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Air bubble entrainment is a phenomenon that can significantly reduce the efficiency of liquid motion in piping systems. In the present study, the bubble formation mechanism in a globe valve with 90% water fraction flow is explained by visualization study and pressure oscillation analysis. The shadowgraph imaging technique is applied to illustrate the unsteady flow inside the transparent valve. This helps to study the effect of bubbles induced by the globe valve on pressure distribution and valve flow coefficient. International Society of Automation (ISA) recommends locations for measuring pressure drop of the valve to determine its flow coefficient. This paper presents the comparison of the pressures at different locations along with the upstream and the downstream of the valve with the values at recommended positions by the ISA standard. The results show that in partially filled pipe flow, the discrepancies in pressure between different measurement locations in the valve downstream are significant at valve openings less than 30%. The aerated flow induces the oscillation in pressure and flow rate, which leads to the fluctuation in the flow coefficient of the valve. The flow coefficients have a linear relationship with the Reynolds number. For the same increase of Reynolds number, the flow coefficients grow faster with larger valve openings and level off at the opening of 50%.

Spillways of large and small dams experience flow conditions that exceed the capabilities of common water surface profile computer programs. Unique channel geometries, steep slopes, and streamline curvature demand rigorous mathematics, while phenomena associated with aerated flow and potential cavitation require special analyses, especially for stepped chutes. SpillwayPro is a generalized, energy-based, water surface profile calculation tool for both smooth and stepped chutes that integrates cavitation analysis and aerated flow effects, with separate modules supporting aerator design and the development of optimized structure profiles that meet cavitation parameter objectives. Simultaneous calculation of smooth and stepped-chute flow profiles enables the rapid assessment of the energy dissipation benefits of steps, as well as their unique aerated flow and cavitation issues. SpillwayPro’s technical basis is presented, and its results are compared to the data from prototype case studies and empirical methods developed from large-scale laboratory studies. SpillwayPro’s fundamental energy-based methods are useful for cases that differ from idealized empirical approaches and would benefit from a more rapid analysis than can be accomplished with physical or computational fluid dynamics (CFD) modeling.

The operation of stepped spillways is limited by a range of discharges due to the risk of occurrence of the cavitation phenomenon and erosion on its steps. Since there is a demand for spillways with the possibility of overflow of greater discharges, the designs seek to increase the air concentration of the flow, which can occur through the installation of piers in the spillway in order to protect the structure from the above mentioned damage. The aim of this work is to analyze flow characteristics and extreme minimum and maximum pressures with non-exceedance probability of 0.1% and 99.9% acting next to the step edges of the spillway with aeration induced by piers through an experimental analysis in a physical model. Based on the results obtained, flow behavior was defined and equations for predicting the extreme pressures that occur along the stepped spillway with aeration induced by piers were proposed. RESUMO Vertedouros em degraus têm sua operação limitada a faixas de vazões devido ao risco de ocorrência do fenômeno de cavitação e erosão em seus degraus. Como há demanda por vertedouros com possibilidade de extravasamento de maiores vazões, procura-se aumentar a concentração de ar do escoamento, que pode ocorrer através da instalação de pilares no vertedouro, para assim proteger a estrutura contra os referidos danos. O objetivo deste trabalho é avaliar as características do escoamento e as pressões extremas mínimas e máximas com probabilidade de 0,1% e 99,9% de não-excedência, atuantes nas quinas dos degraus do vertedouro com aeração induzida por pilares, através da análise experimental em um modelo físico. Baseado nos resultados obtidos foi definido o comportamento do escoamento e foram propostas equações de previsão das pressões extremas que ocorrem ao longo do vertedouro em degraus com aeração induzida por pilares.

