Experimental study on drag reduction due to periodically heated wall

Abstract eng:
Flow in a channel with spatially periodic wall heating is examined experimentally at Reynolds numbers below Re:20 and at the Rayleigh number based on the amplitude of the periodic heating and the channel half width Rap:3500, to verify the super-thermohydrophobic effect leading to a friction-drag reduction. Periodic heating with a non-dimensional wavenumber of 1 is applied at the lower wall while the temperature of the upper wall is uniform and kept constant at the average temperature of lower wall. The results show that steady separation bubbles are created by periodic heating, which separate the main stream from the wall. About 12% drag reduction is found at Re:1, demonstrating that separation bubbles due to the super-thermohydrophobic effect surely contribute to the friction drag reduction.

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