Two parallel plane air jets and offset air jets have several common features such as the existence of a subatmospheric pressure region and the formation of a flow recirculation zone adjacent to the nozzle plate. In particular, the symmetry plane that exists between two parallel plane jets may appear to affect the flow field in much the same way as a solid wall does in a reattaching offset jet. It is obvious, however, that there are significant differences far downstream from the nozzles because the two parallel plane jets will combine to form a single free jet while the offset jet will develop into a wall jet. Differences in the near field between these two jet configurations with a separation ratio of 2.125 are examined here under identical initial flow exit conditions through laser Doppler anemometer measurements of the mean velocity components, turbulence intensities, and Reynolds shear stress. The results indicate that the wall exerts significant retarding and turbulence suppression effects on the offset jet in the flow development region. Through the use of comparisons, the interaction of two inner shear layers on both sides of the symmetry plane in two parallel plane jets results in a much more turbulent near field than that of the offset jet.
In long trains, the braking signal from locomotive control valve takes a few seconds to reach the end cars. As a result, there is a time delay in the braking of the neighbouring cars (locomotives and wagons). This causes the running of rear cars into front cars, thus producing large forces in the buffers and couplers. The induced compression and tensile forces are mainly of longitudinal nature and considered to be responsible for large amount of expenses regarding rolling stock and track repairs as well as deterioration of safety operation of the trains. The effects of the train brake delay time on longitudinal dynamic behaviour of the freight trains are investigated in this article using simulation method. The freight trains considered are those currently operating in Iranian railways. The simulations are carried out for three different cases of long, medium, and short brake application delay times. For each case, three different train forward velocities are considered. The computed results presented here include in-train compression and tensile forces. Different modes of longitudinal dynamic interactions along the train length are also observed by simulations. The results are compared in order to give some new insight into the effect of train braking delay time on train longitudinal dynamics during braking.
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