Two-dimensional flow measurements behind a hot cylinder by two sets of He-Ne fiber LDVs.

The flow characteristics around a hot cylinder were 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 fibre probes of He-Ne laser Doppler velocimeter system were aligned opposite to each other on the optical axis. Scattering light was received in the forward direction by each probe. Single mode fibres are used for transmitting optics and double Bragg cells employed to measure backward flows. Fluid temperature was measured by an 80 MUm copper constantan thermocouple whose response time delay was compensated by a microcomputer. 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, but turbulence intensities in a vertical direction increase. In the wake region near the cylinder, momentum and heat transfer mechanisms in upper and lower shear layers are similar even for an asymmetric flow in the horizontal direction.