1,720,994 research outputs found
Unstructured Shock-Fitting Calculations of the Transonic Flow in a Gas Turbine Cascade
No full textEven though shock-capturing techniques are the de-facto standard in the CFD simulation of turbo-machinery flows, the accurate estimation of shock-induced losses in transonic flows can be severely hindered by the numerical errors that are generated along a captured shock and convected downstream. Indeed, and despite their widespread use, shock-capturing techniques are known to be plagued by a number of drawbacks that are inherent to the numerical details of the shock-capturing process.
In recent works, the authors have developed a novel shock fitting technique for unstructured grids that has been applied to the computation of transonic, supersonic and hypersonic flows in both two and three space dimensions. In this paper, the proposed technique is applied to two-dimensional, transonic flows around an isolated profile and in a gas turbine cascade.
It is shown that the use of unstructured meshes allows to relieve most of the algorithmic difficulties that have contributed to the dismissal of the shock-fitting technique in the framework of structured meshes. Moreover, it is confirmed that, in contrast to shock-capturing, shock-fitting allows to obtain very accurate solution on coarse meshes
AERO-THERMAL ANALYSIS OF A REUSABLE LAUNCH VEHICLE DURING RE-ENTRY MANOEUVRER
No full textThe growing demand for space access, propelled by the continuous expansion of the space economy, stands as a primary motivator for the regain of interest for rockets re-usability. This paper aims at presenting the aero-thermal analysis of a simplified single-stage launch vehicle during both its ascent and descent path. In detail, 2D axissymmetric computations were performed using the commercial gas-dynamic code CFD++ to predict the aerodynamic heating on the launch vehicle wall. Thermal loads were evaluated using a Conjugate Heat Transfer (CHT) technique, implemented in the CFD++ solver, which couples the fluid-dynamic field around the launch vehicle with the solid one within the launch vehicle walls. Furthermore, some considerations regarding surface heating due to the retropropulsion maneuver are drawn in this wor
Extrapolated shock fitting for two-dimensional flows on structured grids
Full text linkOver the years the development of structured-grid shock-fitting techniques faced two main problems: the handling of a moving discontinuity on a fixed background grid and the capability of simulating complex flow configurations. In the proposed work, the authors present a new shock-fitting technique for structured-grid solvers that is capable of overcoming the limitations that affected the different approaches originally developed. The technique presented here removes the tight link between grid topology and shock topology, which characterizes previous shock fitting as well as front tracking methods. This significantly simplifies their implementation and more importantly reduces the computational overhead related to these geometrical manipulations. Interacting discontinuities and shocks interacting with a solid boundary are discussed and analyzed. Finally, a quantitative investigation of the error reduction obtained with the approach proposed via a global grid convergence analysis is presented
Effects of protuberances on surface loads on the vega-c launch vehicle
No full textThe need to meet the demands of the aerospace market in terms of payload capability, mission flexibility, and cost reduction has led the European Space Agency to develop Vega-C as an evolution of the original Vega launcher. The design of a modern launch vehicle like the Vega-C requires accurate evaluation of the thermal and mechanical loads on its surface under conditions as close as possible to real flight conditions. Despite its apparently simple aeroshape, the Vega-C surface is characterized by the presence of antennas, wiring ducts, flanges, and retrorockets. These protuberances interact with the external supersonic stream during the launcher's flight, giving rise to locally complex flows that can impose stresses on the launcher structure through the generation of severe mechanical and thermal loads. The present work focuses on an in-depth aerothermal analysis of Vega-C protuberances under specific flight conditions. Numerical computations are carried out using the commercial solver CFD++ on multiblock structured Chimera grids to assess which protuberances are subject to the most severe surface loads. Particular emphasis is placed on the role of boundary-layer thickness in the heat flux and pressure peaks that occur on the protuberances
Extrapolated discontinuity tracking for complex 2D shock interactions
