Overview of Combustion Instabilities in Liquid-Propellant Rocket Engines

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An efficient surrogate model for emulation and physics extraction of large eddy simulations

In the quest for advanced propulsion and power-generation systems, high-fidelity simulations are too computationally expensive to survey the desired design space, and a new design methodology is needed that combines engineering physics, computer simulations and statistical modeling. In this paper, we propose a new surrogate model that provides efficient prediction and uncertainty quantification of turbulent flows in swirl injectors with varying geometries, devices commonly used in many engineering applications. The novelty of the proposed method lies in the incorporation of known physical properties of the fluid flow as {simplifying assumptions} for the statistical model. In view of the massive simulation data at hand, which is on the order of hundreds of gigabytes, these assumptions allow for accurate flow predictions in around an hour of computation time. To contrast, existing flow emulators which forgo such simplications may require more computation time for training and prediction than is needed for conducting the simulation itself. Moreover, by accounting for coupling mechanisms between flow variables, the proposed model can jointly reduce prediction uncertainty and extract useful flow physics, which can then be used to guide further investigations.Comment: Submitted to JASA A&C

Open-source development experiences in scientific software: the HANDE quantum Monte Carlo project

The HANDE quantum Monte Carlo project offers accessible stochastic algorithms for general use for scientists in the field of quantum chemistry. HANDE is an ambitious and general high-performance code developed by a geographically-dispersed team with a variety of backgrounds in computational science. In the course of preparing a public, open-source release, we have taken this opportunity to step back and look at what we have done and what we hope to do in the future. We pay particular attention to development processes, the approach taken to train students joining the project, and how a flat hierarchical structure aids communicationComment: 6 pages. Submission to WSSSPE

An Approach to Improved Credibility of CFD Simulations for Rocket Injector Design

Computational fluid dynamics (CFD) has the potential to improve the historical rocket injector design process by simulating the sensitivity of performance and injector-driven thermal environments to. the details of the injector geometry and key operational parameters. Methodical verification and validation efforts on a range of coaxial injector elements have shown the current production CFD capability must be improved in order to quantitatively impact the injector design process.. This paper documents the status of an effort to understand and compare the predictive capabilities and resource requirements of a range of CFD methodologies on a set of model problem injectors. Preliminary results from a steady Reynolds-Average Navier-Stokes (RANS), an unsteady Reynolds-Average Navier Stokes (URANS) and three different Large Eddy Simulation (LES) techniques used to model a single element coaxial injector using gaseous oxygen and gaseous hydrogen propellants are presented. Initial observations are made comparing instantaneous results, corresponding time-averaged and steady-state solutions in the near -injector flow field. Significant differences in the flow fields exist, as expected, and are discussed. An important preliminary result is the identification of a fundamental mixing mechanism, accounted for by URANS and LES, but missing in the steady BANS methodology. Since propellant mixing is the core injector function, this mixing process may prove to have a profound effect on the ability to more correctly simulate injector performance and resulting thermal environments. Issues important to unifying the basis for future comparison such as solution initialization, required run time and grid resolution are addressed

Post-traumatic stress disorder, emotional processing and Inappropriate Implantable Cardioverter-Defibrillator Shocks: clinical consideration by a single case report = Disturbo post-traumatico da stress, profilo cognitivo-emotivo e shocks inappropriati del defibrillatore cardiaco impiantabile: Considerazioni cliniche attraverso un single case report

Introduction. Even though an overwhelming amount of evidence supports the clinical efficacy and safety of the implantable cardioverter defibrillator (ICD), inappropriate shocks for atrial arrhythmias with rapid ventricular conduction or for abnormal sensing results in multiple adverse effects Presentation. In this study we present the case of a 59- year-old woman who was admitted to hospital for ICD implantation with a past medical history that was positive for non-ischemic dilated cardiomyopathy, congestive heart failure (NYHA class III), atrial fibrillation, essential hypertension and a recent episode of syncope. Since in the 18 months follow-up the patient suffered many inappropriate shocks, we investigated the association of the presence of a PTSD (Post- Traumatic-Stress-Disorder) prior to implantation and a specific profile of cognitive processing emotions, with the effectiveness of the ICD. Emotional distress states and cognitive thoughts preceding ICD shock inappropriate episode were recorded by structured mobile diary (eMotional-ICDiary). We outlined how the presence of a highly traumatic event which had occurred 6 years previously was related to a recurrence of a combination of moderate distress and cognitive thoughts, associated with episodes of Inappropriate Shock. A psycho-diagnostic examination and the administration of the Emotional Processing Scale (EPS-25) and Emotional Regulation Questionnaire (ERQ) outlined that the patient presented a profile of cognitive processing of emotions characterized by elevated levels of unprocessed emotions, low appraisal and high suppression emotional regulation strategy. Conclusion. The observations gathered in this single case are a good starting point for further research in order to check if the post-traumatic stress disorder and a specific cognitive profile connected to the processing of emotions are associated with the presence of inappropriate ICD shocks. Further larger sample studies are required in this area

On the Existence and Stability of Limit Cycles for Transverse Acoustic Oscillations in a Cylindrical Combustion Chamber. 1: Standing Modes

Nonlinear pressure oscillations in combustion chambers have been studied using an approximate analysis which treats the unsteady motions as a collection of coupled nonlinear oscillators, each corresponding to an acoustic mode of the chamber. Based on spatial and temporal averaging of the conservation equations, the formulation provides a convenient means for analyzing the nonlinear behavior of acoustic wave motions. The work addresses the linear and nonlinear characteristics of transverse acoustic waves in a cylindrical chamber, with attention focused on the conditions for the existence and stability of limit cycles. As a result of the special structure of the equations, both general and precise conclusions can be reached. Explicit results are given for the special cases of two and three standing modes. Spinning wave motions will be treated in a subsequent paper