Inviscid supersonic minimum length nozzle design

An aerospace vehicle is accelerated by a propulsion system to a given velocity. A nozzle is used to extract the maximum thrust from high pressure exhaust gases generated by the propulsion system. The nozzle is responsible for providing the thrust necessary to successfully accomplish the mission while its design efficiency translates to greater payload and reduction in propellant consumption. Specifically, the nozzle is that portion of the engine beyond the combustion chamber. Typically, the combustion chamber is a constant area duct into which propellants are injected, mixed and burned. Its length is sufficient to complete the combustion of the propellant before the nozzle accelerates the gas products. The nozzle is said to begin at the point where the chamber diameter begins to decrease. This paper exploits the De Laval nozzle, a convergent divergent nozzle invented by Carl De Laval toward the end of the 19th century, and it tries to give a practical procedure to design the nozzle of minimum length. The basic assumption made is that the boundary layer thickness is small compared to the characteristic length, i.e. nozzle radius, so that the nozzle flow field can be treated as inviscid for the purpose of designing the aerodynamic lines. Ones the aerodynamic lines are determined, a correction can be made to account for the displacement thickness of the boundary layer. This second step of the designing procedure is not treated in here. This basic procedure has been applied successfully to many supersonic nozzle

The CFD code karalis

Karalis is a paralle MPI, Finite-Volume, multiblock CFD code which solves the fully compressible Euler and Navier-Stokes equations where all couplings between dynamics and thermodynamics are allowed. This the most general mathematical model for all fluid flows. The code solves the coupled system of continuity, momentum and full energy equation for the velocity components, pressure and temperature. Once, u, v, w, p are and T are updated, arbitrary thermodynamics is supplied. The second order Roe’s upwind TVD scheme is used to compute convective fluxes through the Finite-Volume cell interfaces. A V-cycle Coarse Grid Correction Multi-Grid algorithm is used, together with a 5-stage Runge-Kutta explicit time-marching method, to accelerate convergence to a steady state. This formulation, typical of aerodynamic flows, shows an eccellent efficiency even for incompressible flows as well as for flows of incompressible fluids (typically buoyancy flows), once equipped with a preconditioner. Merkel’s preconditioner has been chosen because it can be easily formulated for arbitrary equations of state given as a functional relation of two independent thermodynamic variables (typically the pressure p and the temperature T), or even in tabular form, read in as an input file and used with bilinear interpolation. Karalis implement two among the most popular turbulence models, namely the one-equation model by Spalart and Allmaras and the two-equations model by Wilcox, the k-ω model, which allow a good compromise between accuracy, robustness and stability of turbulent calculations. Code validation is presented for some typical benchmark test cases of incompressible fluid dynamics. Comparison with solutions obtained with a few popular commercial CFD codes is also presented

Physiological responses and energy cost of walking on the Gait Trainer with and without body weight support in subacute stroke patients

BACKGROUND: Robotic-assisted walking after stroke provides intensive task-oriented training. But, despite the growing diffusion of robotic devices little information is available about cardiorespiratory and metabolic responses during electromechanically-assisted repetitive walking exercise. Aim of the study was to determine whether use of an end-effector gait training (GT) machine with body weight support (BWS) would affect physiological responses and energy cost of walking (ECW) in subacute post-stroke hemiplegic patients. METHODS: Participants: six patients (patient group: PG) with hemiplegia due to stroke (age: 66 ± 15y; time since stroke: 8 ± 3 weeks; four men) and 6 healthy subjects as control group (CG: age, 76 ± 7y; six men). Interventions: overground walking test (OWT) and GT-assisted walking with 0%, 30% and 50% BWS (GT-BWS0%, 30% and 50%). Main Outcome Measures: heart rate (HR), pulmonary ventilation, oxygen consumption, respiratory exchange ratio (RER) and ECW. RESULTS: Intervention conditions significantly affected parameter values in steady state (HR: p = 0.005, V’E: p = 0.001, V'O(2): p < 0.001) and the interaction condition per group affected ECW (p = 0.002). For PG, the most energy (V’O(2) and ECW) demanding conditions were OWT and GT-BWS0%. On the contrary, for CG the least demanding condition was OWT. On the GT, increasing BWS produced a decrease in energy and cardiac demand in both groups. CONCLUSIONS: In PG, GT-BWS walking resulted in less cardiometabolic demand than overground walking. This suggests that GT-BWS walking training might be safer than overground walking training in subacute stroke patients

