Q2. What was the effect of the bubbles on the flow?
Once the entrained bubbles were advected into regions of lesser shear, bubble coalescence led to the formation of larger air bubbles which were driven by buoyancytowards the free-surface.
Q3. What is the entrainment of air bubbles in skimming flows?
In skimming flows, air bubble entrainment takes place in the form of some interfacial aeration, and the entrained bubbles are advected in a boundary layer flow.
Q4. What is the function of the free surface?
With any ultrasonic displacement meter, the signal output is a function of the strength of the acoustic signal reflected by the‘‘free-surface”.
Q5. What was the calibration technique used for the displacement probes?
The ultrasonic displacement probes were calibrated with clearwater at rest against pointer gauge measurements for a range of water depths shortly before each experiment.
Q6. What type of probe was used for the air–water flow properties?
The air–water flow properties were measured with either two single type conductivity probes (£ = 0.35 mm) or a double-tip conductivity probe (£ = 0.25 mm, Dx = 7.0 mm).
Q7. What is the reason for the large fluctuations in free-surface elevations?
These large fluctuations in free-surface elevations reflected the unsteady, dynamic nature of the hydraulic jump, caused possibly by the production, break up and pairing of macro-scale turbulent vortices in the developing shear layer.
Q8. What is the theory of the advective diffusion equation for air bubbles?
It is believed to derive from the high levels of turbulent shear stresses in the air–water shear layer that break up the entrained air bubbles into finer air entities.
Q9. What was the effect of the turbulent time scale on the void fraction and bubble count rate?
The experimental observations showed systematically that the maximum void fraction Cmax and maximum bubble count rate Fmax were functions of the inflow Froude number Fr1, of the inflow Reynolds number Re and of the streamwise position (x x1)/d1.
Q10. What functions were used to analyse the signals?
When two probe sensors were simultaneously sampled, the signals were analysed in terms of the auto-correlation and cross-correlation functions Rxx and Rxz, respectively (Fig. 2).
Q11. What was the trend of the velocity distributions in the hydraulic jump?
In the present study, the distributions of interfacial velocity showed a decreasing velocity with increasing distance from the invert, while the magnitude of the velocity decreased with increasing distance from the jump toe at a given elevation (Fig. 8A).
Q12. What is the void fraction and bubble count rate in hydraulic jumps?
In hydraulic jumps with partially-developed inflow conditions, the void fraction and bubble count rate profiles showed consistently two distinct regions: (a) the turbulent shear region and (b) the upper region (e.g. Figs. 5 and 6).
Q13. what is the normalized cross-correlation function of the reference probe signal?
Rxz ds ð5Þwhere s is the time lag, Rxx is the normalized auto-correlation function of the reference probe signal, and Rxz is the normalized cross-Fig.