Turbulent Velocity Profiles Research Articles

Measurements of the upstream turbulent flow during wind tunnel simulations of agricultural field burning

Mean streamwise and vertical velocities as well as streamwise and vertical turbulence intensities were measured in a combustion wind tunnel used to collect pollutant emission data for agricultural field burning. Objectives were to compare the flow field upstream of a fire to that without a fire present and to compare the wind tunnel flow upstream of a fire to field conditions. Vertical centerline traverses with an anemometer were conducted for 32 separate wind tunnel operating configurations (wind speed, position in the tunnel, with or without fire, ceiling position, and floor condition) with one replication for each configuration (total of 64 traverses). Certain configurational changes in the wind tunnel had substantial effects on the flow field. Turbulence intensities and velocity profiles (as modeled by the log law-of-the-wall to determinez0 andu* values) in the wind tunnel were comparable to those in the field as reported in the literature. Velocities and turbulence intensities were generally higher, however, with a fire present in the tunnel and all other conditions constant.

Analysis of unsteady forced convection in turbulent duct flow

The results of a theoretical analysis and experimental study of unsteady forced convection with turbulent flow in the thermal entrance region of a circular duct, subjected to a periodically varying inlet temperature, are presented. The related unsteady energy equation for the thermal entrance region is analytically solved under a general boundary condition of the fifth-kind, accounting for the effects of both external convection and wall heat capacitance. Together with empirical models for expressing both eddy viscosity and turbulent velocity profiles, the generalized integral transform technique is used to provide hybrid analytical-numerical solutions for the thermal response of the fluid with a prescribed accuracy. An experimental setup was built and used to validate the mathematical modeling wherein the thermal response of the fluid is obtained in terms of amplitudes and decay indices with respect to the inlet condition for fully developed turbulent flow, due to a sinusoidal variation of the inlet temperature. Satisfactory agreement prevailed between the theoretically and experimentally determined heat transfer characteristics for a succession of axial positions, thereby establishing the theoretical model and numerical technique. To further enhance the model's practical applicability to engineering problems, the analytical technique is extended in obtaining results on the effects of the modified Biot number, fluid-towall thermal capacitance ratio, and the Reynolds number, on the thermal response of the fluid within the temperature field, which are presented in tabular forms.

Measurements of the Turbulence Structure Downstream of a Tube Bundle at High Reynolds Numbers

Mean and turbulent velocity profiles are measured in natural gas at a static pressure of approximately 5200 kPa and a Reynolds number of around 7 × 106. These measurements are obtained by conventional hot film anemometry suitably modified for use in a natural gas environment. Measurements are taken in a 102.26 mm nominal diameter pipe following a development length of around 76D. The mean velocity profile and the turbulence intensities at this location are typical for a fully developed pipe flow. Further, measurements downstream of a 19 tube bundle flow conditioner are also presented. The tube bundle is traversed downstream of a 90 degree, long radius (r = 1.5D) elbow and the measurements are taken at 19D downstream of the elbow exit. Measurements include those of the axial mean and turbulent velocities and the integral length scales. It is found that the decay of turbulence is slower and the magnitude of the length scale is smaller in comparison to measurements at lower Reynolds numbers. Orifice meter comparisons, performed in a 19D test section (meter run), confirm earlier findings that turbulence is one of the factors that affects orifice meter accuracy.

Effect of Turbulence on Orifice Meter Performance

Mean and turbulent velocity profiles downstream of a 19-tube bundle are presented. Experiments have been carried out in 101.6-mm-dia piping configuration at prevalent atmospheric conditions with air as the fluid. The two cases considered are: one with the tube bundle placed in good flow conditions and the other with the tube bundle used as a sliding vane downstream of a single 90-deg elbow. In both cases, for various positions of the tube bundle with respect to an orifice plate, the discharge coefficient for the orifice plate has been compared to a baseline value. The results indicate that it is possible to correlate the deviations in the discharge coefficient to the mean and turbulent velocity field upstream of the orifice.

Estimates of effective surface roughness over complex terrain

Turbulence data collected in an area of three-dimensional complex terrain using instruments atteched to the tether cable of a captive balloon together with radiosonde ascents are presented. In addition, data collected using only radiosonde ascents in an area of two-dimensional complex terrain of large slope are also shown. Eddy correlation measurements of the turbulent momentum flux and wind velocity profiles are used to deduce the magnitude of the effective roughness from the drag coefficient and normalised velocity profiles. A relationship connecting the terrain characteristics and the roughness length is compared with the experimental data for both types of terrain plus previous experimental estimates of the roughness length over complex terrain. The formula taken from previous work by Grant and Mason (1990) is found to agree with the data when representing an area of order 100 km2.

Numerical Calculation of Gas and Liquid Velocities along a Vertical Flat Plate Immersed in Turbulent Two-Phase Bubbly Flow.