sasurfer/StatisticalAnalysis4CDRsSurvey: updated 2d projections plot

Statistical Analysis Scripts used in CDRs survey analysi

sasurfer/FAMD-analysis: updated 2d projections plot

FAMD analysis of openEHR CDRs variable

sasurfer/StatisticalAnalysis4CDRsSurvey: Public tools

Statistical Analysis Scripts used in CDRs survey analysi

Development, implementation and numerical tests of implicit methods

The goal of this work was to implement an implicit version of Karalis, a Navier-Stokes equations solver. Besides the Spalart & Allmaras equation is formulated in an implicit way. In this paper the first part is devoted to the implementation details of the implicit Navier-Stokes equations while the latter to the Spalart & Allmaras equation. The routines are then briefly described

Vento di Sardegna. Messa a punto del codice di calcolo cfd rans (appendici)

Il lavoro presenta le Appendici del report VdS1.3B1 (Vento di Sardegna. Sviluppo della tecnica immersed boundaries), in particolar modo vengono analizzati i seguenti argomenti: vento apparente e strato limite atmosferico; forze e momenti generati dal carico aerodinamico; il codice di calcolo

Vento di Sardegna. Sviluppo della tecnica immersed boundaries

In questo report l’attenzione sarà posta sullo sviluppo e l’implementazione di un cut cells method che sia applicabile al particolare problema della simulazione del flusso intorno alle vele. Il capitolo 2 é un capitolo introduttivo al solutore in-house che é stato utilizzato come base per l’implementazione dei metodi in 2d. Nel capitolo 3 sarà presentato un primo metodo, molto semplice da implementare, in particolare per la parte riguardante il solutore, e ne saranno descritte le varianti nel tentativo di migliorarne i risultati. Nei successivi due capitoli saranno presentati in dettaglio i metodi proposti da Forrer e da Dadone, e ne saranno discusse le problematiche d’implementazione. Ogni capitolo è ulteriormente suddiviso in tre parti: la prima parte è dedicata al preprocessore ovvero al calcolo di tutte quelle quantità relative alla griglia ed alla geometria che sono necessarie al solutore e che sono indipendenti dalla soluzione; la seconda parte é incentrata sul solutore e sulle routine che é stato necessario aggiungere o modificare rispetto al solutore iniziale trattato nel capitolo 2; la terza parte riguarda i risultati e l’analisi critica degli stessi

Vento di Sardegna. Messa a punto del codice di calcolo cfd rans

Il presente documento illustra i risultati ottenuti nell’ambito dell’attività 1.3 dell’Obiettivo Realizzativo 1 del progetto Vento di Sardegna: “messa a punto e integrazione dei diversi software per la simulazione”. In particolare viene presentato il lavoro svolto per la realizzazione dell’attività di messa a punto del codice di calcolo CFD RANS. L’attività di analisi fluidodinamica fatta mediante l’uso del calcolo nell’ambito del progetto di ricerca costituisce di fatto una sorta di galleria del vento virtuale. Allo stesso modo di ogni altro strumento di analisi, anche il codice di simulazione necessita di una fase di “taratura”. In altre parole, per lo specifico problema e per le specifiche condizioni di flusso, si deve cercare di ottimizzare l’insieme dei parametri della simulazione (estensione del dominio di calcolo, condizioni al contorno, dimensione della griglia, modellistica fisica utilizzata), al fine di avere uno strumento in grado non solo di riprodurre le evidenze sperimentali in condizioni note, ma anche di fornire utili indicazioni per lo sviluppo di nuove soluzioni progettuali