Reply to the “Discussion by B.S. Pani on ‘Hydraulic characteristics of turbulent circular jets under surface confinement’ by F. Riyaz and Z. Ahmad (2014)”

This paper replies to the Discussion of Hydraulic characteristics of turbulent circular jets under surface confinement; B.S. Pani (ISH Journal of Hydraulic Engineering, 16th Jan 2014, vol. 20, 222–229). The authors would like to thank the discusser on his keen interest in the paper and for raising pertinent points for discussion. Experiments have been performed in a tank of limited length i.e. x/D = 50 and high Reynolds numbers; therefore, the effect of the front wall of the tank on the hydraulic characteristics of the jet under surface confinement cannot be ignored as pointed out by the discusser. Figures 3(a) and (b) show that measured Ue/Uc for H1/D = 10 matches well with the computed value using Lee et al. (2011) for jet velocities Ue = 4.25 m/s and Ue = 7.0 m/s, respectively, while Figure 3(c) shows that the measured value differs with computed for higher velocity Ue = 8.5 m/s and x/D = 25. It may be concluded that for jet velocities 4.25 and 7 m/s with little surface confinement i.e. H1/D = 10, the effect of front wall is negligible; however, it is noticeable for higher velocity 8.5 m/s. The effect of front wall shall be higher under strong surface confinement due to modest decay in the centerline velocity. In compliance to the findings of Shinneeb et al. (2011), in this experimental work also, the deflection of the jet was noticed towards the surface. The deflection was higher under strong surface confinement. It is obvious that ratio of jet velocity at x = 0 and velocity of jet at any distance x dips downward with surface confinement; however, in the Figures 3 (a)–(c), the ratio of jet velocity at x = 0 and centerline velocity at y = 0 for all values of x is plotted against x/D. In view of upward deflection of jet from centreline (y = 0), deflection of Ue/(Uc at y = 0) from straight line in an upward direction is obvious. Normalization of y with H has extensively been used in the literature (Shinneeb et al. 2011). In this paper also, same normalization has been adopted in view of studying distortion in symmetry in velocity profile due to the surface confinement. Methodology for the computation of discharge and energy fluxes is mentioned herein for better understanding. For calculating discharge flux and kinetic energy in surface confined jet at any section in axial direction, vertical section was divided into a number of small strips of radius r and thickness dr and each strip was divided into eight parts, so that the area of each part is equal to ð2prdrÞ=8 (Figure A1). The velocities on the center of each strip on the horizontal and vertical plane were obtained from the normalized velocity profiles. The velocities between vertical and horizontal axes were obtained by linear interpolation. The average velocity U in each segment was computed by taking the arithmetic mean of two velocities at both the ends of the segment. The flux entrainment and kinetic energy through small area dA is given by UdA and 0:5q U 3dA, respectively. The total discharge flux and kinetic energy through the section is given by Pn i1⁄41 UidAi and Pn i1⁄41 0:5q U 3 i dAi. , respectively, where n = number of the segments.