A Head Loss Pressure Boundary Condition for Hydraulic Systems

Abstract

Despite the increase in computational power of HPC clusters, it is in most cases not possible to include the entire hydraulic system when doing detailed numerical studies of the flow in one of the components in the system. The numerical models are still most often constrained to a small part of the system and the boundary conditions may in many cases be difficult to specify. The headLossPressure boundary condition is developed in the present work for the OpenFOAM open-source CFD code to include the main effects caused by a large hydraulic system onto a component in the system. The main motivation is to provide a boundary condition for hydraulic systems where known properties are specified by the user and unknown properties are calculated. This paper is a guide to the developed headLossPressure boundary condition. It is based on the extended Bernoulli equation to calculate the kinematic pressure on the patch. An arbitrary number of minor and friction losses are considered to describe the system in terms of head losses. The boundary condition also provides the opportunity to specify the head in relation to a reference elevation. System changes during operations are modelled through Function1 variables, which enables time-varying inputs. The developments are validated against experimental test data, where the varying head between two free surfaces and a valve closing and opening sequence are modelled with the boundary condition. The main effects of the system are well captured by the headLossPressure boundary condition. It is thus a useful and trustworthy boundary condition for incompressible hydraulic system simulations.

System model development and numerical simulation of low-head pumped hydro storage

“…The comparison is based on the results of the high-fidelity model. The methodology and boundaries used for the CFD simulations are described in further detail by Fahlbeck et al (2021) and Fahlbeck et al (2022a).…”

Energy harvesting from water streaming at charged surface

“…𝑣 2 [71][72][73], where 𝑓, 𝐿, 𝐷 ℎ , and 𝑣 𝑣 are the friction loss coefficient, channel length, hydraulic diameter, and viscous flow velocity, respectively.…”

“… $$$$\begin{equation}\frac{{{p_i}}}{\rho } + \frac{{v_i^2}}{2} + {\mathrm{\;}}\Delta {\mathrm{\;}}{h_f} = {\mathrm{\;constant}}\end{equation}$$$$where $${p_i}$$,ρ, and $${v_i}$$ are pressure, liquid density, and velocity, respectively. The head loss can be expressed as $$\Delta \;{h_f} = \;f( {L/{D_h}} )\frac{{v_v^2}}{2}$$ [71–73], where f , L , $${D_h}$$, and $${v_v}$$ are the friction loss coefficient, channel length, hydraulic diameter, and viscous flow velocity, respectively.…”

Evaluation of startup time for a model contra-rotating pump-turbine in pump-mode

“…The flow rate is thus part of the solution. The inlet and outlet boundary conditions for pressure is handled with the novel headLossPressure boundary condition developed by Fahlbeck et al [21]. This special boundary condition allows the user to specify the head of the system and it also considers head losses up-and downstream of the computational domain.…”