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The effect of a dilute suspension, of near neutral-density particles, on the wall turbulence in a horizontal channel was investigated by means of a laser Doppler anemomentry and flow visualization. We found that the particles increase the period between bursts. However, due to the mixing effect of the particles and effects similar to a rough wall, the overall Reynolds stress increases somewhat near the wall. Furthermore, because of increased Reynolds stress levels within the bursts, the fraction of the Reynolds stress in the bursts remains at about the same value (∼85%) as for flows without particles. Quadrant analysis of the Reynolds stress data indicates that particles increase sweep activity near the wall, i.e. in the region ≤10 wall units. All this results in increased wall normal velocity fluctuations in the viscous sublayer that may significantly impact heat and mass transfer rates. Estimates based on the data indicate an increase of ∼18% in heat transfer rates with only 5% increase in wall friction. |
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