Metrology of fluid mechanics

CER66VAS32.June 1966

Measurement of terms and parameters in turbulent models

Experimental measurements of the mean and turbulent velocity field in a water flow, turn-around-duct is documented. The small radius of curvature duct experiments were made over a range of Reynolds numbers (based on a duct height of 10 cm) from 70,000 to 500,000. For this particular channel, the flow is dominated by the inertia forces. Use of the local bulk velocity to non-dimensionalize the local velocity was found to limit Reynolds number effects to the regions very close to the wall. Only secondary effects on the flow field were observed when the inlet or exit boundary conditions were altered. The flow over the central two-thirds of the channel was two-dimensional. Mean tangetial and radial velocities, streamlines, pressure distributions, surface shear stress; tangential, radial and lateral turbulent velocities and the Reynolds turbulent shear values are tabulated in other reports. It is evident from the experimental study that a complex numerical modeling technique must be developed to predict the flow in the turn-around-duct. The model must be able to predict relaminarization along the inner-convex-wall. It must also allow for the major increase in turbulence produced by the outer-concave-wall

Sites for wind power installations, technical report

CER77-78MAR-VAS4.Prepared for the United States Energy Research and Development Administration, Division of Solar Energy, Federal Wind Energy Program.Includes bibliographical references (page 27).September 1977

Experimental study of turbulent boundary layer structure, An

CER64EJP-VAS37.December 1964.Includes bibliographical references.Final Report on U.S. Army Research Grant with Meteorology Department U.S. Army Electronic Research and Development Activity, Fort Huachuca, Arizona.Under U.S. Army Research Grant DA-SIG-36-039-62-G24

Aerodynamics: a time dependent flow model for the inner region of a turbulent boundary layer

CER80-81-HCC-VAS45.Contract N00014-80-C-0183.Research carried out under Naval Sea Systems Command General Hydromechanics Research Program Subproject SR 023 01 01.Administered by David W. Taylor Naval Ship Research and Development Center.Includes bibliographical references (pages 56-59).April 1981.Response of the flow variables to external driving forces is non-linear for shear flows. For the turbulent boundary layer case, surface shear stress fluctuations of magnitude as great as the mean value are observed. For flow near the surface Prandtl's turbulent boundary layer approach of employing averaged Reynolds equation and a turbulence closure model is insufficient to account for surf ace shear fluctuations. A model which incorporates a discrete time dependent solution for the inner region of the turbulent boundary layer is proposed. The model requires stochastic averaging of the time dependent solution to account for the random aspect of the flow. The physical model for the flow near the surface is based on the bursting cycle observed in the inner region of a turbulent boundary layer. Localized pressure gradients created in the valleys of the large scale structures of the outer region of the flow are assumed to be the origin of the bursting process. This model treats the sweep motion as an impulsively started flow over a flat plate. An averaging technique is demonstrated to predict the important features of the surface shear stress. In order to confirm the time dependent model assumptions, measurements of the probability distribution and cross-correlation of the longitudinal turbulent velocity and the surface shear stress were evaluated. The sweep-scale, sweep-direction, and origin of the instability are determined from isocorrelation maps. The shape of the probability density distributions of the velocity near the surface and the surface shear stress are found to be similar. However, the velocity probability distribution changes rapidly with increasing distance from the surface. As implied by the time dependent model for the surface shear stress, the magnitude of the large surface shear stress would be substantially changed if the sweep motion could be modified. A series of thin, metal plates were employed to block the instability from reaching the surface. Results show that the mean value of surface shear and the large magnitude fluctuations of surface shear stress were reduced significantly. The variation in surface shear was found to be extremely sensitive to slight angle of attacks of the plates

Periodicity of combined heat transfer from horizontal cylinders

CER72-73SKN-VAS23.March 1973.Includes bibliographical references (pages 46-48).Prepared under Office of Naval Research Contract No. N00014-68-A-0493-0001, Project No. NR 062-414/6-6-68(Code 438), U. S. Department of Defense.Circulating copy deaccessioned 2020.Based on experimental and flow visualization studies, a model for directly opposed free and forced convection flow around a heated cylinder (0.01 mm diameter) was developed. Three modes of flow were identified. For velocities less than 15 cm/sec (cylinder Reynolds number, Redw=0.08) a free convection or a buoyant force dominated flow was observed. The interacting free convection plume and the ambient flow form a stagnation region well upstream of the heated cylinder. Heat was convected from the cylinder through the plume to the stagnation region. In the stagnation region random vortex pockets of heated mass were formed. For velocities greater than 15 cm/sec but less than 21.4 cm/sec the magnitudes of the forced and free convection flows were nearly equal. A periodic oscillation of the stagnation region was observed. The flow regime where the periodic oscillations occur was found to be defined by a specific relation between the Grashof and Reynolds numbers. The periodic oscillations, which were in the range from 3 to 15 cycles per minute, were correlated in terms of Strauhal number and Reynolds number. For velocities greater than 21.4 cm/sec the forced convection was found to dominate over the free convection. The stagnation region was fixed for each flow velocity at one position above the cylinder. A potential like flow (laminar sheet) was formed shrouding the thermal layer of the cylinder. The mean heat transfer from the cylinder decreases with increasing Reynolds number for both the case of dominant free convection and the case of equal free and forced convection. The mean heat transfer abruptly and rapidly increases with increasing Reynolds number in the forced convection dominated region. For all these cases the thermal layer surrounding the hot cylinder was approximately 600 times larger than the diameter of the cylinder

Correlation between the outer flow and the turbulent production in a boundary layer

CER74-75WCC-VAS19.May 1975.Includes bibliographical references.Space-time velocity correlation measurements between fluctuations occurring in the convoluting outer edge of a flat plate boundary layer with fluctuations occurring near the viscous subregion have been performed. The correlations indicate that information is propagated from the outer region to the inner region. The migration of turbulence away from the wall has been previously studied in the open literature. The results presented in this report along with the migration results lend support to the "limit cycle" model for turbulence production