Velocity profile measurements

Figure 4.16. Free-surface velocity profiles measured on 1400° C molybdenum. The free-surface velocity profile is characterized by an 0.05 km/s amplitude elastic precursor, a plastic wave front, and a spall signal (characteristic dip) upon unloading. The dashed lines represent the expected free surface velocity based on impedance-match calculation [Duffy and Ahrens, unpublished].

Equation 11.12 does not fit velocity profiles measured in a turbulent boundary layer and an alternative approach must be used. In the simplified treatment of the flow conditions within the turbulent boundary layer the existence of the buffer layer, shown in Figure 11.1, is neglected and it is assumed that the boundary layer consists of a laminar sub-layer, in which momentum transfer is by molecular motion alone, outside which there is a turbulent region in which transfer is effected entirely by eddy motion (Figure 11.7). The approach is based on the assumption that the shear stress at a plane surface can be calculated from the simple power law developed by Blasius, already referred to in Chapter 3. 

Unfortunately, the thinness of most liquid films makes it difficult to measure the velocity profiles experimentally, since it is practically impossible to introduce any of the usual fluid-velocity probes into a film which may be less than 1 mm. thick without grossly distorting the flow patterns. Nevertheless, film velocity profile measurements have been reported for a few special cases. 

P. Douglas, Photosensitive materials for use in velocity profile measurements in the water phase of air-water systems and in single phase liquid systems, Chem. Eng. Technol, 14, 275-287 (1991). 

Velocity measurements were taken by using a laser doppler velocimeter with a green laser beam [25, 36]. Fig. 9 shows the velocity profiles measured with this... 

Figure 8.4 Mean velocity profiles measured above and within a model plastic-tree canopy (Meroney, [411]).

Measurement of inflame data provides an insight into the global characteristics of flames such as radiation and pollutant emission. Due to the inherent asymmetric nature of TDFCF, inflame measurements are usually taken along horizontal and vertical directions at various locations along the flame trajectory. This section presents a summary of data on inflame temperature, species concentration, and velocity profile measurements in TDFCF. 

Mean velocity profiles measured along the direction of crossflow at different axial locations in the flame (r—square root of momentum flux ratio). (Reprined from Han, D., and Mungal, M. G., Combustion and Flame, 133, no. 1-2,1-17, 2003. With permission from Elsevier.)... 

FIGURE 55.3 Velocity profiles measured 2 cm downstream of the aortic valve with hot film anemometry in dogs [Paulsen and Hasenkam, 1983]. The timing of the measurements during the cardiac cycle is shown by the marker on the aortic flow curve. 

On his return in 1854, Humphreys was given charge in connection with surveys for railways from Mississippi River to the Pacific. In 1857 he resumed his woih on the Mississippi delta and in 1861 published with Henry Larcam Abbot (1831-1927) a notable work on the hydraulics of this large river. The report contains numerous velocity profiles measured with the double-float method, which was later not accepted as an accurate means, however. It also contains formulae for the velocity distribution and velocity under uniform flow conditions, yet these data have not been used after aroimd 1900, mainly because of the immense problems associated with prototype observations. 

Velocity measurements close to the wall or the velocity profile measurement in the near-wall region can be used to determine the wall shear stress. Clauser proposed an approach for shear stress measurement of turbulent flow [1]. Here, the mean velocity measurements away from the wall are used with the assumption that the mean velocity (u) varies with the logarithmic distance from the wall (y), i.e.. 

Wall-bounded turbulent flows are generally subdivided in the direction normal to the wall (y coordinate). To elucidate this, the velocity profile measured in a turbulent channel flow is shown in Fig. 1 with non-dimensional coordinates (inner coordinates). The non-dimensional local mean velocity u = U/u in-... 

Chiou, C.S. and Gordon, R.J. Vortex inhibition Velocity profile measurements. Aiche Journal. 22,5 (1976) 947-950. 

The effect of turbulence on the separation in hydrocyclones has been of concern to researchers ever since the early work of Driessen. One aspect of interest is how turbulence modifies the tangential velocity profiles, i.e. its effect on the exponent n in the exponential equation for the tangential velocity in equation 2.2. Rietema " made a detailed investigation into this problem and estimated the turbulent viscosity with the aid of the tangential velocity profiles measured by KelsaU. This was done using a dimensionless parameter A ... 

Micro Laser Doppler Velodmetiy ( r-LDV), Figure 1 Application of a profile sensor(one concepf of micro-LDV) velocity profile measurement In a microchannel... 

Hahn, I., Scherer P.W., and MozeU M.M. (1993). Velocity Profiles Measured for Airflow through A Large-Scale Model of the Human Nasal Cavity. J. Appl. Physiol., Vol. 75, pp. 2273-2287. 

Hayes D G, "Tomographic Flow Measurement by Combining Component Distribution and Velocity Profile Measurements in 2 phase oil/gas flows", PhD Thesis, UMIST, May 1994. 

The velocity and pressure distribution experiment with Montz-pak (Fig. 69) has been repeated with 10 mm spacing between the packing and the wall. This open space creates wall cannels with a cross-section twice that of the triangular gas flow channels. Compartments 1 and 17, situated below tiie wall channels, are closed to avoid the direct feeding of the wall channels. The velocity profile measured at the top and the pressure profile measured at the bottom are shown in Fig. 70. From the velocity profile it is clear that only part of the gas that reaches the wall flows back into the packing. The low velocity measured for channel 6 indicates that this is more pronounced for the bottom... 

Bauer, B.O., Houser, C.A., andNiclding,W.G. 2004. Analysis of velocity profile measurements from wind-tuimel experiments with saltation. Geomorphology 59(l ) 81-98. 

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