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

Liquid column separation due to fluid hammer occurrence in propellant lines

This version of the article has been accepted for publication, after peer review, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.2514/1.B38451[Abstract]: When a pressurized liquid enters a pipeline with a closed-end and under vacuum conditions, the resulting liquid front suddenly is brought to rest at the end of the pipe. This type of flow configuration is found in propulsion systems of satellites during priming operation and induces a fluid hammer followed by a column separation, generating a multiphase gas/vapor bubble. This paper aims at explaining the column separation mechanism by solving the momentum equation for the liquid column moving in the pipeline when column separation occurs, and by applying the integral form of the conservation principles to expansion and compression waves within the flow. The resulting model provides the velocity and position of the liquid front during column separation. Thus, the size and duration of the multiphase bubble can be determined, and the variables involved in the process are identified, which helps on the analysis of applications where this complex phenomenon is involved. It is shown that the initial velocity of the liquid front during column separation is the main parameter, which itself is a function of the fuel tank pressure and the fluid hammer pressure rise. The comparison of the predictions with experimental data shows an excellent agreement.This research was supported by the Xunta de Galicia and the European Regional Development Funds under grant EDC431C-2021/39 and the Spanish Science and Education Ministry through grant RTI2018-101114-B-I00. We wish to acknowledge the support received from the Centro de Investigación de Galicia, funded by Xunta de Galicia and the European Regional Development Fund Galicia 2014–2020 Program through grant ED431G 2019/01. The present research activity was promoted by the European Space Research and Technology Centre of the European Space Agency through the General Support Technology Programme (GSTP) activity AO/1-6210/09/NL/CP.Xunta de Galicia; EDC431C-2021/39Xunta de Galicia; ED431G 2019/0

Effect of inertia on the dynamic contact angle in oscillating menisci

The contact angle between a gas-liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is not clear whether they hold in presence of inertia and in the case of perfect wetting fluids. We analyze the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, i.e. HFE7200 (perfect wetting) and demineralized water. The set-up consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, and we fit interface models to the experimental data to estimate the contributions of all the governing forces and the contact angle. Traditional interface models fail to predict the interface shape and its contact angle at large interface and contact line accelerations. We propose a new model to account for the acceleration, and we discuss its impact on the measurement of the transient contact angle

Design of a Flush Air Data Sensing System for the Hypersonic Flight Experiment HEXAFLY-INT

The HEXAFLY-INT flight vehicle is a small-scale flight demonstrator of a supersonic passenger aircraft [8,9]. In order to determine the flight angles, Mach number and altitude for this vehicle a set of pressure sensors can be used to derive this data. In the frame of this study such a system, usually called Flush Air Data Sensing system (FADS), was designed and adapted to the constrains imposed by the vehicle shape of HEXAFLY-INT. Different theoretical, analytic and numerical approaches from local inclination method to numerical simulations were used to optimize sensor positions for the flight path of HEXAFLY-INT. Afterwards these different approaches was assessed and benchmarked against each other. In the second part of this work different algorithms are investigated to determine the flight properties for simulated inputs and were analyzed in terms of accuracy and real-time performance

Analysis of fluid hammer occurrence with phase change and column separation due to fast valve opening by means of flow visualization

This is a PDF file of an unedited manuscript that has been accepted for publication[Abstrac]: This paper presents an experimental investigation on the fluid hammer phenomenon generated when filling a pipe line under vacuum conditions with a closed end. This physical configuration, although it can be found in many piping configurations, it is of special interest in propulsion systems of satellites during priming operation. The fluid hammer taking place here not only leads to high pressure peaks in the fluid but also to low pressures, which can cause cavitation, gas desorption and liquid column separation. The study is carried out on a facility allowing flow visualization, which is achieved by replacing the pipe closed end by a quartz cylinder drilled with the same tube inner diameter. In this way, the flow can be recorded with high speed imaging at this location. The visualizations confirm that the pressure evolution is accompanied by a complex multiphase flow pattern. First of all, a foamy mixture of non-condensable gas, vapor and liquid droplets precedes the liquid front arrival at the bottom end. During the fluid hammer compression wave, the vapor condensates and the non-condensable gas gets compressed. Afterwards, the arrival of an expansion wave induces the movement of the liquid column backwards, with the corresponding pressure drop that generates a gaseous bubble referred to as column separation. Finally, the collapse of this bubble is at the origin of the next pressure rise.The present research activity was initiated and promoted by the European 280 Space Research and Technology Centre of the European Space Agency (ESTEC/ESA) through the GSTP activity AO/1-6210/09/NL/C

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

Upgrade of HyCost methodology and tool to support LCC estimation of reusable access to space vehicles

