engleski

Reynolds number effects of turbulent film flows in the near-wall region

The analysis of flow of film layer of the liquids is of great interest for chemical engineering in production of photo paper, film foils etc. In order to determine characteristics of flow of film layer we chose open channel in horizontal position. The analysis of the flow field is investigated experimentally using LDA measuring technique. We started firstly with open channel where, by changing flow regimen we obtained of Re numbers in the range from 300 up to 5000 which characterizes turbulent flow. The measurements values of average and local velocities was calculated as shear velocity ut on the wall in order to define shear stress of tw. We received various results of local velocities in relation to the velocity of horizontal open channel. These experimental results show that the Reynolds number has an important role in shaping of turbulent film layer. The low-Reynolds number effects in turbulent film channel flow were further investigated experimentally using the LDA measuring technique. Effects related to the finite size of the LDA measuring control volume and an inaccuracy in the estimation of the wall shear stress from near-wall velocity measurements are discussed in detail since these can yield artificial discrepancies between the measured and simulated results.

Film flow; Laser-Doppler anemometer; Turbulent wall flows; Film thickness

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