Reaction in a scalar mixing layer in grid-generated turbulence is studied experimentally by doping half of the flow with nitric oxide and the other half with ozone. The flow conditions and concentrations are such that the chemical reaction is passive and the flow and chemical timescales are of the same order. Conserved scalar theory for such flows is outlined and further developed; it is used as a basis for presentation of the experimental results. Continuous measurements of concentration are limited in their spatial and temporal resolution but capture sufficient of their spectra for adequate second-order correlations to be made. Two components of velocity have been measured simultaneously with hot-wire anemometry. Conserved scalar mixing results, deduced from reacting and non-reacting measurements of concentration, show the independence of concentration level and concentration ratio expected for passive reacting flow. The results are subject to several limitations due to the necessary experimental compromises, but they agree generally with measurements made in thermal mixing layers. Reactive scalar statistics are consistent with the realizability constraints obtainable from conserved scalar theory where such constraints apply, and otherwise are generally found to lie between the conserved scalar theory limits for frozen and very fast chemistry. It is suggested that Toor's (1969) closure for the mean chemical reaction rate could be improved by interpolating between the frozen and equilibrium values for the covariance. The turbulent fluxes of the reactive scalars are found to approximately obey the gradient model but the value of the diffusivity is found to depend on the Damköhler number.

The effect of wall suction on the organized motion of a tubulent boundary layer is examined experimentally both in a wind tunnel and in a water tunnel. In the windtunnel boundary layer, which developed over a slighly heated surface, temperature fluctuations were simultaneously obtained at several points, aligned in either the x (streamwise) or y (normal to the wall) direction. The temperature traces reveal the existence of two spatially coherent events, characterized either by a sudden decrease (cooling) or by a sudden increase (heating) of temperature. Estimates are presented for the average convection velocity, and average frequency of these events. The average convection velocity of ‘coolings’ is about 15% larger than that of ‘heatings’, the velocity of both events exhibiting an important local maximum in the buffer region. Near the wall, the convection velocity of both events is increased slightly by suction while their average frequency is reduced by suction. Away from the wall, the average inclination of ‘coolings’ and ‘heatings’ is about 40° without suction; suction does not alter the inclination of ‘coolings’ but increases that of ‘heatings’ to about 50°. Visualizations in the water tunnel indicate that suction increases the stability and the longitudinal coherence of low-speed streaks. They also show that suction reduces the average frequency of dye ejections into the outer layer.

The three components of the average temperature dissipation have been measured using a pair of parallel cold wires in an approximately self-preserving turbulent boundary layer. The mean square value of θ,x the temperature derivative in the longitudinal direction, is determined mainly by the use of Taylor's hypothesis, following direct verification of this hypothesis at a few locations in the flow. Mean square values of θ,y and θ,z, the temperature derivatives in directions normal to the flow, were estimated mainly from the curvature of spatial temperature autocorrelations. In the outer layer, the measurements indicate that $\overline{\theta^2}_{,z} > \overline{\theta^2}_{,y} > \overline{\theta^2}_{,x}$, and the resulting distribution for dissipation leads to a good closure of the $\frac{1}{2}\overline{\theta^2}$ budget. In the near-wall region the measurements indicate that $\overline{\theta^2}_{,y} > \overline{\theta^2}_{,z} > \overline{\theta^2}_{,x}$. The ratios $\overline{\theta^2}_{,y}/\overline{\theta^2}_{,x} $ and $\overline{\theta^2}_{,z}/\overline{\theta^2}_{,x}$ are as large as 13 and 7 respectively at y+ = 12, underlining the strong anisotropy in this region. The behaviour of the turbulent diffusion, estimated by difference, provides reasonable support for the accuracy of the near-wall temperature-dissipation measurements. Using existing data of near-wall distributions of the turbulent energy and of its dissipation rate, the timescale for the turbulent-energy dissipation is found to be approximately equal to that for the temperature dissipation.

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