Total pressure fluctuations and two-phase flow turbulence in self-aerated stepped chute flows

• Instantaneous total pressure measurements in clear-water and air-water flows.
• Metrology validated in air-water flows.
• Turbulence intensity in water phase derived from total pressure fluctuations.
• Water phase turbulence intensity smaller than interfacial turbulence intensity.
• Boundary layer development comparable to intermediate macro-roughness.

Current knowledge in high-velocity self-aerated flows continues to rely upon physical modelling. Herein a miniature total pressure probe was successfully used in both clear-water and air-water flow regions of high-velocity open channel flows on a steep stepped channel. The measurements were conducted in a large size facility (θ=45°, h=0.1 m, W=0.985 m) and they were complemented by detailed clear-water and air-water flow measurements using a Prandtl-Pitot tube and dual-tip phase-detection probe respectively in both developing and fully-developed flow regions for Reynolds numbers within 3.3×105 to 8.7×105. Upstream of the inception point of free-surface aeration, the clear-water developing flow was characterised by a developing turbulent boundary layer and an ideal-flow region above. The boundary layer flow presented large total pressure fluctuations and turbulence intensities, with distributions of turbulence intensity close to intermediate roughness flow data sets: i.e., intermediate between d-type and k-type. The total pressure measurements were validated in the highly-aerated turbulent shear region, since the total pressure predictions based upon simultaneously-measured void fraction and velocity data agreed well with experimental results recorded by the total pressure probe. The results demonstrated the suitability of miniature total pressure probe in both monophase and two-phase flows. Both interfacial and water phase turbulence intensities were recorded. Present findings indicated that the turbulence intensity in the water phase was smaller than the interfacial turbulence intensity.

Dimensionless distributions of total pressure, void fraction and turbulence intensity in the water phase of air-water fully-developed flow region of skimming flows - Flow conditions: dc/h=1.7, Re=8.7×105. (A) Dimensionless distributions of total pressure and void fraction in the air-water fully-developed flow region of skimming flows - Comparison between total pressure data Pt and estimated total pressure Pt, est based upon phase detection probe data, (B) Total pressure sensor turbulence intensity data Tup.Figure optionsDownload as PowerPoint slide