Gas-liquid two-phase turbulent flow along a vertical flat plate immersed in bubble flow was numerically simulated using the SIMPLER method. Prandtl's mixing length theory was applied to estimate eddy viscosity. The predicted turbulent velocity profiles were in good agreement with the measurements in a bubble flow near the vertical plate, compared with the calculated laminar velocity profiles.

A General Correlation For Turbulent Velocity Profiles Of Dilute Polymer Solutions

The writer would like to congratulate the authors for their complete and comprehensive study of turbulent velocity profiles of dilute polymer solutions. He wish to draw their attention to the similarity between the mechanisms of drag reduction due to the injection of polymers and the reduction of friction factor due to air entrainment in high velocity open channel flows.

Near‐bed sediment concentration in gravel‐bedded streams

In this paper we present an analytical model for the concentration of suspended sediments in the proximity of the bed of gravel rivers. The model is applicable to high‐gradient streams carrying sands and finer sediment particles in suspension over poorly sorted gravel beds. The analysis is carried out in terms of equations which realistically describe the velocity profile of the carrying stream and the dispersion of heavy particles in turbulent shear flows over stable gravel beds. To test our hypotheses we verified the equations using available flume and river data and evaluated their response for various combinations of bed roughness and suspended load characteristics. Our results indicate that characterization of the near‐bed concentration can be formulated in terms of a velocity defect representation of the mean turbulent velocity profile and a sediment eddy diffusivity distribution developed for sand bed rivers. The near‐bed concentration is shown to be rather sensitive to variations in the gravel bed relative roughness, the depth at which the concentration is evaluated above the virtual bed surface, and the ratio between the settling velocity of the suspended sediment and the bed shear velocity.

Transient free convection and thermal stratification in uniformly-heated partially-filled horizontal cylindrical and spherical vessels

An integral approach has been used to analyze the development of the free convection boundary layer on heated concave surfaces, such as those in horizontal cylinders or a sphere. Based on the non-dimensional laminar and turbulent velocity and temperature profiles closed form expressions for the boundary layer thickness, velocity scale as well as the boundary layer commencement after the point of instability are obtained. In addition, the mass flowrate to the thermal stratified region is given.

A general correlation for turbulent velocity profiles of dilute polymer solutions

Dilute polymer solutions of sufficiently high molecular weight generally exhibit the phenomenon of drag reduction in turbulent flows. This has been usually studied by conducting either pressure drop/flow rate measurements or axial velocity profile measurements. A general correlation, based on Prandtl's mixing length model of the form, is developed herein to correlate the velocity data obtained in a 9 mm glass tube using an LDA system. This new correlation can be used to describe the velocity data of dilute solutions of polyacrylamide, xanthan gum and polyethylene oxide. The parameters α, β and Γ are unique functions of u */〈ū〉 and are independent of polymer type, concentration, mechanical degradation and Reynolds number. Good agreement between two independent data sets and predictions of the velocity profile using the above correlation was observed.

Similarity Behavior in Transitional Boundary Layers Over a Range of Adverse Pressure Gradients and Turbulence Levels

Boundary layer transition has been investigated experimentally under low, moderate, and high free-stream turbulence levels and varying adverse pressure gradients. Under high turbulence levels and adverse pressure gradients a pronounced subtransition was present. A strong degree of similarity in intermittency distributions was observed, for all conditions, when the Narasimha procedure for determination of transition inception was used. Effects of free-stream turbulence on the velocity profile are particularly strong for the laminar boundary layer upstream of the transition region. This could reflect the influence of the turbulence on the shear stress distribution throughout the layer and this matter needs further attention. The velocity profiles in wall coordinates undershoot the turbulent wall layer asymptote near the wall over most of the transition region. The rapidity with which transition occurs under adverse pressure gradients produces strong lag effects on the velocity profile; the starting turbulent boundary layer velocity profile may depart significantly from local equilibrium conditions. The practice of deriving integral properties and skin friction for transitional boundary layers by a linear combination of laminar and turbulent values for equilibrium layers is inconsistent with the observed lag effects. The velocity profile responds sufficiently slowly to the perturbation imposed by transition that much of the anticipated drop in form factor will not have occurred prior to the completion of transition. This calls into question both experimental techniques, which rely on measured form factor to characterize transition, and boundary layer calculations, which rely on local equilibrium assumptions in the vicinity of transition.

Characterization of Injection Nozzles for Gas-Solid Flow Applications

Laser phase-doppler velocimetry measurements have been used to characterize the particle-gas sprays produced by straight-tube nozzles that simulate idealized fuel injectors for solid fuel combustion systems. Tests were conducted on two nozzle sizes, for two particle sizes, two loading ratios, and two gas velocities. The Reynolds numbers was varied from 9500 to 19000, and the Stokes number from 1.9 to 61.4. It was found that the velocities of the particles in the spray decelerate more slowly, and the velocity profiles are generally more narrow, than for a single-phase free-jet. The turbulence level of the particles in the sprays was found to be less than half the turbulence level of a single-phase free-jet, and the turbulent velocity profiles were not yet fully developed at X = 40D. The hydrodynamic characteristics of the nozzles that are the most important for combustion systems were found to be: (a) the particle spray expands radially at a cone angle of 2° (measured at the radius corresponding to the peak of the particle mass flux distribution); and (b) the nozzle pressure drop and particle mass flow can be related by a correlation that depends on loading ratio, Reynolds number, Stokes number, and the pressure drop coefficient of the nozzle for a single phase flow.

