Multigrid methods for compressible Navier-Stokes equations in low-speed flows

AbstractThe multigrid performance of pointwise, linewise and blockwise Gauss-Seidel relaxations for compressible laminar and turbulent Navier-Stokes equations is illustrated on two low-speed test problems: a flat plate and a backward facing step. The line method is an Alternating Symmetric Line Gauss-Seidel relaxation. In the block methods, the grid is subdivided into geometric blocks of n × n points with one point overlap. With in the blocks, the solution is obtained by a direct method or with an alternating modified incomplete lower-upper decomposition. The analysis is focused on flows typical for boundary layers, stagnation and recirculation regions. These are characterized by very small Mach numbers, high Reynolds numbers and high mesh aspect ratios

Design optimization of multi-functional multi-lobe cryogenic fuel tank structures for hypersonic vehicles

[Abstract:] Hypersonic hydrogen-powered cruise vehicles offer promise for economical and reliable high-speed atmospheric transport. In recent years, several vehicle concepts have been developed in which the integration of fuel tanks is a major challenge, as they feature complex aerodynamic designs. In this work, we explore the viability of multi-lobe hydrogen tanks as a solution to obtain lightweight and volume-efficient structures. To do so, a parametric finite-element model was developed to fit multi-lobe geometries inside hypersonic vehicles. The parametric model was then incorporated into an optimization that minimizes the mass and maximizes the fuel capacity of the tank. The methodology is organized in two steps: the global search is driven by a two-level optimization consisting of a genetic algorithm with a nested gradient-based method; and a local search where each design is further improved to obtain a Pareto front. As presented in the results, this is a promising approach for designing multi-lobe tanks for complex geometries.The research leading to these results has been conducted under Grant PID2019-108307RB-I00 funded by MCIN/AEI/10.13039/501100011033. The authors also acknowledge funding received from the Galician Government through research grant ED431C 2021/33. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.Xunta de Galicia; ED431C 2021/3

Life-Cycle Cost Estimation for High-Speed Vehicles: from the engineers’ to the airline’s perspective

This paper aims at upgrading the holistic Cost Estimation methodology for High-Speed Vehicles already developed by Politecnico di Torino and the European Space Agency (ESA) to encompass different stakeholders’ perspectives. In details, the presented methodology combines International Air Transport Association (IATA) best practices with a detailed Life- Cycle Cost (LCC) assessment, which includes the evaluation of Research, Development, Test and Evaluation (RDTE) Costs, Production costs and of Direct and Indirect Operating Costs (DOC and IOC). The integrated approach allows to further extend the capabilities of the inhouse developed HyCost tool to support all the actors of the product value-chain (including engineers, manufacturers, airlines and customers) in assessing the economic sustainability of a newly under-development high-speed vehicle. However, considering the need of providing all these cost analyses perspectives since the early design stages, the derived Cost Estimation Relationships are mainly derived on statistical bases. To cope with the uncertainties that affect the initial statistical population and consequently, the CERs, this paper presents each cost item together with the estimation of related prediction intervals. Finally, results of the application of the upgraded cost estimation methodology and of the upgraded tool to the LAPCAT MR2.4 high-speed civil transport are reported and discussed

A methodology for preliminary sizing of a Thermal and Energy Management System for a hypersonic vehicle

This paper addresses a methodology to parametrically size thermal control subsystems for high-speed transportation systems during the conceptual design phase. This methodology should be sufficiently general to be exploited for the derivation of Estimation Relationships (ERs) for geometrically sizing characteristics as well as mass, volume and power budgets both for active (turbopumps, turbines and compressors) and passive components (heat exchangers, tanks and pipes). Following this approach, ad-hoc semi-empirical models relating the geometrical sizing, mass, volume and power features of each component to the operating conditions have been derived. As a specific case, a semi-empirical parametric model for turbopumps sizing is derived. In addition, the Thermal and Energy Management Subsystem (TEMS) for the LAPCAT MR2 vehicle is used as an example of a highly integrated multifunctional subsystem. The TEMS is based on the exploitation of liquid hydrogen boil-off in the cryogenic tanks generated by the heat load penetrating the aeroshell throughout the point-to-point hypersonic mission. Eventually, specific comments about the results will be provided together with suggestions for future improvements

Heat flux augmentation caused by surface imperfections in turbulent boundary layers

Aerodynamic heating of hypersonic vehicles is one of the key challenges needed to be overcome in the pursuit of hypersonic ascent, re-entry, or sustained flight. Small, unavoidable imperfections are always present on the surface of aircraft in the form of steps, gaps, and protuberances. These can lead to high levels of localised heat flux augmentation, up to many times the undisturbed level. Flat plate experiments have been carried out in the Oxford High Density Tunnel with the aim of characterising the heating effects caused by small scale protuberances and steps in turbulent boundary layers. The current work presents experimental heat flux augmentation data, an assessment of existing heat flux correlations, and introduces new engineering level correlations to describe heat flux augmentation for a range of surface geometries

A methodology for preliminary sizing of a Thermal and Energy Management System for a hypersonic vehicle

This paper addresses a methodology to parametrically size thermal control subsystems for high-speed transportation systems. This methodology should be sufficiently general to be exploited for the derivation of Estimation Relationships (ERs) for geometrically sizing characteristics as well as mass, volume and power budgets both for active (turbopumps, turbines and compressors) and passive components (heat exchangers, tanks and pipes). Following this approach, ad-hoc semi-empirical models relating the geometrical sizing, mass, volume and power features of each component to operating conditions have been derived. As a specific case, a semi-empirical parametric model for turbopumps sizing is derived. In addition, the Thermal and Energy Management Subsystem (TEMS) for the LAPCAT MR2 vehicle is used as an example of a highly integrated multifunctional subsystem. The TEMS is based on the exploitation of liquid hydrogen boil-off in the cryogenic tanks generated by the heat load penetrating the aeroshell, all along the point-to-point hypersonic mission. Eventually, specific comments about the results will be provided together with suggestions for future improvements

Fuel pyrolysis through porous media: Coke formation and coupled effect on permeability

International audienceThe development of hypersonic vehicles (up to Mach 10) leads to an important heating of the whole structure. The fuel is thus used as a coolant. It presents an endothermic decomposition with possible coke formation. Its additional permeation through the porous structure involves internal convection. This implies very complex phenomena (heat and mass transfers with chemistry). In this paper, the n-dodecane pyrolysis is studied through stainless steel porous medium up to 820 K and 35 bar (supercritical state). The longitudinal profiles of chemical compositions inside the porous medium are given thanks to a specific sampling technique with off-line Gas Chromatograph and Mass Spectrometer analysis. By comparison with previous experiments under plug flow reactor, the conversion of dodecane is higher for the present experimental configuration. The pyrolysis produces preferentially light gaseous species, which results in a higher gasification rate for a similar pyrolysis rate. The effects of the residence time and of the contact surface area are demonstrated. The transient changes of Darcy's permeability are related to the coke formation thanks to previous experimental relationship with methane production. A time shift is observed between coke chemistry and permeability change. This work is quite unique to the author's knowledge because of the complex chemistry of heavy hydrocarbon fuels pyrolysis, particularly in porous medium