Full text linkA new shock-tracking technique that avoids re-meshing the computational grid around the moving shock-front was recently proposed by the authors (Ciallella et al., 2020). The method combines the unstructured shock-fitting (Paciorri and Bonfiglioli, 2009) approach, developed in the last decade by some of the authors, with ideas coming from embedded boundary methods. In particular, second-order extrapolations based on Taylor series expansions are employed to transfer the solution and retain high order of accuracy. This paper describes the basic idea behind the new method and further algorithmic improvements which make the extrapolated Discontinuity Tracking Technique (eDIT) capable of dealing with complex shock-topologies featuring shock–shock and shock–wall interactions occurring in steady problems. This method paves the way to a new class of shock-tracking techniques truly independent on the mesh structure and flow solver. Various test-cases are included to prove the potential of the method, demonstrate the key features of the methodology, and thoroughly evaluate several technical aspects related to the extrapolation from/onto the shock, and their impact on accuracy, and conservation
An embedded shock-fitting technique on unstructured dynamic grids
Full text linkIn this paper, a new shock-fitting technique based on unstructured dynamic grids is proposed to improve the performances of the unstructured “boundary” shock-fitting technique developed by Liu and co-workers in [1, 2]. The main feature of this new technique, which we call the “embedded” shock-fitting technique, is its capability to insert or remove shocks or parts thereof during the calculation. This capability is enabled by defining subsets of grid-points (mutually connected by lines) which behave as either “common”- or “shock”-points, shock-waves being made of an ordered collection of shock-points. Two different sets of flow variables, corresponding to the upstream and downstream sides of the shocks, are assigned to the shock-points, which may be switched to common- and back to shock-points, a feature that allows to vary the length of the existing shocks and/or make new shock-branches appear. This paper illustrates the algorithmic features of this new technique and presents the results obtained when simulating both steady and un-steady, two-dimensional flows
A shock-fitting technique for 2D/3D flows with interactions using structured grids
No full textA novel shock-fitting algorithm is proposed in this paper. This technique has been designed to overcome the limitations that affected the originally developed shock-fitting approaches based on structured meshes: the handling of a moving discontinuity on a fixed background grid and the capability of simulating complex flow configurations. The present algorithm has been applied to high speed flows past three-dimensional bodies, such as a circular cylinder and a compression corner, providing high quality results with respect to the most common shock-capturing approaches
Extrapolated Shock Tracking: Bridging shock-fitting and embedded boundary methods
No full textWe propose a novel approach to approximate numerically shock waves. The method combines the unstructured shock-fitting approach developed in the last decade by some of the authors, with ideas coming from embedded boundary techniques. The numerical method obtained allows avoiding the re-meshing phase required by the unstructured fitting method, while guaranteeing accuracy properties very close to those of the fitting approach. This new method has many similarities with front tracking approaches, and paves the way to shock-tracking techniques truly independent on the data and mesh structure used by the flow solver. The approach is tested on several problems showing accuracy properties very close to those of more expensive fitting methods, with a considerable gain in flexibility and generality
NUMERICAL STUDY ON THE FIRST-STAGE RE-ENTRY TRAJECTORY USING AN INFLATABLE BALLUTE
No full textThis article proposes the use of inflatable ballutes to decelerate the first stage of a launcher during its reentry phase and to allow its recovery. In recent years, reusable launch vehicles (RLVs) have been proposed to significantly reduce the costs of space missions. The most famous case is the Falcon-9 first stage reused dozens of times. In this case the deceleration is producted by the propulsion system of the stage that is turned on during the re-entry. To evaluate the use of inflatable ballutes as an alternative braking systems, CFD simulations were performed using the conjugate heat transfer (CHT) technique. This technique allows to evaluate the drag and the heating caused by the high speed and by the exhaust gases of the propuslion system. The results show that the use of the inflatable ballutes decelerates much more than the use of retropropulsion reducing the amount of the necessary propellant and can reduce the heating of the side wall of the reusable stage during the descent
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