This study reports on an experimental investigation on laminar jets discharging from V-notched nozzles of different relative sharpness. Each nozzle consists of two smooth peaks and two sharp troughs and its sharpness is defined by the aspect ratio (AR) of the half ellipses which make up each half of the V-notch. Two ARs of AR=2 and 4 are used here to look at how changes in relative sharpness affect the vortex dynamics and quantifiable flow characteristics. Flow visualization results reveal the formation of coherent streamwise vortices at both peaks and troughs, as well as the bending of the large-scale vortex roll-ups. Digital particle-image velocimetry measurements reveal that peaks produce vortex roll-ups which are stronger than those associated with the troughs and that their strength difference increases with nozzle sharpness. Correspondingly, flow stresses show that the peaks and troughs tend to confer more significant effects upon the Reynolds normal stresses when nozzle sharpness increases, with Reynolds shear stresses remaining relatively invariant. Comparisons with an earlier study using an AR=1.5 nozzle show that depending on the nozzle sharpness, the large-scale vortex-bending behavior linked to axis switching can reverse in direction. Unlike the earlier study which produced vortex bending toward the upstream direction, the present sharper nozzles resulted in vortex bending in the downstream direction. Earlier formation of streamwise vortices at the troughs and associated vortex disconnection/reconnection processes are deduced to produce such a discrepancy and flow interpretations are presented for further clarifications.

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Digital particle image velocimetry was used to study hybrid inclined nozzles formed by combining flat-and inclined-sections, where the latter are designed based on the aspect-ratios (AR = 2 and 4) of half-ellipses. Results show that AR2 nozzle exhibits flow behaviour largely similar to inclined nozzles with inclined vortex roll-ups moving away from the nozzle centerline. In contrast, AR4 nozzle leads to significantly more intense near-field flow behaviour caused by the sharper junctions, which prevent similar movement of the vortex roll-ups. Streamwise vortices are also observed to form off the peaks of inclined-sections which produce wider jetsspreads along the inclined-sections due to associated lateral jet fluid ejection, though there is a limit to the jet-spread increment. Lastly, both nozzles produce higher turbulent stress levels over those of the conventional circular nozzle, and vortex roll-up vectoring leads to higher turbulent stresses for the AR2 nozzle along certain measurement planes.Keywords Jets · Indeterminate-origin nozzle · Inclined nozzle · Digital particle image velocimetry Abbreviations D Nozzle diameter (m) f Forcing frequency (Hz) U Mean jet exit velocity (m/s) u Mean streamwise velocity in x-direction (m/s) u Streamwise velocity fluctuations in x-direction (m/s) u rms Root-mean-square of velocity fluctuations (m/s) u mean Mean velocity magnitude, (u) 2 + (v) 2 , (m/s) 486 Flow Turbulence Combust (2009) 83:485-509 v Mean cross-stream velocity in y-direction (m/s) vCross-stream velocity fluctuations in y-direction (m/s) u u /U 2 Normalised streamwise normal stress u v /U 2 Normalised Reynolds shear stress v v /U 2 Normalised cross-stream normal stress wMean cross-stream velocity in z-direction (m/s) xStreamwise distance from nozzle mean height (m) yCross-stream distance along θ = π /2 plane (m) zCross-stream distance along θ = 0 plane (m) AR Aspect ratio px Pixel ReReynolds number, Re=UD/ν St Strouhal number, St=fD/U θ Angle of measurement plane (rad) νKinematic viscosity of water (m 2 /s)

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