1,720,989 research outputs found
A two-step godunov-type scheme for the euler equations
No full textA second-order Godunov-type scheme for the Euler equations in conservation form is derived. The method is based on the ENO formulation proposed by Harten et al. The fundamental difference lies in the use of a two-step scheme to compute the time evolution. The scheme is TVD in the linear scalar case, and gives oscillation-free solutions when dealing with nonlinear hyperbolic systems. The admissible time step is twice that of classical Godunovtype schemes. This feature makes it computationally cheaper than one-step schemes, while requiring the same computer storage. © 1991 Kluwer Academic Publishers
Q1d modeling of hydrodynamic instabilities in solid rocket motors
No full textThis work concerns the investigation of a Q1D methodology employed to study pressure oscillations in solid rocket motors driven by hydrodynamic instabilities. A laboratory-scale solid motor designed to develop vortexshedding phenomena is analyzed for the whole firing time. The comparison between numerical results and experimental data shows good agreement regarding pressure oscillations signature, especially in the flute-mode behavior, the typical oscillations frequency trend present in any motor liable to hydrodynamic instabilities. Such result ensures the model capability to cope with this particular kind of pressure oscillations source, allowing the investigation of the phenomenon with a lighter and cost savings methodology than CFD simulations
Performance reconstruction of VEGA solid rocket motors: VERTA flights experience
No full textVega is the ESA launch vehicle designed to inject small satellites into Low Earth Orbit. It is a 3 m-diameter single-body vehicle, standing 30 m tall with a lift-off mass of 137metric tonnes. It has three solid-propellant stages and a liquid-propellant upper module for attitude and orbit control, and satellite release. Following Vega maiden flight on 13 February 2012, ESAs Verta (Vega Research and Technology Accompaniment) programme was set up with the main objective of providing a framework for the smooth transition of Vega launch system from development to exploitation. In this work, the analysis and performance reconstruction of the solid rocket motors of the Vega launch vehicle for the qualification flight and the five Verta flights is carried out with a post-firing 0D quasi-steady performance reconstruction model, developed for the purpose and already used in the past for the analysis of the static firing tests. The aim is to use the firing and flight measures available in order to evaluate the behavior of the motor, through the reconstruction of the non-ideal parameters: combustion efficiency, thrust efficiency, hump curve, scale factor and nozzle throat area evolution. The final goal is to increase the understanding of VEGA’s solid rocket motors behavior in terms of non-ideal parameters in order to assess the overall motor performance, to enrich the knowledge of the motor behavior, to characterize motor dispersion and scattering, and to consolidate the methodology used for the performance reconstruction
Q1D modelling of vortex-driven pressure oscillations in aft-finocyl SRMs with submerged nozzle cavity
No full textThis paper has the aim to investigate the aero-acoustic coupling that occurs typically in large aft-finocyl SRMs with submerged nozzle configurations, leading the onset of sustained pressure and thrust oscillations during the motor firing, by means of a Q1D model of the SRM aero-acoustic and vortex sound generation. The model has been applied successfully for the characterization of the pressure oscillations due to angle vortex shedding and the aero-acoustic coupling of P80 SRM, first stage of the VEGA launcher. The P80 pressure oscillations phases are characterized with a good correlation with the experimental data, identifying the different characteristics of the owfield conditions for the first two blows (that occur when the aft-region of the SRM burns), with respect to the other two blows (which occur when the aft-region of the SRM is completely burnt out). In particular, the effect of the submergence cavity within the Q1D vortex sound generation model is investigated by means of proposed closures for the characterization of the cavity behaviour and compared by means of a parametric analysis with a benchmark numerical solution and the experimental data of the firings. Results show that for the first two blows, occurring when the submergence cavity burns and is active in terms of mass addition, the role of the cavity model is almost negligible, or very small, and well correlated with the dispersion of the experimental data of the P80 pressure oscillations. Instead, for the third and fourth blows, that occur when the cavity is empty of propellant grain, the cavity model plays a role on the aeroacoustic coupling, showing that the the feedback loop between the angle vortex shedding and the chamber acoustics is in uenced by the cavity response
Multigrid acceleration of second-order eno schemes from low subsonic to high supersonic flows
No full textIn the present work the multigrid strategy is applied to second-order ENO schemes for the computation of steady compressible flows. The performances of the algorithm are analysed in many flow situations, ranging from low subsonic to high supersonic flows, for both internal and external problems. Three different Riemann solvers were considered in the study of computational efficiency and solution accuracy
Effective semi-empirical model of nozzle thermo-chemical erosion in solid rocket motors
No full textSolid rocket motors for launch vehicle, since their typical high operative pressure and long combustion time, are inherently subjected to nozzle throat erosion phenomena due to their intrinsic functioning. The nozzle ablation needs to be considered during the SRM design phase, in order to match the desired SRM performance, but also for the exploitation phase of the SRM, since it is important for the characterization of the SRM actual functioning (defined through non-ideal parameters and SRM actual efficiencies). The nozzle throat erosion entails performance loss, due to the reduction of the nozzle expansion ratio during time with respect to the initial one, which are the more relevant, the smaller is the SRM, for the same average operative pressure and combustion time. This paper presents an effective semi-empirical model of nozzle throat erosion of SRMs working in diffusionlimited regime (typical of modern aluminized propellant grains), which introduces the main dependency of the phenomenon: nozzle size and shape, propellant grain and nozzle thermal protections characteristics and motor operative conditions. The semi-empirical model is shown to be well correlated with full-CFD characterization of the nozzle throat erosion phenomena, for a wide range of SRMs and propellant grain, providing the assessment of the nozzle throat erosion in good agreement with the experimental data of the three solid stages of VEGA launch vehicle (P80, Zefiro 23 and Zefiro 9), for the static firing tests performed during VEGA development phas
Analysis & reconstruction of pressure oscillations during P80 steady-state of VEGA flights
No full textPressure oscillations can characterize the steady phase of large solid rocket motors, entailing dynamic loads on the launch vehicle structure and thrust oscillations. Both the modern large lower stage/booster configurations, segmented SRMs - e.g. Ariane 5 and Space Shuttle boosters - and monolithic finocyl SRMs - e.g. P80 of VEGA, are prone to pressure oscillations phenomena, at frequencies of the firsts longitudinal modes of the combustion chamber, with different characteristics time windows: during the second half of the SRM functioning, for the segmented SRMs; during the first half of the operative life, for the aft-finocyl configurations. This study is aimed at presenting the analysis of pressure oscillations of a real aft-finocyl SRM, addressing the following points: discuss and analyse the signature with the associated dispersion of the pressure oscillations phenomena (both in time and frequency domain) of the aft-finocyl first stage of the European launch vehicle VEGA, P80 SRM, exploiting the flight data from the first six flights over the nine successfully flown to date; provide a reconstruction and analysis of the pressure oscillation phenomena of the P80 SRM with the use of a Q1D aero-acoustic model of pressure oscillations in aft-finocyl SRMs, named AGAR, showing the capability of the model to represent with good correlation the whole experimental signature of the pressure oscillations experienced by P80 SRM during the flights
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