The buoyancy effect on heat transfer in a rotating,two-pass,square channel is experimentally investigated in curent work.The classical copper plate technique is performed to measure the regional averaged heat transfer...The buoyancy effect on heat transfer in a rotating,two-pass,square channel is experimentally investigated in curent work.The classical copper plate technique is performed to measure the regional averaged heat transfer cofficients.In order to perform a fundamental research,all turbulators are removed away.Two approaches of altering Buoyancy numbers are selected:varying rotation number from 0 to 2.08 at Reynolds number ranges of 10000 to 70000,and varying inlet density ratio from 0.07 to 0.16 at Reynolds number of 10000.And thus,Buoyancy numbers range from 0 to 12.9 for both cases.According to the experimental results,the relationships between heat transfer and Buoyancy numbers are in accord with those obtained under different rotation numbers.For both leading and trailing surface,a critical Buoyancy number exists for each X/D location.Before the critical point,the effect of Buoyancy number on heat transfer is limited;but after that,the Nusselt number ratios show different increase rate.Given the same rotation number,higher wall temperature ratios with its corresponding higher Buoyancy numbers substantially enhance heat transfer on both passages.And the critical exceed-point that heat transfer from trailing surface higher than leading surface happens at the same Buoyancy number for different wall temperature ratios in the second passage.Thus,the stronger buoyancy effect promotes heat transfer enhancement at high rotation number condition.展开更多
This paper presents Reynolds stress constrained large eddy simulation(RSC-LES)method applied to a U-duct flow.Different from traditional Reynolds-averaged Navier-Stokes/detached eddy simulation(RANS/DES)hybrid method(...This paper presents Reynolds stress constrained large eddy simulation(RSC-LES)method applied to a U-duct flow.Different from traditional Reynolds-averaged Navier-Stokes/detached eddy simulation(RANS/DES)hybrid method(including DES method),the RSC-LES method solves the LES equations in the whole computation domain with the near-wall regions being constrained by a prescribed Reynolds stress.By doing so it is possible to overcome the log-law mismatch(LLM)problem in hybrid method.The RSC-LES results show better agreement with experiment result.Compared with RANS and DES,RSC-LES gives more accurate pressure coefficients and friction coefficients on the wall,because the RSC-LES method captures the separation point and reattachment point on the inner wall.The computation results show that the RSC-LES method has the potential to solve the log-law mismatch problem of RANS/DES hybrid method and predict complex phenomena of internal flow field.展开更多
In order to explore the propagation law of gas explosion in U type laneways,the propagation law of flame and shock wave in U type duct were experimentally and theoret- ically investigated.It is shown that the shock wa...In order to explore the propagation law of gas explosion in U type laneways,the propagation law of flame and shock wave in U type duct were experimentally and theoret- ically investigated.It is shown that the shock wave takes on the complicated stress state and the flame takes on complicated change rules in the U type duct.The propagation process of gas explosion in bend duct is the mutual action of explosion wave,flame and complicate flow,the destruction in bend surface is especially serious.In the mine exploita- tion and laneway design,the bend laneway should be avoided,especially continuous bend laneway.展开更多
文摘The buoyancy effect on heat transfer in a rotating,two-pass,square channel is experimentally investigated in curent work.The classical copper plate technique is performed to measure the regional averaged heat transfer cofficients.In order to perform a fundamental research,all turbulators are removed away.Two approaches of altering Buoyancy numbers are selected:varying rotation number from 0 to 2.08 at Reynolds number ranges of 10000 to 70000,and varying inlet density ratio from 0.07 to 0.16 at Reynolds number of 10000.And thus,Buoyancy numbers range from 0 to 12.9 for both cases.According to the experimental results,the relationships between heat transfer and Buoyancy numbers are in accord with those obtained under different rotation numbers.For both leading and trailing surface,a critical Buoyancy number exists for each X/D location.Before the critical point,the effect of Buoyancy number on heat transfer is limited;but after that,the Nusselt number ratios show different increase rate.Given the same rotation number,higher wall temperature ratios with its corresponding higher Buoyancy numbers substantially enhance heat transfer on both passages.And the critical exceed-point that heat transfer from trailing surface higher than leading surface happens at the same Buoyancy number for different wall temperature ratios in the second passage.Thus,the stronger buoyancy effect promotes heat transfer enhancement at high rotation number condition.
文摘This paper presents Reynolds stress constrained large eddy simulation(RSC-LES)method applied to a U-duct flow.Different from traditional Reynolds-averaged Navier-Stokes/detached eddy simulation(RANS/DES)hybrid method(including DES method),the RSC-LES method solves the LES equations in the whole computation domain with the near-wall regions being constrained by a prescribed Reynolds stress.By doing so it is possible to overcome the log-law mismatch(LLM)problem in hybrid method.The RSC-LES results show better agreement with experiment result.Compared with RANS and DES,RSC-LES gives more accurate pressure coefficients and friction coefficients on the wall,because the RSC-LES method captures the separation point and reattachment point on the inner wall.The computation results show that the RSC-LES method has the potential to solve the log-law mismatch problem of RANS/DES hybrid method and predict complex phenomena of internal flow field.
基金the National Natural Science Foundation of China(50674047,50534090,50574093)State Key Base Development Plan(2005CB221506)
文摘In order to explore the propagation law of gas explosion in U type laneways,the propagation law of flame and shock wave in U type duct were experimentally and theoret- ically investigated.It is shown that the shock wave takes on the complicated stress state and the flame takes on complicated change rules in the U type duct.The propagation process of gas explosion in bend duct is the mutual action of explosion wave,flame and complicate flow,the destruction in bend surface is especially serious.In the mine exploita- tion and laneway design,the bend laneway should be avoided,especially continuous bend laneway.