This paper aims at presenting the latest upgrades to HyCost Methodology and Tool, developed by Politecnico di Torino under funding and supervision of the European Space Agency (ESA), to support Life Cycle Cost (LCC) estimation of reusable access to space vehicles. The main idea is to support the designer in cost estimation activity during conceptual and preliminary design phases, allowing the evaluation of Research, Development, Test and Evaluation (RDTE) Costs, Production Costs, as well as Direct and Indirect Operating Costs (DOC and IOC), for a wide set of aerospace systems, from supersonic civil aircraft to hypersonic and, in general, high speed vehicles. Politecnico di Torino has already proposed a LCC methodology and tool called “HyCost 1.0” specifically tailored to air-breathing high-speed transportation systems. This paper discloses the upgrades of HyCost 1.0, i.e. “HyCost 2.0” methodology, to extend the methodology and tool capability to future Reusable Access to Space Vehicles. The main goal of this research activity is to evaluate the applicability of already existing parametric cost estimation relationships (CERs) to the peculiarities of Reusable Access to Space Vehicles and if necessary, to define new equations. Specifically, this new set of equations shall be able to capture the impact of different vehicle configurations (e.g. staging strategy, staging Mach number, parallel or series configuration, etc…) onto costs, as well as the impact of the most promising propulsive solutions, ranging from scramjet and combined cycle engines to rocket engines. Ultimately, this new methodology and implemented routines are applied and validated using the SpaceX Starship case study

HEXAFLY-INT: An Overview of Waverider Subsonic Investigations

Hypersonic waveriders have the potential to significantly reduce travel times on long haul civilian transport routes. The design of hypersonic aircraft is heavily influenced by the aerodynamic efficiency at the cruise Mach number, resulting in less than ideal geometries for subsonic flight. Waverider aerodynamics and stability in the low speed regime is rarely investigated and not well understood, but is crucial for horizontal take-offs and landings. This paper gives an overview of all work completed within the HEXAFLY-INT project with respect to subsonic investigations. It covers a wide range of static and dynamic wind tunnel tests in the longitudinal and lateral-directional planes. The experimental investigations are complemented by in depth numerical computations which validate the experimental data. It was found that flow separation, non-linear vortex lift and subsequent bursting at high angles of attack govern the aircraft stability derivaties. This is due to the low aspect ratio, highly swept delta wings which are present on the vehicle, as well as sharp edges which give rise to high pressure gradients at moderate angles of attack

Life cycle cost estimation methodology for hypersonic transportation systems

In this last decade, both the aeronautical and aerospace domains are looking with special interest towards the development of hypersonic transportation systems with different purposes. Indeed, considering the specific technologies that have been installed on-board, the vehicle can allow performing recurrent access to space (with reusable vehicles), suborbital parabolic flights with commercial or scientific purposes or point-to-point connections. In order to enhance the competitiveness of the project, cost analyses should be carried out since the very beginning of the design process taking into account not only Research & Development Costs and Production Costs, but also the Operating Costs. The lack of cost models for the segment of reusable high-speed vehicles is a problem in estimating the total effort from design, production up to exploitation. The formalization of a dedicated model for the estimation of development, production and operative costs of reusable transportation vehicles is therefore a crucial need. In this context, the proposed work deals with the generation of a parametric cost estimation tool, which consists of several Cost Estimation Relationships (CERs) for the overall reusability development, production and operating costs. The derived model is exploited to perform a preliminary cost assessment for the main vehicles designed within the LAPCAT (Long-Term Advanced Propulsion Concepts and Technologies) projects

Phase Change Material Heat Accumulator for the HEXAFLY-INT Hypersonic glider

International audienceFrom the launchers to the spacecrafts, various on-board systems have to be maintained within specified temperature limits. Phase Change Materials (PCM) offer the possibility to store thermal energy directly as latent heat of fusion. Among the advantages of a PCM device are the stability of temperature control, the absence of moving parts and a reduced mass. The HEXAFLY-INTERNATIONAL project aims to flight test an experimental vehicle above Mach 7 to verify its potential for a high aerodynamic efficiency during a free-flight. European Major Resarch Centers and Industries are collaborating on this challenge. The presented activity focus on the use of a Phase Change Material device already developed under ESA projects up to TRL 6. Two efficient heat accumulators using PCM will allow avoiding overheating of electronic units such as telemetry & telecommand receivers, transmitters and data acquisition units for the hypersonic flight. The paper presents the complete cycle of design and environmental testing for the two PCM Heat Accumulators selected for the flight. The conclusions will show the benefit of adopting a Phase Change Material Heat Accumulator