Circular drop manholes are widely implemented for steep catchments in urban drainage networks. Poor downstream hydraulic transition processes of a manhole system, i.e., the formation of hydraulic jump near the outlet entrance, and the sudden transition from free surface to pressurized flow with bursts of air in the outflow pipe can severely constraint the capacity of water conveyance. In this paper, we defined four basic hydraulic stages that indicate where hydraulic transition processes begin and end. The measurements of typical manhole models with different drop heights were conducted under different inflow and outflow conditions. Three types of transition processes covering all flow patterns have resulted into a graphical visualization by analyzing two pairs of dimensionless parameters. The flow inside a circular drop manhole was considered to reach its discharge capacity when the abrupt drop of manhole water level is visible in the fully aerated flow pattern. Four empirical equations revealing the water level filling ratio and discharge efficiency at different hydraulic stages were also presented for further predictions of choking risks.

In this thesis, the results of a numerical modeling study that addresses the skimming flow properties in flat slope stepped channels, are presented and analyzed. Experimental data of mean flow velocity profiles from Hunt and Kadavy's physical model was used for the calibration of the results obtained with a numerical model performed with the commercial CFD tool: Ansys Fluent. SST k-omega was selected for turbulence modeling and Mixture model for the free surface tracking process, but as the flow aeration downstream the inception point wasn't captured by the mentioned models, a "data adjustment procedure" was proposed to be able to compare the experimental data from measuring stations with air entrance, with the numerical results. This work presents a hydrodynamical diagnosis addressing the relations between the mean flow velocity, static pressure, turbulent kinetic energy production and viscous dissipation rates along the skimming flow domain. Additional runs with wall roughness, riser height (h) and tread length (l) variations were performed to conclude about the effects in the mentioned hydrodynamical variables. Resumen: En esta tesis se presentan y analizan los resultados de un estudio de modelación numérica que aborda las propiedades del flujo rasante en canales escalonados de baja pendiente. Los datos experimentales de los perfiles de velocidad del flujo medio del modelo físico de Hunt y Kadavy, se usaron para la calibración de los resultados obtenidos con un modelo numérico realizado con la herramienta comercial CFD: Ansys Fluent. SST k-omega fue seleccionado para el modelado de la turbulencia y el modelo "Mixture" para el proceso de rastreo de la superficie libre, pero como la aireación de flujo aguas abajo del punto de incepción no fue capturada por los modelos mencionados, se realizó un "procedimiento de ajuste de datos" para poder comparar la información experimental de las estaciones de medición con entrada de aire, con los resultados numéricos. Este trabajo presenta un diagnóstico hidrodinámico que aborda las relaciones entre la velocidad, la presión estática y las tasas de producción y disipación viscosa de la energía cinética turbulenta del flujo medio, en todo el dominio del flujo rasante. Se llevaron a cabo corridas adicionales con variaciones en la rugosidad de la pared, la altura de la contrahuella (h) y la longitud de la huella (l) para concluir acerca de los efectos en las variables hidrodinámicas mencionadas. Maestría

There is a lack of knowledge on the air concentration distribution in plunge pools affected by aerated jets. A set of physical experiments was performed on vertical submerged aerated jet flows impinging a plunge pool. The air concentration distribution in the plunge pool was analyzed under different inflow air concentrations, flow velocities, and discharge rate conditions. The experimental results show that the air concentration distribution follows a power-law along the jet axis, and it is independent of the initial flow conditions. A new hypothetical analysis model was proposed for air diffusion in the plunge pool, that is, the air concentration distribution in the plunge pool is superposed by the lateral diffusion of three stages of the aerated jet motion. A set of formulas was proposed to predict the air concentration distribution in the plunge pool, the results of which showed good agreement with the experimental data.

Setting aeration facilities on the discharge structure in the dam to make the gas in the flow, is a common used method to reduce erosion damage to the building today. Based on the feature of the discharge structure and considering the types of the ventilation facilities and air-intake system, this paper simplified a model for project to analyze and established the corresponding mathematical model. With ICEM/CFD software the finite element model was generated. Using the commercial software FLUENT to do the flow state analysis, it obtained the velocity of the aerated flow and the pressure distribution. On the basis of the simulation of the single characteristic diameter bubble flow, it gave a contrast and analysis to the range of application and the differences of accuracy between the SIMPLE and PISO methods.