Discussion of “ Turbulent Velocity Profiles for Smooth and Rough Open Channels ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Discussion of “ <i>Turbulent Velocity Profiles for Smooth and Rough Open Channels</i> ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Discussion of “ Turbulent Velocity Profiles for Smooth and Rough Open Channels ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Discussion of “ <i>Turbulent Velocity Profiles for Smooth and Rough Open Channels</i> ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Closure to “ Turbulent Velocity Profiles for Smooth and Rough Open Channels ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Closure to “ <i>Turbulent Velocity Profiles for Smooth and Rough Open Channels</i> ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Discussion of “ Turbulent Velocity Profiles for Smooth and Rough Open Channels ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Discussion of “ <i>Turbulent Velocity Profiles for Smooth and Rough Open Channels</i> ” by M. Salih Kirkgöz (November, 1989, Vol. 115, No. 11)

Nonlinear scattering of crossed focused sound beams in the presence of turbulences—Theoretical results

A theoretical study involving the interaction of mutually perpendicular crossed continuous wave ultrasonic beams overlapping (at a common focal point) and interacting in the presence of turbulence in water leads to a prediction of the far-field radiated sum frequency pressure. Earlier experimental results [M. S. Korman and S. C. Rife, “Nonlinear Sound Scattering of Crossed Focused Beams in the Presence of Turbulence,” Proc. 13th Int. Cong. Acoust., Belgrade, Yugoslavia (1989)] measured the profile of the radiated sum frequency pressure by scanning the overlap region across the width of turbulence produced by a submerged circular water jet (Re = 8.5 × 104). In scanning, the receiver transducer unit moves fixed relative to the senders (of primary frequencies f1 = 2.05 MHz and f2 = 1.95 MHz). Pressure scans compare well with known values of the radial turbulent rms velocity profile ur (r). These results can be explained in part by modifying an existing theory [M. S. Korman and R. T. Beyer, J. Acoust. Soc. Am. 85, 611–620 (1989)] to include the effects of amplitude and phase fluctuations by turbulence on the primary beams, focusing and allowing for anisotropic turbulence. [Work supported by the Naval Academy Research Council.]

Local Convective Heat Transfer From a Heated Surface to a Planar Jet of Water With a Nonuniform Velocity Profile

Experiments have been conducted on a planar, free surface jet of water to investigate the effects of a nonuniform velocity profile on the local convection coefficient for a uniform heat flux surface. Heat transfer coefficient distributions were measured for heat fluxes ranging from 0.24 to 1.47 MW/m2 and for Reynolds numbers (based on the average nozzle velocity and nozzle width) from 15,000 to 54,000. This range of flow conditions yielded turbulent velocity profiles similar to those of channel flow. Results have been obtained for both single-phase convection and nucleate boiling. Relative to results for a uniform velocity profile, the nonuniform profile was found to enhance heat transfer significantly. However, enhancement is attributed primarily to increased levels of turbulence and only secondarily to changes in the velocity profile.

Turbulent Velocity Profiles for Smooth and Rough Open Channel Flow

Velocity measurements, using a laser‐doppler anemometer, are carried out in a fully developed, rectangular, subcritical open channel flow on smooth and rough beds. The average roughness heights of the “rough” surfaces, used in the experiments, are 1 mm, 4 mm, 8 mm, and 12 mm. A model is presented for determining the reference level of the velocity distribution on “rough” surfaces. The shear velocities are determined from velocity profiles measured close to the bed. The calculated shear velocities show an increasing tendency as the wall roughness increases. In the fully turbulent inner region on a “smooth” wall, the coefficients in the logarithmic law‐of‐the‐wall distribution take values of 2.44 and 5.5; the former corresponds to 0.41 for the von Kármán constant. The velocity‐defect expression of Coles has a profile parameter of 0.1, rather than 0.55. For “rough” channels, the representation of the overall data in terms of law‐of‐the‐wall distribution seems reasonable; however, the velocity‐defect distribution is not satisfactory.

Note on an Accurate Turbulent Velocity Profile for Use at Ship Scale

Determinations of von Karman's constant and of B0 in the law of the smooth wall are compared and the considerable disagreement is explained. One determination, however, unique in its nature, seems definitive. A turbulent velocity profile equation with revised constants and a modified wake term is fitted with high precision to measurements above Rn = 107. Calculations which employ the profile lead to planar drag coefficients about 5 percent larger at full scale than those predicted by the 1957 International Towing Tank Conference (ITTC) line.