TWO-DIMENSIONAL FLOW MEASUREMENTS BEHIND A HOT CYLINDER BY TWO SETS OF He-Ne FIBER LDVs.

The flow characteristics around a hot cylinder have been investigated in connection with the buoyancy effect on heat transfer coefficient and turbulent wake behind a hot cylinder submerged horizontally in a water channel. For simultaneous measurements of two-component velocities, two fiber probes of He-Ne LDV system were aligned opposite to each other on the optical axis. Scattering light was received in the forward direction by each probe. Single-mode fibers were used for transmitting optics and double Bragg cells were employed to measure backward flows. The results indicated that the buoyancy force due to an increase in heat flux enhances local heat transfer coefficients at the back face of the cylinder, wherein turbulence intensities in a vertical direction increase. It is pointed out that the buoyancy effect mainly contributes to the velocity and its fluctuation, temperature, and turbulent heat flux in the vertical direction.