Uwe Iben

Cavitation in Hydraulic Tools Based on Thermodynamic Properties of Liquid and Gas

The simulation of cavitation phenomena plays an important role for development of modern hydraulic tools and injection systems. Cavitation leads to a reduction of mass flow and influences the wave motion in hydraulic components significantly. The article deals with the simulation of a homogeneous cavitation model based on thermodynamic properties of the liquid and steam to understand basic physical phenomena

Modeling of Cavitation

The paper deals with the study of source terms for Euler and Navier-Stokes equations which describe cavitation phenomena in one- and three-dimensional flow. Cavitation occurs in many technical applications, such as injectors, throttles and pumps. The modeling of cavitation is a challenge due to the complex structure of the cavitation process and the difficult numerical realization. The main problem is to simulate one- or three-dimensional flow in order to predict the material of cavitation erosion or to determine the mass flow which will be limited if cavitation occurs in a throttle.

Toward a Discontinuous Galerkin Fluid Dynamics Framework for Industrial Applications

For many years, discontinuous Galerkin (DG) methods have been proving their value as highly efficient, very well scalable high-order methods for computational fluid dynamics (CFD) calculations. However, they have so far mainly been applied in the academic environment and the step toward an application in industry is still waited for. In this article, we report on our project that aims at creating a comprehensive CFD software that makes highly resolved unsteady industrial DG calculations an option. First, our focus lies on the adaptation of the solver itself to industrial problems and the optimization of the parallelization efficiency. Second, we present a visualization tool specifically tailored to the properties of DG data that will be combined with the solver to obtain an in-situ visualization strategy within our project in the near future.

Dynamic Load Balancing for the Parallel Simulation of Cavitating Flows

This paper deals with the parallel numerical simulation of cavitating flows. The governing equations are the compressible, time dependent Euler equations for a homogeneous two-phase mixture. These equations are solved by an explicit finite volume approach. In opposite to the ideal gas, after each time step fluid properties, namely pressure and temperature, must be obtained iteratively for each cell. This is the most time consuming part, particularly if cavitation occurs. For this reason the algorithms has been parallelized by domain decomposition. In case where different sizes of cavitated regions occur on the different processes a huge load imbalance problem arises. In this paper a new dynamic load balancing algorithm is presented, which solves this problem efficiently.

Air release measurements of V-oil 1404 downstream of a micro orifice at choked flow conditions

This study presents measurements on air release of V-oil 1404 in the back flow of a micro orifice at choked flow conditions using a shadowgraph imaging method. The released air was determined at three positions downstream of the orifice for different pressure conditions. It was found that more than 23% of the initially dissolved air is released and appears downstream of the orifice in the form of bubbles.

Parallel Simulation of Cavitated Flows in High Pressure Systems

Publisher Summary This chapter discusses the parallel numerical simulation of cavitating flows. The governing equations are the compressible, time dependent Euler equations for a homogeneous two-phase mixture. The equations of state for the density and internal energy are more complicated than the ideal gas. These equations are solved by an explicit finite volume approach. After each time step fluid properties— namely, pressure and temperature, must be obtained iteratively for each cell. The iteration process takes much time, particularly, if in the cell cavitation occurs. For this reason, the algorithm has been parallelized by domain decomposition. In case where different sizes of cavitated regions occur on the different processes, a huge load imbalance problem arises. This chapter discusses a new dynamic load balancing algorithm, which solves the problem efficiently. In many industrial applications, cavitation occurs and cannot be calculated detailed in a proper response time on a single processor computer. In order to reduce this time, the use of parallel computing architectures is necessary. Nevertheless, the parallel algorithm has to deal with load imbalance introduced by the cavities. The most time consuming part of the algorithm is the iterative calculation of pressure and temperature. A new load balancing algorithm has been developed, in which not cells, but the work done on the cells during determination of pressure and temperature, is redistributed across processors.

High-Pressure Real-Gas Jet and Throttle Flow as a Simplified Gas Injector Model Using a Discontinuous Galerkin Method

Industrial devices such as gas injectors for automotive combustion engines operate at ever-increasing pressures and already today reach regimes beyond the ideal-gas approximation. Numerical simulations are an important part of the design process for such components. In this paper, we present a case study with a computational fluid dynamics code based on the discontinuous Galerkin spectral element method with a real-gas equation of state. We assess a high-pressure throttle and jet flow as a basic model of a gas injector. We apply a shock-capturing method to achieve a robust simulation, and a newly developed method to maintain high efficiency despite load imbalances introduced by the shock capturing. The results indicate a dynamic mass flow rate at different pressure ratios between the inlet and outlet.

A PATH-CONSERVATIVE OSHER-TYPE SCHEME FOR AXIALLY SYMMETRIC COMPRESSIBLE FLOWS IN FLEXIBLE TUBES

Abstract. In industrial applications there exist numerous hydraulic devices, as for example the fuel injection system in modern combustion engines, or hydraulic braking systems. These devices become more and more complex, and also the requirements concerning their efficiency are continuously increasing. Therefore, it is necessary to understand these systems well in order to optimize them already at the design stage. For that purpose, it is important to have a numerical simulation tool available that is able to calculate a solution for a given configuration quickly and accurately. In hydraulic devices, the different components, like pumps, valves or vessels, are usually connected via flexible tubes. Thus, the relevant physical effects of such compliant tubes must be considered in the numerical simulation, especially at high frequencies. In typical industrial applications, pressures can reach several thousand bar, hence the flow has to be usually considered as compressible, and at the same time also the visco-elastic behavior of the tube wall needs to be properly accounted for. Then, a suitable numerical method needs to be developed in order to solve the resulting partial differential equations (PDE) of this coupled fluid-structure interaction (FSI) problem accurately and efficiently. In our talk, the equations of an axially symmetric flow of a compressible barotropic fluid are considered for flows through flexible elastic and visco-elastic tubes, so that the dominant physical effects can be reproduced according to the composition of the tube wall. To calculate the numerical solution of the derived PDE, a path-conservative Osher-type solver the so-called Dumbser-Osher-Toro (DOT)is applied. This solver can deal with hyperbolic conservation laws that may also contain non-conservative products. To validate the proposed mathematical model and the numerical scheme, the numerical solutions are compared with analytical results derived in the frequency domain, as well as with experimental measurements. In both cases, the proposed path-conservative finite volume scheme based on the DOT Riemann solver produces very good results.

Second Order Methods for the Simulation of Pressure Waves and Cavitation of Water

The simulation of pressure waves plays an important role in the development of modern hydraulic tools. Due to its strong influence on the speed of sound cavitation has a great influence on this nonlinear wave propagation. In this presentation we analyze some second order methods used for the simulation of these phenomena. In particular we show that some in the context of gas dynamics well known methods refuse to perform the desired simulations while others give reliable results.

Simulation of Cavitation in Thermodynamic Equilibrium

A method for the numerical simulation of cavitation phenomena is described. Thereby, a homogeneous cavitation model based on a thermodynamic equilibrium model of liquid and steam is considered. Besides a brief introduction into the mathematical model described in [1] we focus on the discretization tech- nique. The ability of the scheme is proven by numerical experiments.