1,721,208 research outputs found
Associate Fellow AIAA
No full textAIAA Associate Fellows are individuals of distinction who have made notable and valuable contributions to the arts, sciences, or technology of aeronautics or astronautics
Numerical Analysis of LNG as a Coolant in Liquid Rocket Engines
No full textLiquid Natural Gas (LNG) is a suitable propellant to be used, together with liquid oxygen as oxidizer, in a liquid rocket engine, because of possible advantages with respect to hydrogen in specific applications. Often approximated as pure methane, LNG is a mixture of methane, other heavier hydrocarbons and nitrogen. If LNG is to be used in a regeneratively cooled liquid rocket engine the knowledge of the thermodynamic and heat transfer characteristics when it flows in the cooling channels is of primary importance. This is especially true in the case of expander cycle engines for which the performance is strictly connected with the coolant heat transfer characteristics. The aim of the present work is to understand how the composition of LNG can influence the flow in the cooling channels. A parametric study is carried out considering different LNG compositions. Attention is devoted to the pressure drop and the heat transfer behavior, which are the aspects that have to be controlled in a regenerative cooling system
Carbon-carbon nozzle erosion and shape change in full-scale solid-rocket motors
No full textThe erosion of nozzle protection materials during solid-rocket-motor burning needs to be accounted for to get reliable performance predictions, especially for long-duration firings.Astudy is conducted to predict carbon–carbon nozzle erosion behavior in full-scale solid-rocket motors for wide variations of motor operating conditions. The numerical model considers the solution of Reynolds-averaged Navier–Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, ablation species injection in the boundary layer, variable multicomponent transport and thermodynamic properties, and heat conduction in the nozzle material. Two different ablation models are considered: a diffusion-limited approach and a finite-rate approach. The numerical model is used to study the erosion of carbon–carbon nozzle inserts for the second- and third-stage solid-rocket motors of the European Vega launcher. The effect of variable chamber pressure over the burning time and the effect of nozzle shape change on the erosion rate are taken into account in the numerical analysis. The obtained results show a very good agreement with the measured final eroded profile along the entire carbon–carbon nozzle throat insert for both motors. The shape-change effect is shown to be an important factor that has to be taken into account to get a good prediction of the throat erosion for long-duration firings
Numerical Aspects of the Solution of the Non-Conservative Navier-Stokes Equations for High Speed Flows
No full textThe numerical solution of the laminar Navier-Stokes equations for high-speed flows is considered. The equations are written in non-conservative form, and the shocks treated by a shock-fitting technique which allows accurate predictions of the shock location and of its propagation velocity. Since a critical point of the numerical calculations of viscous high speed flows is the prediction of the interaction between shock wave and boundary layer, numerical tests are performed to assess the capability of the present technique to handle these phenomena in both weak and strong interaction regimes
Best Paper Certificate of Merit for the purpose of promoting technical and scientific excellence in Solid Rockets
No full textThe erosion of rocket-nozzle materials during motor firing is one of the major limits in the advancement of solid-rocket propulsion. A study is conducted to predict carbon-carbon nozzle erosion behavior in solid rocket motors for wide variations of motor operating conditions. The numerical model considers the solution of Reynolds averaged Navier-Stokes equations in the nozzle, heterogeneous chemical reactions at the nozzle surface, variable multi-component transport and thermodynamic properties, and heat conduction in the nozzle material. Two different ablation models are considered: a surface equilibrium approach and a finite-rate approach. The numerical model is used to study the carbon-carbon nozzle throat insert erosion of the European VEGA launcher third stage and second stage solid rocket motors. The effect of variable chamber pressure over the burning time and the effect of nozzle shape change on the erosion rate are taken into account in the numerical analysis. The obtained results show a very good agreement with the measured final eroded profile along the entire carbon-carbon nozzle throat insert for both motors
Analysis of Unsteady Supersonic Viscous Flows by a Shock Fitting Technique
No full textAn extension of Moretti's classical shock-fitting technique is proposed to solve complicated unsteady viscous flows. This version allows the automatic treatment of flow structures featuring triple points and shock interactions. A fitting of contact discontinuities has also been introduced for a number of problems. The fitting procedure is used with a Navier-Stokes solver based on the A scheme. Validation tests for selected cases are presented
Theoretical Considerations on Shock Reflections and Their Implications on the Evaluations of Air Intake Performance
No full textMany theoretical studies have shown the existence of a hysteresis effect in the solution of oblique shock reflections. In fact, a wide domain of free-stream Mach number and shock angle values exists where regular reflection and Mach reflection are both possible solutions for the same flow conditions. Part of this domain overlaps the typical operating conditions of supersonic air intakes, and therefore it is of practical interest to obtain a deeper understanding of the theoretical problem. Indeed, although both solutions are theoretically possible, they yield very different flowfields and consequently large discrepancies in the evaluation of the air intake performance. Numerical solutions for steady configurations have been carried out and compared with the flow evolution obtained for time-dependent cases. The results have confirmed numerically the existence of the multiple solution domain where hysteresis takes place in time-dependent simulations. The analysis of the physical and numerical problems encountered has provided indications for a correct simulation in practical applications
An approximate Riemann solver for real gas parabolized Navier-Stokes equations
No full textUnder specific assumptions, parabolized Navier-Stokes equations are a suitable mean to study channel flows. A special case is that of high pressure flow of real gases in cooling channels where large crosswise gradients of thermophysical properties occur. To solve the parabolized Navier-Stokes equations by a space marching approach, the hyperbolicity of the system of governing equations is obtained, even for very low Mach number flow, by recasting equations such that the streamwise pressure gradient is considered as a source term. For this system of equations an approximate Roe's Riemann solver is developed as the core of a Godunov type finite volume algorithm. The properties of the approximated Riemann solver, which is a modification of Roe's Riemann solver for the parabolized Navier-Stokes equations, are presented and discussed with emphasis given to its original features introduced to handle fluids governed by a generic real gas EoS. Sample solutions are obtained for low Mach number high compressible flows of transcritical methane, heated in straight long channels, to prove the solver ability to describe flows dominated by complex thermodynamic phenomena. (C) 2012 Elsevier Inc. All rights reserved
Methodology to solve flowfields of plug nozzles for future launchers
No full textIn the development of future launchers, in particular the single stage to orbit launcher, the use of plug nozzles looks promising because of the possibility of improving performance; therefore the capability to achieve accurate evaluations of the relevant flowfields is required. Nevertheless, because of typical flow features, analyses performed by the common computational fluid dynamics methods lead to uncertain and time-consuming results, To circumvent some of these problems an approach based on a simple simulation model that replaces the mixing layer between the nozzle jet and external flow by a contact discontinuity was recently proposed by the authors. Following this approach the complex calculation of the turbulent mixing of flows having different thermodynamic characteristics can be avoided, while correctly accounting for the main features of the flowfield. In this paper this simple model was implemented to compute linear plug nozzle flowfields at different ambient conditions and for different geometries of the plug. The expected flow behavior has been well reproduced and good agreement with the theoretical nozzle performance has been achieved, allowing a performance analysis for some of the main characteristic parameters to be carried out
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