Multi-Element Unstructured Analyses of Complex Valve Systems

Abstract

The safe and reliable operation of high pressure test stands for rocket engine and component testing places an increased emphasis on the performance of control valves and flow metering devices. In this paper, we will present a series of high fidelity computational analyses of systems ranging from cryogenic control valves and pressure regulator systems to cavitating venturis that are used to support rocket engine and component testing at NASA Stennis Space Center. A generalized multi-element framework with sub-models for grid adaption, grid movement and multi-phase flow dynamics has been used to carry out the simulations. Such a framework provides the flexibility of resolving the structural and functional complexities that are typically associated with valve-based high pressure feed systems and have been difficult to deal with traditional CFD methods. Our simulations revealed a rich variety of flow phenomena such as secondary flow patterns, hydrodynamic instabilities, fluctuating vapor pockets etc. In the paper, we will discuss performance losses related to cryogenic control valves, and provide insight into the physics of the dominant multi-phase fluid transport phenomena that are responsible for the "choking like" behavior in cryogenic control elements. Additionally, we will provide detailed analyses of the modal instability that is observed in the operation of the dome pressure regulator valve. Such instabilities are usually not localized and manifest themselves as a system wide phenomena leading to an undesirable chatter at high flow conditions.

A CFD analysis of the dynamics of a direct-operated safety relief valve mounted on a pressure vessel

“…Ahuja et al [6,8] presented a series of high fidelity computational simulations of control valves used in NASA testing. 3D multi-element framework with sub-models for grid adaption and multi-phase flow dynamics have been used to investigate the instability that results from valve operation.…”

“…From the 90's, with the development of computational methods, the computational analysis of the complex flows through valves have became more feasible thus leading to substantial research into the operation and design of SRVs [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. For example, Vu and Wang [1] investigated the complex three-dimensional flow field of an oxygen SRV during an incident with CFD (computational fluid dynamics) techniques.…”

Computational Modeling of Liquid and Gaseous Control Valves

“…Grids for complex 3D control valves are generated very efficiently by dissolving the seat region and inlet/discharge ducts by hexahedral and prismatic cells, and stitching them together with tetrahedral cells 4,5 . The grid connectivity is stored as an edgebased, cell-vertex data structure, where a dual volume is obtained for each vertex by defining surfaces that cut across edges coming to a node.…”

“…Work has previously been reported on modeling a high-pressure gas regulator valve 5 . Because of the high-speed flows which can occur in high-pressure gas valves, compressibility effects become important.…”

Transient Simulations of Valve Motion in Cryogenic Systems

“…These instabilities can couple with the valve motion and structural elements leading to undesirable "chatter" in the valve system. 1,2 Pressure fluctuations can also arise from valve operation (opening/closing) leading to the creation of cavitation zones in feed lines. These vapor pockets in turn can collapse and manifest themselves as dynamic instabilities by coupling with pressure oscillations from the system, and may result in fluctuating mass output from these valves.…”