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CURATOR
A pinboard by
Yu Qian

PhD Student, University of Alberta

PINBOARD SUMMARY

Measuring air flow in actual sewer system may be difficult and therefore CFD has its strength

I am interested in numerically modelling the air movement in sewer systems. The effect of pressure and wastewater drag were studied. The air movement in sewer networks was also successfully modeled. Currently, I am doing geyser events in storm sewer systems. The outcome of my studies provide the municipals some idea on odor control and flooding management city wide.

I contributed several publications in world top journals. Unfortunately the database of Sparrho does not include the American Society of Civil Engineering journals, and conference papers.

Following is a list of my publications:

Qian, Y., Zhu, D. Z., Zhang, W., Rajaratnam, N., Edwini-Bonsu, S., and Steffler, P. (2017). “Air Movement Induced by Water Flow with a Hydraulic Jump in Changing Slope Pipes.” Journal of Hydraulic Engineering, 143(4): 10.1061/(ASCE)HY.1943-7900.0001252.

Qian, Y., Zhu, D. Z., and Edwini-Bonsu, S. (2017). “Numerical Study on Potential Ways of Diminish Geysers in Storm Sewer Systems.” Journal of Hydraulic Engineering, ASCE, to be submitted.

Qian, Y., Zhu, D. Z., and Edwini-Bonsu, S. (2017). “Air Flow Modelling in a Prototype Sanitary Sewer System.” Journal of Environmental Engineering, ASCE, accepted.

Qian, Y., Zhu, D. Z., Rajaratnam, N. (2015). “Numerical Study on Air Movement in Steep Sewer Pipes.” IAHR World Congress Proceedings, 36th Congress, The Hague, The Netherland, 28 June – 3 July, 2015

Guo, S., Qian, Y., Zhu, D. Z., Zhang, W., and Edwini-Bonsu, S. (2017). “Effects of Drop Structures and Pump Station on Sewer Air Pressure and Hydrogen Sulfide: Field Investigation.” Journal of Environmental Engineering, ASCE, accepted.

Qian, Y., Guo, S., Zhu, D. Z., and Edwini-Bonsu, S. (2017). “Field Monitoring of Sewer Airspace Pressurization due to Dropshafts and a Pump Station.” Proceedings of 14th IWA/IAHR International Conference on Urban Drainage, Prague, Czech Republic, 10 – 15 September, 2017.

Azimi, A. H., Qian, Y., Zhu, D. Z., and Rajaratnam, N. (2015). "An experimental study of circular sand-water wall jets." International Journal of Multiphase Flow, 74: 34-44.

Ma, Y., Qian, Y., and Zhu, D. (2013) Effect of air core on the shape and discharge of the outflow through a bottom outlet. Theoretical and Applied Mechanics Letters, 3: 022003

9 ITEMS PINNED

Air-water flow characteristics in high-velocity free-surface flows with 50% void fraction

Abstract: High-velocity free-surface flows are complex two-phase flows and limited information is available about the interactions between air and water for void fractions of about 50%. Herein a detailed experimental study was conducted in the intermediate flow region (C ∼ 50%) on a stepped spillway and the microscopic air-water flow characteristics were investigated. The results showed differences in water and droplet chord times with comparatively larger number of air chord times (0-2 ms), and larger number of water chord times (2-6 ms). A monotonic decrease of particle chord modes was observed with increasing bubble count rates. Several characteristic time scales were identified based upon inter-particle arrival time analyses of characteristic chord time classes as well as spectral analyses of the instantaneous void fraction signal. Chord times of 3-5 ms appeared to be characteristic time scales of the intermediate flow region having similar time scales compared to the local correlation and integral turbulent time scales and to time scales associated with bubble break-up and turbulent velocity fluctuations. A further characteristic time scale of 100 ms was identified in a frequency analysis of instantaneous void fraction. This time scale was of the same order of magnitude as free-surface auto-correlation time scales suggesting that the air-water flow structure was affected by the free-surface fluctuations.

Pub.: 23 Jun '16, Pinned: 16 Aug '17

TOTAL PRESSURE FLUCTUATIONS AND TWO-PHASE FLOW TURBULENCE IN SELF-AERATED STEPPED CHUTE FLOWS

Abstract: 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.

Pub.: 13 Aug '16, Pinned: 16 Aug '17

Scale effects in microscopic air-water flow properties in high-velocity free-surface flows

Abstract: Experiments of high-velocity air-water flows were conducted on two scaled stepped spillways with step heights of h = 0.05 and 0.1 m to investigate scale effects in terms of air-water flow properties for a wide range of discharges in transition and skimming flows. The investigation comprised the complete range of macroscopic and microscopic two-phase flow properties including basic air-water flow parameters, interfacial turbulence properties, as well as cluster properties based upon the near-wake criterion and interparticle arrival time. For both undistorted Froude and Reynolds similitudes, the comparative analysis highlighted scale effects in terms of several gas-liquid flow properties, demonstrating that an extrapolation to full-scale prototype conditions may not be possible. These properties comprised the interfacial area, the turbulence properties and the particle sizes and grouping, affecting any scaling of air-water mass transfer processes. Other key air-water parameters were scaled accurately including the void fraction, interfacial velocity and flow bulking. The present investigation was the most comprehensive to date providing clear guidance on air-water flow properties which may be affected by scale effects. The present results may be also applicable to other types of air-water flows. However detailed testing of air-water flow properties at the prototype scale is needed for final confirmation.

