWA)and CFD software and the simulation was compared with the measurement and approximate analytic solution in the literature.The results showed that the exit velocity profile of the single jet was top-hat distribution due to the presence of boundary layers.At L<2D(where L is nozzle separation and D is nozzle diameter),bimodal distribution of exit velocity profile,low in the middle and high on both sides,was present,while such bimodal distribution of exit velocity profile was absent at L=2D.With increasing nozzle separation,the stagnation point offset of the impinging plane increased.With the same velocity ratio,stagnation point offset of the nozzles with uniform profiles was larger than that with top-hat profiles.The approximate analytic solution of the flow field of two opposed jets in the literature was only valid for the nozzles with uniform exit velocity profiles and the prediction accuracy became worse for the nozzles with top-hat exit velocity profiles.
