Relative turbulence intensities

In order to make measurements in reverse flow regions and in regions where relative turbulence intensities exceed 30%, a frequency shifting... 

Stream is turbulent. Torobin and Guvin AlChE J., 7,615-619 [1961]) found that the drag crisis Reynolds nnmber decreases with increasing free-stream turbulence, reaching a valne of 400 when the relative turbulence intensity, dejlned as VuVC/jj is 0.4. Here Vu is the rms fluctuating velocity and C/r is the relative velocity between the particle and the fluid. 

Fig. 5.6. Effect of relative turbulence intensity Ir on sphere drag coefficient Cd-Reprinted from Clift et al [22] with permission from Elsevier.

Global quadrature point index Relative turbulence intensity (—)... 

Vertical surface collectors can readily provide information on relative drift (e.g., the amount of drift from one field trial compared to another). However, it is difficult to obtain absolute data unless the precise collection characteristics are known for the droplet size spectrum at the point of spray collection, wind speed and air turbulence intensity. " The SDTF conducted studies in wind tunnels to compare the collection efficiency of different types of drift collector used in its field studies. These studies showed that collection efficiency on strings was several orders of magnitude higher for 0.8-mm diameter cotton string than for 2-mm diameter polyethylene line and vertical o -cellulose strips or squares. The higher collection efficiency for the cotton... 

Instead of the numerical factor 4.0 in Equation 7.10, hydrodynamic theory predicts a factor near 6.0 for the effective boundary layer thickness adjacent to a flat plate (both numbers increase about 3% per 10°C Schlichting and Gersten, 2003). However, wind tunnel measurements under an appropriate turbulence intensity, as well as field measurements, indicate that 4.0 is more suitable for leaves. This divergence from theory relates to the relatively small size of leaves, their irregular shape, leaf curl, leaf flutter, and, most important, the high turbulence intensity under field conditions. Moreover, the dependency of 6bl on /° 5, which applies to large flat surfaces, does... 

Questions of the degree of perfection of mixing have plagued the use of the concept of the well-stirred reactor. In general, high turbulence intensities, small turbulence scales, slow rates of reaction, high reactor temperatures, small amounts of heat release, and relatively weak dependences of rates on temperature favor achievement of experimental results to which the concept can be applied, since under these conditions mixing rates are enhanced in comparison with reaction rates, and influences of nonuniformities within the reactor are minimized. Further information on favorable conditions may be found in Chapter 10. 

The first test case, useful for future comparison, involved the measurements without any obstructions. That is, a typical boundary layer over a relatively smooth surface (the wind tunnel ground plane covered with plywood) was studied. No unexpected phenomena were found, thereby validating the thermal anemometry technique and acquisition algorithms employed, for flows with a predominant wind direction. For a freestream speed of / , the time-averaged velocity and turbulence intensity distributions are shown in Fig. 3.39,(A). These data allow the determination of the boundary... 

A fundamental shortcoming of the Chilton-Colburn approach for multicomponent mass transfer calculations is that the assumed dependence of [/ ] on [Sc] takes no account of the variations in the level of turbulence, embodied by r turb/, with variations in the flow conditions. The reduced distance y is a function of the Reynolds number y = (y/R )(//8) / Re consequently. Re affects the reduced mixing length defined by Eq. 10.2.21. An increase in the turbulence intensity should be reflected in a relative decrease in the influence of the molecular transport processes. So, for a given multicomponent mixture the increase in the Reynolds number should have the direct effect of reducing the effect of the phenomena of molecular diffusional coupling. That is, the ratios of mass transfer coefficients 21/ 22 should decrease as Re increases. 

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