Title:	Highly resolved simulations of turbulence and cavitation during steady and transient operation of hydraulic machines
DNr:	SNIC 2021/6-342
Project Type:	SNIC Medium Storage
Principal Investigator:	Håkan Nilsson <hakan.nilsson@chalmers.se>
Affiliation:	Chalmers tekniska högskola
Duration:	2022-01-01 – 2023-01-01
Classification:	20306
Homepage:	http://www.chalmers.se/sv/personal/Sidor/hakan-nilsson.aspx
Keywords:

Abstract

This storage project is connected to Large compute-project SNIC 2021/3-10 The Large compute-project SNIC 2021/3-10 will provide computational resources for the following research areas: 1. Turbulence: Resolved simulations of high-Re flows in complex geometries (URANS, DES, LES). 2. Cavitation: A two-phase flow phenomenon requiring extreme mesh resolution, short time steps, and long real-time simulations. 3. Transients in hydraulic machines, such as shutdown and startup. 4. Machine learning algorithms for better understanding of flow physics in hydraulic machines. 5. Optimization of novel counter-rotating pump-turbines in transient operation. Three main applications will be investigated using computational fluid dynamics (CFD). Those are (1) transients in Kaplan and Francis water turbines, (2) transients in novel pump-turbines, and (3) cavitation modeling at off-design operation in water turbines. In all three applications, it is necessary to perform highly resolved CFD simulations of the flow, using hybrid/DES/LES turbulence modelling techniques. Such simulations are resource demanding already for simple applications. At the high Reynolds numbers and in the complex geometries of the present applications, it is much more demanding. We particularly need to study long real-time events and include both mesh rotation as well as mesh deformation due to changes in operating conditions. Cavitation is a two-phase flow phenomenon that involves phase change as the local pressure passes the vaporization pressure, and it requires highly resolved simulations both in time and space. We have, during many years, been part of the development and validation of the methods and models needed to do these kinds of simulations using the OpenFOAM open-source software, and all of the functionality to successfully do the studies are now in place. The aim of the present project is thus to produce highly detailed results of the flow under many operating conditions and operating sequences, including cavitation modeling. Storage requested through the present proposal: Due to the fact that we will be studying transients between different operating conditions, we need to save data at many time steps, in order to be able to post-process the results after finishing the simulations. I.e., this is not regular 'unsteady' simulations, but the conditions are also varying. We also need to install several versions of OpenFOAM and related software, which takes a lot of space and has many files.