Marco Geron

Comparison of Lagrangian and Eulerian Simulations of Slurry Flows in a Sudden Expansion

From a review of technical literature, it was not apparent if the Lagrangian or the Eulerian dispersed phase modeling approach was more valid to simulate dilute erosive slurry flow. In this study, both modeling approaches were employed and a comparative analysis of performances and accuracy between the two models was carried out. Due to an impossibility to define, for the Eulerian model already implemented in FLUENT , a set of boundary conditions consistent with the Lagrangian impulsive equations, an Eulerian dispersed phase model was integrated in the FLUENT code using subroutines and user-defined scalar equations. Numerical predictions obtained from the two different approaches for two-phase flow in a sudden expansion were compared with the measured data. Excellent agreement was attained between the predicted and observed fluid and particle velocity in the axial direction and for the kinetic energy. Erosion profiles in a sudden expansion computed using the Lagrangian scheme yielded good qualitative agreement with measured data and predicted a maximum impact angle of 29 deg at the fluid reattachment point. The Eulerian model was adversely affected by the reattachment of the fluid phase to the wall and the simulated erosion profiles were not in agreement with the Lagrangian or measured data. Furthermore, the Eulerian model under-predicted the Lagrangian impact angle at all locations except the reattachment point.

Combination of CFD and DOE to analyse solid particle erosion in elbows

Solid particle erosion is a major concern in the engineering industry, particularly where transport of slurry flow is involved. Such flow regimes are characteristic of those in alumina refinement plants. The entrainment of particulate matter, for example sand, in the Bayer liquor can cause severe erosion in pipe fittings, especially in those which redirect the flow. The considerable costs involved in the maintenance and replacement of these eroded components led to an interest in research into erosion prediction by numerical methods at Rusal Aughinish alumina refinery, Limerick, Ireland, and the University of Limerick. The first stage of this study focused on the use of computational fluid dynamics (CFD) to simulate solid particle erosion in elbows. Subsequently an analysis of the factors that affect erosion of elbows was performed using design of experiments (DOE) techniques. Combining CFD with DOE harnesses the computational power of CFD in the most efficient manner for prediction of elbow erosion. An analysis of the factors that affect the erosion of elbows was undertaken with the intention of producing an erosion prediction model.

Three Dimensional Features of Clustered Plug Nozzle Flows

The plug nozzle is one of the concepts proposed to improve the overall performance of large liquid rocket engines for launcher first stages. One of the aspects to be investigated is the three dimensional flow field generated by partitioning of the primary nozzle in modules. Three configurations with different size of the gap between two adjacent primary nozzles are selected and numerically simulated. Specific three-dimensional flow structures that take place on the plug are identified comparing the numerical solutions. The relationship between these structure and the skin friction distribution along the plug surface is also investigated. Finally, a performance analysis of the selected test cases based on the thrust coefficient evaluation is presented.

Transition between open and closed wake in 3D linear aerospike nozzles

Linear aerospike nozzles are envisaged as a possible device able to improve launcher engine performance. One of the most interesting properties of these nozzles is the possibility of a good integration with the vehicle. To improve the knowledge of the flow-field and performance of aerospike nozzles, they are studied numerically, with particular attention to the dierences between the basic two-dimensional nozzle, usually considered in the design phase, and the more realistic three-dimensional nozzle. The study considers dierent plug lengths and ambient pressures to assess the role of the linear plug side truncation on the base pressure behavior. Numerical tests are carried out at supersonic flight Mach number.

Performance analysis of an infinite array linear clustered plug nozzle

I N the challenge of realizing a new generation of space launchers, either single or two stage to orbit, an important role is played by the performance of the engine expansion system working in a varying pressure environment. In this framework a great interest has been devoted to the linear plug nozzle, which has been the subject of several studies in the last decade [1–6]. The plug nozzle is an external-expansion nozzle that yields self-adaptation of the exhaust jet to varying ambient pressure ratios, in a certain range of the launcher trajectory. This self-adapting capability allows high nozzle expansion ratios while avoiding the risks of flow separation that would exist in equivalent bell nozzles. The plug nozzle is made of a primary internal expansion nozzle, which is a conventional supersonic nozzle, and an external-expansion ramp, referred to as the plug surface. Most of the different engineering solutions proposed for plug nozzles have the following common feature: the primary expansion is made through a cluster of bell nozzles (or modules) exhausting onto a common linear plug surface [7–9]. The primary nozzle partitioning allows easier manufacturing, lower thermal loads, easier cooling and higher thrust vector capability. However, clustering causes additional performance losses due to three-dimensional flow inside the modules and to the interaction of jets exhausting from adjacent modules. For these reasons the three-dimensional features have to be studied in depth to better predict the engine performance and the expected mechanical and thermal loads for nominal operating conditions both at sea level and altitude and for differentially throttled modules as well. In fact, the thrust vectoring could be achieved by differential throttling of modules and, when thrust requirement is reduced in the final part of the ascent, some of the modules could be intentionally shut down. To this goal, the present paper studies by numerical simulation, the three-dimensional flowfield generated by themodules on a reference linear plug surface. The attention is focused on the effects of the three-dimensional flow features that take place when two different kind of modules are considered: the first module is obtained by dividing the reference two-dimensional primary nozzle by vertical walls and the second one is a full three-dimensional round-to-square nozzle. The performance analysis of these different module configurations allows weighing separately the role of clustering (i.e., just divide the primary nozzle into modules with infinitely thin flat walls) and the role of module design. A further subject of this study is the analysis of the effects produced by the shut down of a module of the cluster, for both module configurations. The analysis of the different configurations is made by comparing the thrust losses with the reference two-dimensional solution.

Analysis of a three-dimensional flow generated by a linear aerospike

Linear aerospike nozzles are envisaged as a possible means to improve launcher engine performance. One of the most interesting properties of these nozzles is the possibility of a good integration with the vehicle. To improve the knowledge of the flow-field and performance of aerospike nozzles, they are studied numerically, with particular attention to the differences between the basic two-dimensional nozzle, usually considered in the design phase, and the more realistic three-dimensional nozzle. The study considers also the effect of flight condition, which cannot be neglected because of the characteristic external expansion of aerospike nozzles.

Slot width augmentation in a slotted-wall transonic linear cascade wind tunnel

This paper was published as Proceedings of the 42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, USA, 5-8 January, 2004, pp. 1-11. It is also available from http://www.aiaa.org/content.cfm?pageid=298

Numerical Modelling of Heat Transfer in a Cavity due to Liquid Jet Impingement for Liquid Supported Stretch Blow Moulding

Impingement of a liquid jet in a polymer cavity has been modelled numerically in this study. Liquid supported stretch blow moulding is a nascent polymer forming process using liquid as the forming medium to produce plastic bottles. The process derives from the conventional stretch blow moulding process which uses compressed air to deform the preform. Heat transfer away from the preform greatly increases when a liquid instead of a gas is flowing over a solid; in the blow moulding process the temperature of the preform is tightly controlled to achieve optimum forming conditions. A model was developed with Computational Fluid Dynamics code ANSYS Fluent which allows the extent of heat transfer between the incoming liquid and the solid preform to be determined in the initial transient stage, where a liquid jet enters an air filled preform. With this data, an approximation of the extent of cooling through the preform wall can be determined.

A methodology for sensor modeling and placement optimization to support temperature monitoring

This paper presents a modeling and optimization approach for sensor placement in a building zone that supports reliable environment monitoring.