دانلود کتاب Isothermal and Non-Isothermal Turbulent Flow over Solid Waves Transport and Structure

An experimental study on transport phenomena in a turbulent flow withseparation in a wide water channel (aspect ratio 12:1) is presented. Thewavy bottom wall, characterized by the wavelength ♥ and the wave amplitude2a, is heated with a constant heat flux under non-isothermalcondition. Spatiotemporal information on the flow velocity is obtainedfrom digital particle image velocimetry (PIV). Digital particle imagethermometry (PIT) is used to assess simultaneously the temporal andspatial variation of velocity and temperature fields. The temperatureis measured with thermochromic liquid crystal particles (TLC) whichchange their reflected wavelengths as a function of the temperature.At isothermal conditions, measurements are performed at Reynolds numbersup to 20500, defined with the bulk velocity and the half-height of thechannel. Large ensembles of instantaneous velocity fields are decomposedinto orthogonal eigenfunctions. A projection of instantaneous snapshotsof the velocity field onto eigenfunctions is used to extract the time developmentof flow structures of defined kinetic energy. Large longitudinalstructures with a characteristic spanwise scale O{1.5Λ} can be foundby projecting instantaneous realizations of the flow onto the first twoeigenfunctions. Any interactions between coherent structures result in amerger into newer structures via complete, partial, and fractional pairingsor divisions. The structures retain the characteristic separation andcontribute significantly to the kinetic energy. The meandering motion ofO{1.5♥Λ}-scales provides a mechanism for the transport of momentum.To quantify how turbulence statistics and eigenfunctions in the outer part of the shear layer depend on the interaction with the wall, threewavy surfaces, characterized by different amplitude-to-wavelength ratios,are investigated. Similar dominant eigenfunctions with similar spanwisescales are obtained in the outer part of the wall shear layer. Theroot-mean-square of the streamwise and spanwise velocity fluctuations,Reynolds shear stress, Reynolds stress coefficients, and turbulent kineticenergy are approximately the same regardless the surface roughness,when normalized with the friction velocity. The structure of stress producingmotions in the outer flow could have a universal character, inthat they are influenced by turbulence producing processes in the innerflow only through the magnitude of the friction velocity.