Pub.: 16 Dec '16, Pinned: 16 Aug '17

Self-similarity and scale effects in physical modelling of hydraulic jump roller dynamics, air entrainment and turbulent scales

Abstract: A physical study of hydraulic jump is often undertaken using down-scaled Froude-similar models with Reynolds numbers much smaller than in prototype (e.g. spillway stilling basins). The potential viscous scale effects may affect a number of physical processes including turbulence development and air entrainment, thus challenging the extrapolation of laboratory data to the prediction of prototype conditions or justification of numerical modelling. This paper presents an experimental study of hydraulic jumps with a particular focus on the scale effects in terms of free-surface fluctuation and deformation, bubble advection and diffusion, bubble-turbulence interaction and turbulence dissipation. A broad range of free-surface, air–water flow and turbulence properties were measured systematically for Froude numbers from 3.8 to 10 and Reynolds numbers from 2.1 × 104 to 1.6 × 105. Based upon self-similarities in the longitudinal evolution of a number of characteristic flow properties, the analytical expressions of time-averaged roller surface profile, void fraction distribution and longitudinal velocity distribution were derived for given Froude number. The roller surface dynamics were found free of scale effects in terms of fluctuation amplitudes but the characteristic frequencies were scale-sensitive. While some air–water flow parameters such as bubble count rate, bubble chord time distribution and bubble grouping behaviour could only be correctly quantified at full-scale prototype conditions, the aeration level and turbulent scales might be estimated with satisfactory accuracy for engineering applications given a model Reynolds number no less than 4 × 10 to 6 × 104.

Pub.: 29 Jun '16, Pinned: 16 Aug '17

Coupling between free-surface fluctuations, velocity fluctuations and turbulent Reynolds stresses during the upstream propagation of positive surges, bores and compression waves

Abstract: In open channel, canals and rivers, a rapid increase in flow depth will induce a positive surge, also called bore or compression wave. The positive surge is a translating hydraulic jump. Herein new experiments were conducted in a large-size rectangular channel to characterise the unsteady turbulent properties, including the coupling between free-surface and velocity fluctuations. Experiments were repeated 25 times and the data analyses yielded the instantaneous median and instantaneous fluctuations of free-surface elevation, velocities and turbulent Reynolds stresses. The passage of the surge front was associated with large free-surface fluctuations, comparable to those observed in stationary hydraulic jumps, coupled with large instantaneous velocity fluctuations. The bore propagation was associated with large turbulent Reynolds stresses and instantaneous shear stress fluctuations, during the passage of the surge. A broad range of shear stress levels was observed underneath the bore front, with the probability density of the tangential stresses distributed normally and the normal stresses distributed in a skewed single-mode fashion. Maxima in normal and tangential stresses were observed shortly after the passage of a breaking bore roller toe. The maximum Reynolds stresses occurred after the occurrence of the maximum free-surface fluctuations, and this time lag implied some interaction between the free-surface fluctuations and shear stress fluctuations beneath the surge front, and possibly some causal effect. In open channel, canals and rivers, a rapid increase in flow depth will induce a positive surge, also called bore or compression wave. The positive surge is a translating hydraulic jump. Herein new experiments were conducted in a large-size rectangular channel to characterise the unsteady turbulent properties, including the coupling between free-surface and velocity fluctuations. Experiments were repeated 25 times and the data analyses yielded the instantaneous median and instantaneous fluctuations of free-surface elevation, velocities and turbulent Reynolds stresses. The passage of the surge front was associated with large free-surface fluctuations, comparable to those observed in stationary hydraulic jumps, coupled with large instantaneous velocity fluctuations. The bore propagation was associated with large turbulent Reynolds stresses and instantaneous shear stress fluctuations, during the passage of the surge. A broad range of shear stress levels was observed underneath the bore front, with the probability density of the tangential stresses distributed normally and the normal stresses distributed in a skewed single-mode fashion. Maxima in normal and tangential stresses were observed shortly after the passage of a breaking bore roller toe. The maximum Reynolds stresses occurred after the occurrence of the maximum free-surface fluctuations, and this time lag implied some interaction between the free-surface fluctuations and shear stress fluctuations beneath the surge front, and possibly some causal effect.

Pub.: 01 Aug '16, Pinned: 16 Aug '17