Numerical Analysis of Axisymmetric Nozzle Aerodynamic Characteristics

Method of CFD is used to simulate flow fields for a certain Axisymmetric nozzle, The paper describes the grid adaption, boundary conditions determination as well as RNG model application, and analyzes the nozzle aerodynamic characteristics. The numerical results match well with test data.

Parallel Mesh Adaptive Techniques Illustrated with Complex Compressible Flow Simulations

The aim of this paper is to discuss efficient adaptive parallel solution techniques on unstructured 2D and 3D meshes. We concentrate on the aspect of parallel a posteriori mesh adaptation. One of the main advantages of unstructured grids is their capability to adapt dynamically by localised refinement and derefinement during the calculation to enhance the solution accuracy and to optimise the computational time. Grid adaption also involves optimisation of the grid quality, which will be described here for both structural and geometrical optimisation.

Multi-Element Unstructured Analyses of Complex Valve Systems

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 submodels 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 using traditional computational fluid dynamics 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 a 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.

Algebraic method for efficient adaption of structured grids to fluctuating geometries

An efficient method for adaption of a structured grid to fluctuating turbine blade geometry is presented based on an algebraic algorithm. The objective of the application of this method is to analyse the aerodynamic, thermal and rotational load of rotating and cooled blades with a conjugate approach. The grid adaption method is validated with two test cases by using a simple deformation model considering the blade as a torsion spring. This model ensures a strong coupling between aerodynamic load and deformation of the blades. Thus, the stability of the numerical code can be analysed. The calculations show that convergence for the blade deformation is reached very soon. Even for great blade deformation the algebraic grid adaption method generates no negative cell volumes although this cannot be guaranteed by an algebraic algorithm.

Simulations of Unsteady Valve Systems

The safe and reliable operation of industrial facilities and high pressure test stands for engine and component testing is largely dependent on the smooth performance of control valves. However, such valves frequently experience pressure oscillations from hydrodynamic instabilities, cavitation and unsteady valve operation. In this paper, we present a series of high fidelity computational simulations of control valves primarily to understand the physics associated with the dominant instability modes. A generalized multi-element framework with sub-models for grid adaption, grid movement and multi-phase flow dynamics was used to carry out the simulations. We discuss the methodology in detail with the example of transient analyses of a gaseous hydrogen control valve and capture the fluid dynamic instability that results from valve operation. Additionally, we provide detailed analyses of a modal instability that is observed in the operation of a pressure regulator valve. In both cases, the instabilities are not localized and manifest themselves as a system wide phenomena leading to oscillations in mass flow and/or undesirable chatter.