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Pumps and Turbines
Published in Henry Liu, Pipeline Engineering, 2017
Fluid coupling is a rotating machine whose casing contains both a pump impeller and a turbine runner of similar size and shape mounted next to each other on separate shafts for the purpose of smooth transmission of the torque from the impeller to the runner. The fluid contained in the coupling is usually an oil, which not only transmits the torque but also lubricates the machine and conducts and dissipates heat. It is the same device used in automatic transmissions in automobiles. When installed between a rotating pump and a rotating motor, the pump-side shaft of the coupling is connected directly to the motor or drive shaft, whereas the turbine (runner) side of the coupling is connected directly to the pump shaft. Use of such a device not only prevents fluctuations of the torque and speed in the drive shaft from being transmitted to the pump shaft, it also prevents the build-up of large torques in the motor (drive) shaft during start-up of pumps. The extra torque needed to accelerate the pump during start-up is minimized as the pump slowly picks up its speed during start-up with a fluid coupling. Note that soft couplings such as fluid coupling and eddy-current coupling are not necessary for starting up a centrifugal pump if the valve that controls the flow through the pump is completely closed during start-up. This is so because without flow going through the pump, only a small quantity of fluid is moved (circulated) within the pump casing when the centrifugal pump is on. The pump itself is now acting as a fluid coupling, limiting the torque that can be generated during start-up.
Fluid couplings and torque converters
Published in M.J. Nunney, Light and Heavy Vehicle Technology, 2007
The purpose of using a fluid coupling in a vehicle transmission system is generally to secure the following advantages: Absence of direct mechanical contact between the driving and driven members minimizes the transmission of shock and torsional vibration between the engine and the drive line.No positive disengagement or engagement of drive allows a smoother starting characteristic, this being particularly advantageous when restarting up a steep hill.Protects against harmful labouring of the engine at low speeds, since the fluid coupling will merely slip and allow the engine to increase speed when overloaded.
Transmission Fluid Properties’ Effects on Performance Characteristics of a Torque Converter: A Computational Study
Published in Tribology Transactions, 2021
Yang Yang, William W. Liou, Farrukh Qureshi, David J. Whitticar, Michael E. Huston
Hydraulic torque converters (HTCs) are an integral part of automatic and power shift transmissions and are used as a fluid coupling device between engine’s output shaft and transmission’s input shaft (1, 2). Functionally for a torque converter, torque is transmitted from engine to transmission through the fluid coupling until input and output shaft speeds approach one another and the shafts mechanically lock up when equipped with a lock-up clutch. It is estimated that nearly 30 million torque converters are used annually in passenger vehicles. Off-highway and construction equipment also use torque converters. Though there are many varying torque converter designs, the most common type consists of three elements, including turbine, stator, and impeller. Torque converter efficiency is important from the standpoint of managing parasitic losses. Additionally, a design parameter known as the k-factor has implications for the torque converter design and performance characteristics of the equipment.
A new 1D coupled hydrodynamic discrete element model for floating debris in violent shallow flows
Published in Journal of Hydraulic Research, 2020
Yan Xiong, Samantha Mahaffey, Qiuhua Liang, Mohamed Rouainia, Gang Wang
Numerical modelling is a prevalent research tool that has been explored to simulate the interaction between fluid flows and floating objects. This is usually achieved by coupling two different types of models. There are three types of coupling methods to depict the interaction, i.e. one-way solid-to-fluid coupling, one-way fluid-to-solid coupling, and two-way dynamic coupling (O’Brien, Zordan, & Hodgins, 2000). The one-way solid-to-fluid coupling approaches calculate the fluid dynamics with prescribed motion of the solids (Wu et al., 2014). The one-way fluid-to-solid coupling methods predict the movement of solids driven by a fluid flow without considering the feedback of the solids on the fluid. For example, Stockstill, Daly, and Hopkins (2009) developed a one-way fluid-to-solid coupled model using a finite-element shallow water hydrodynamic model and a discrete element method (DEM). After being validated against laboratory experiments, their model was used to simulate the movements of floating objects driven by shallow flow and regulated by navigational structures in a river channel. Since both types of one-way coupled models do not consider the feedback of the recipient phase to the driving phase, they are only applicable to certain cases where the dynamics of either the fluid or the solid phase is less predominant than the interaction between them (Wu et al., 2014) and the feedback of the recipient phase is negligible. Apparently, the one-way coupling approaches are not adequate in simulating the complex debris-enriched flow hydrodynamics induced by the aforementioned extreme natural hazard events.
Development and validation of a CFD based optimization procedure for the design of torque converter cascade
Published in Engineering Applications of Computational Fluid Mechanics, 2019
Cheng Liu, Changle Xiang, Qingdong Yan, Wei Wei, Cori Watson, Houston G. Wood
A torque converter is a fluid coupling device which transfers power through the interaction of moving fluids and cascades. Torque converters are wear-free and are capable of absorbing vibration from the input sources and providing torque amplification. Thus, torque converters are widely used in vehicle transmissions and industrial power transmissions. It consists of a pump, which is driven by a prime mover, a turbine, which is connect to the working machine and a stator, which is fixed to the transmission case (Liu, Liu, & Ma, 2015). The blade shape is highly twisted and the internal flow is highly turbulent, which makes the design of torque converters a complex procedure.