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61.
62.
Faruk Civan 《Transport in Porous Media》2007,67(2):329-334
An Arrhenius-type asymptotic-exponential function is derived to describe the temperature dependence of the power needed for
detachment of fine particles from pore walls in porous media. 相似文献
63.
64.
Pulsatile flows in a lateral aneurysm anchored on a stented and curved parent vessel 总被引:5,自引:0,他引:5
We present particle tracking velocimetry measurements and flow visualization of pulsatile flow fields in a stented cerebrovascular
lateral aneurysm model with a wide ostium anchored on a curved parent vessel. Among the stent parameters, the blocking ratioC
α ranging from 0% to 75% was selected to study its effect on the changes of intra-aneurysmal hemodynamics for the reference
of minimally invasive endovascular aneurysm treatment. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds
numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. The results
are characterized in terms of velocity vector field, coded streak images, region averaged velocity, vorticity, and wall shear
stress. A critical range ofC
α related to the inflow location as well as the shape and number of intra-aneurysmal vortices is identified. The intra-aneurysmal
flow activity, vortex strength, and wall shear stress are found to decrease with increasingC
α. Among theC
α examined,C
α=75% is the most favorable in attenuating the risk of aneurysmal rupture and promoting intra-aneurysmal thrombus. 相似文献
65.
V. N. Zaikovskii S. P. Kiselev V. P. Kiselev 《Journal of Applied Mechanics and Technical Physics》2005,46(5):670-676
Large-scale streamwise vortices in the vicinity of a perforated wall in the supersonic part of the nozzle are studied. The governing effect of gas inflow through a perforated wall on origination and parameters of streamwise vortices is experimentally established.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 68–75, September–October, 2005. 相似文献
66.
Experimental investigation on tunnel sonic boom 总被引:1,自引:0,他引:1
Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu
p
ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements. 相似文献
67.
M. T. Landahl 《Applied Scientific Research》1993,51(1-2):435-443
The evolution of an intermittently created isolated three-dimensional turbulent eddy near a wall is followed in space and time on the assumption that its structure evolves on three separate time scales, a shear interaction one, a viscous one, and a nonlinear one. The large-time limit of the solution for the shear interaction stage shows many of the observed features of the near-wall turbulence structure such as the formation of shear layers, of streaks, and of streamwise vortices. It also provides initial conditions for the viscous and nonlinear stages showing viscous decay of convected structures and the possibility of a singularity in the nonlinear development. The eddy model is also used to construct a new model for the turbulent shear stress showing strong similarity to Prandtl's mixing-length model. 相似文献
68.
69.
连续波化学激光器运转时,位于主喷管叶片内的副气流的分流管道壁面将被主喷管叶片加热而形成热壁面。通过3维的数值模拟,分析了单端、双端不同供气方式下,热壁面对分流管道流场特性的影响。热壁面将使总管气流总温沿着气流的流动方向逐渐升高,由此引起的支管入口总温的升高会降低支管的流量。无论是单端供气,还是双端供气,热壁面引起的管道流量波动幅度都要远大于绝热壁面的情况,最大波动幅度达2.16%。对进入总管的气流预热,适当增加供气总温,或将冷却管道与供气管道分开设计,气流总温变化引起的流量波动将会得到一定地抑制。 相似文献
70.
To obtain the key subelements that may influence the scaling of gas-gas injector combustor performance, the combustion performance subelements in a liquid propellant rocket engine combustor are initially analysed based on the results of a previous study on the scaling of a gas-gas combustion flowfield. Analysis indicates that inner wall friction loss and heat-flux loss are two key issues in gaining the scaling criterion of the combustion performance. The similarity conditions of the inner wall friction loss and heat-flux loss in a gas-gas combustion chamber are obtained by theoretical analyses. Then the theoretical scaling criterion was obtained for the combustion performance, but it proved to be impractical. The criterion conditions, the wall friction and the heat flux are further analysed in detail to obtain the specific engineering scaling criterion of the combustion performance. The results indicate that when the inner flowfields in the combustors are similar, the combustor wall shear stress will have similar distributions qualitatively and will be directly proportional to pc0.8 dt-0.2 quantitatively. In addition, the combustion peformance will remain unchanged. Furthermore, multi-element injector chambers with different geometric sizes and at different pressures are numerically simulated and the wall shear stress and combustion efficiencies are solved and compared with each other. A multi-element injector chamber is designed and hot-fire tested at several chamber pressures and the combustion performances are measured in a total of nine hot-fire tests. The numerical and experimental results verified the similarities among combustor wall shear stress and combustion performances at different chamber pressures and geometries, with the criterion applied. 相似文献