Boundary-layer resistances of artificial leaves in turbulent air II: Leaves inclined to the mean flow

The effect of turbulence on boundary-layer resistances to heat and water vapour transfer from leaves inclined to the mean airflow has been studied using heated square plates in a wind tunnel. Heat and water vapour transfer coefficients increased with streamwise turbulence intensity for all angles of inclination of the plates to the mean flow, and the increase was dependent on the ratio of the longitudinal integral length scale to the plate dimension. This dependence on the turbulence length scale probably results from a resonant interaction between the boundary layer on the plate and the turbulence in the approaching mean flow.The paper also presents results of experiments with heated plates having serrated leading edges and/or a transverse ridge on the surface, conducted in an attempt to understand the aerodynamic importance of morphological irregularities on the leaf surface. The irregularities studied here disturbed the boundary layer on the plate, and greatly increased heat transfer when the angle of inclination of the plates to the mean wind was small, but had little effect when the angle of inclination exceeded 40 °.