Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numeri...Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numerical simulations were carried out by solving the axisymmetric Euler equations with the dispersion-controlled scheme implemented with moving boundary conditions. Pressure histories at various positions inside the train-tunnel simulator at different distance measured from the entrance of the simulator are recorded both numerically and experimentally, and then compared with each other for two train speeds. After the validation of nonlinear wave phenomena, detailed numerical simulations were then conducted to account for the generation of compression waves near the entrance, the propagation of these waves along the train tunnel, and their gradual development into a weak shock wave. Four wave dynamic processes observed are interpreted by combining numerical results with experiments. They are: high-speed trains moving over a free terrain before entering railway tunnels; the abrupt-entering of high-speed trains into railway tunnels; the abrupt-entering of the tail of high-speed trains into railway tunnels; and the interaction of compression and expansion waves ahead of high-speed trains. The effects of train-tunnel configuration, such as the train length and the train-tunnel blockage ratio, on these wave processes have been investigated as well.展开更多
Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic pr...Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery.This refers to the ratio of the average total pressure after the intake to that of the freestream.One phenomenon that can have a large effect on this performance index is flow separation at the inlet.The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet.This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel.Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ.Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance.Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone.Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake.At the optimal laser frequency,found for this Mach number to be 10 kHz,the pressure recovery is found to increase by up to 4.7%.When the laser power added to the system is considered,this results in an overall increase in propulsive power of 2.47%.展开更多
文摘Numerical and experimental investigation on wave dynamic processes induced by high-speed trains entering railway tunnels are presented. Experiments were conducted by using a 1:250 scaled train-tunnel simulator. Numerical simulations were carried out by solving the axisymmetric Euler equations with the dispersion-controlled scheme implemented with moving boundary conditions. Pressure histories at various positions inside the train-tunnel simulator at different distance measured from the entrance of the simulator are recorded both numerically and experimentally, and then compared with each other for two train speeds. After the validation of nonlinear wave phenomena, detailed numerical simulations were then conducted to account for the generation of compression waves near the entrance, the propagation of these waves along the train tunnel, and their gradual development into a weak shock wave. Four wave dynamic processes observed are interpreted by combining numerical results with experiments. They are: high-speed trains moving over a free terrain before entering railway tunnels; the abrupt-entering of high-speed trains into railway tunnels; the abrupt-entering of the tail of high-speed trains into railway tunnels; and the interaction of compression and expansion waves ahead of high-speed trains. The effects of train-tunnel configuration, such as the train length and the train-tunnel blockage ratio, on these wave processes have been investigated as well.
文摘Research interest has been growing in recent years in supersonic transport,particularly supersonic propulsion systems.A key component of a commonly studied propulsion system,ramjets,is the air intake.For supersonic propulsion systems a major factor in the overall efficiency is the intake pressure recovery.This refers to the ratio of the average total pressure after the intake to that of the freestream.One phenomenon that can have a large effect on this performance index is flow separation at the inlet.The aim of this work is to examine how pulsed laser energy deposition can be used to improve pressure recovery performance by reducing flow separation at the inlet.This research examines the effects of pulsed laser energy deposition upstream of an intake with an axisymmetric centrebody in a Mach 1.92 indraft wind tunnel.Laser frequency was varied between 1 and 60 kHz with an energy per pulse of 5.6 mJ.Schlieren photography was used to examine the fundamental fluid dynamics while total and static pressure downstream of the intake diffuser were measured to examine the resulting effect on the performance.Schlieren imaging shows that the interaction between the laser generated thermal bubble and the leading edge shock produced by the centrebody results in a significant reduction in separation along the intake cone.Analysis of the schlieren results and the pressure results in tandem illustrate that the average separation location along the length of the centrebody directly correlates to the pressure recovery observed in the intake.At the optimal laser frequency,found for this Mach number to be 10 kHz,the pressure recovery is found to increase by up to 4.7%.When the laser power added to the system is considered,this results in an overall increase in propulsive power of 2.47%.
