No abstract

The effects of low frequency, large amplitude sinusoidal pulsation on grid-generated turbulence (PGGT) were experimentally studied. Two-component hot wire anemometry technique was used. Pulsation did not change homogeneous, isotropic character of grid-generated turbulence.

In this study the hydraulic-thermal developing laminar swirling pipe flow is investigated numerically. Solution is based on the integral boundary layer method Uniform and solid body rotation distributions are considered for the axial and tangential velocities at the entry, respectively. Due to wall stress, viscous region is assumed to contain two boundary layers for axial and tangential velocities. Outside of the boundary layers’ edge the flow pattern is considered to remains uniform in axial direction and forced vortex in tangential direction. Inside boundary layers parabolic velocity and temperature profiles were considered for axi-symmetric flow pattern with uniform heat flux (UHF) condition on the pipe wall. Making use of the fourth-order Runge-Kutta scheme, the numerical solution of the governing differential equations is obtained. As an alternative solution, a CFD analysis based on the finite-volume method, has been done. Finally validity of the numerical results was checked with those obtained by CFD.

Influences of three typical vortex generators on flow pattern and ensuing heat transfer augmentation were investigated and compared at similar Re and swirl numbers inlet conditions. Studied swirlers such as propeller swirlers, jet-type swirlers, and rotating honeycombs were installed at the pipe inlet. Reynolds number ranges from 10000 to 30000. Swirlers were set on the swirl numbers 1.4, 0.89, and 0.52, which were obtained by propellers. This study has been carried out under uniform heat flux condition and air was employed as the working fluid. The obtained results provide the individual effects of each swirler configuration on mean flow and turbulence distribution as well as on enhancement of heat transfer. Considering S=1.4, jet-type swirlers pointed 133 per cent Nu enhancement compared to axial flow, whereas propellers and rotating honeycombs approached 105 per cent and 79 per cent, respectively. For S=0.89, relative treatment has been changed and propellers with 70 per cent Nu augmentation demonstrated tip-top performance behind of which other swirlers lined. By decreasing the swirl number, approximately closer heat performances were represented from all swirler configurations. Comparison of the results of various swirlers exhibited that Re and swirl numbers are not generally sufficient to determine the swirling flow characteristics and each swirler confirms an individual flow quality.