Refueling of LH2 Aircraft—Assessment of Turnaround Procedures and Aircraft Design Implication

Green liquid hydrogen (LH2) could play an essential role as a zero-carbon aircraft fuel to reach long-term sustainable aviation. Excluding challenges such as electrolysis, transportation and use of renewable energy in setting up hydrogen (H2) fuel infrastructure, this paper investigates the interface between refueling systems and aircraft, and the impacts on fuel distribution at the airport. Furthermore, it provides an overview of key technology design decisions for LH2 refueling procedures and their effects on the turnaround times as well as on aircraft design. Based on a comparison to Jet A-1 refueling, new LH2 refueling procedures are described and evaluated. Process steps under consideration are connecting/disconnecting, purging, chill-down, and refueling. The actual refueling flow of LH2 is limited to a simplified Reynolds term of v · d = 2.35m2/s. A mass flow rate of 20 kg/s is reached with an inner hose diameter of 152.4mm. The previous and subsequent processes (without refueling) require 9 min with purging and 6 min without purging. For the assessment of impacts on LH2 aircraft operation, process changes on the level of ground support equipment are compared to current procedures with Jet A-1. The technical challenges at the airport for refueling trucks as well as pipeline systems and dispensers are presented. In addition to the technological solutions, explosion protection as applicable safety regulations are analyzed, and the overall refueling process is validated. The thermodynamic properties of LH2 as a real, compressible fluid are considered to derive implications for airport-side infrastructure. The advantages and disadvantages of a subcooled liquid are evaluated, and cost impacts are elaborated. Behind the airport storage tank, LH2 must be cooled to at least 19K to prevent two-phase phenomena and a mass flow reduction during distribution. Implications on LH2 aircraft design are investigated by understanding the thermodynamic properties, including calculation methods for the aircraft tank volume, and problems such as cavitation and two-phase flows. In conclusion, the work presented shows that LH2 refueling procedure is feasible, compliant with the applicable explosion protection standards and hence does not impact the turnaround procedure. A turnaround time comparison shows that refueling with LH2 in most cases takes less time than with Jet A-1. The turnaround at the airport can be performed by a fuel truck or a pipeline dispenser system without generating direct losses, i.e., venting to the atmosphere. © 2022 by the authors.Licensee MDPI, Basel, Switzerland

Impact of the Number of Wing Stations on the Twist Distribution of a BWB Conceptual Aircraft Design in a MDAO Environment to Match Target Lift Distribution

The design of a blended wing body (BWB) has been the subject of numerous research projects worldwide, as it offers significant advantages over a conventional tube-and-wing configuration. The European Clean Sky 2 project NACOR investigated the potential of innovative unconventional aircraft architectures. A BWB configuration was identified to reducing fuel consumption by 10% compared to a relevant reference aircraft with entry into service 2035 and prevailed against box-wing or strut-braced wing aircraft. For this reason, the need to be capable of designing and evaluating BWB configurations was recognized. Especially for the design of BWBs, an optimized wing twist is important to achieve high aerodynamic performance, but on conceptual design level the number of wing stations is often limited to reduce complexity which impedes this optimization. Computationally expensive calculations such as Reynolds-averaged Navier-Stokes (RANS) or Euler method are required to optimize wing twist, but this reduces the number of possible designs examined in a given time. Therefore, this paper presents the feasibility of flexible number of wing stations to achieve an aerodynamically optimized wing twist for BWB architectures on conceptual aircraft design level with embedded low fidelity multi-lifting line approach. The aim of the flexible wing modelling combined with a multi-disciplinary design analysis and optimization (MDAO) aircraft design environment is to exploit the benefits of low computational costs and high flexibility with respect to the vehicle architecture to be analyzed with an adequate level of fidelity. The resulting fast analysis capability enables a wide range of possible sensitivity studies and optimizations to ensure a more robust aircraft design space exploration. The target lift distribution is determined by high fidelity RANS calculations and used as an objective function for the twist optimization. In addition, typical lift distributions, i.e. elliptical and triangular lift distributions, are used to benchmark the results. The final results show the influence of the number of wing stations on the resulting twist distribution, induced drag as well as the CPU cost, and provide a proposal for an appropriate number of wing stations to be used

Liquid hydrogen storage design trades for a short‑range aircraft concept

Preliminary design trades for the liquid hydrogen storage system of a short-range aircraft are presented. Two promising insulation methods, namely rigid foam and multilayer insulation, are identified as main design drivers. In addition, the maximal pressure and the shape of the hydrogen storage tank influence the aircraft performance and the insulation efficiency. In this study, the hydrogen storage tanks are integrated in wing pods. The main effects driven by the design parameters are addressed using conceptual and preliminary methods: models are carried out for the storage mass, additional drag, propeller efficiency loss and the dynamical thermodynamic behavior of the liquid hydrogen storage. These effects are coupled making an integrated design method necessary. For the sizing of the liquid hydrogen storage, a multidisciplinary workflow is set up including the aircraft sensitivities on the design mission block fuel. The trade-off study reveals the opposing trend between insulation efficiency and aircraft performance. For the insulation architecture based on rigid foam, the penalties implied by the storage tank on aircraft level and the penalties due to vented hydrogen can be balanced and result in minimal block fuel for the design mission. The application of multilayer insulation avoids venting during the design mission, but has an increased penalty on the aircraft performance compared to rigid foam insulation. Besides the criterion of minimal block fuel, the dormancy time is compared, indicating the thermal efficiency. Applying multilayer insulation, the dormancy time can be increased significantly calling for a discussion of operational requirements for hydrogen-powered aircraft

Preliminary Aircraft Design within a Multidisciplinary and Multifidelity Design Environment

In this paper, the preliminary aircraft design tool openAD is presented. Over the past years the DLR has developed a multidisciplinary and multifidelity design environment for aircraft design to evaluate and assess various concepts and technologies at aircraft level. Thereby, a valid and consistent design can be derived by a minimum set of top-level aircraft requirements. This design environment is highly modular where the domain specific tools are provided and hosted across the different DLR institutes. As part of the design process, openAD was developed as the key enabler for overall aircraft design and assessment

Mobilization of putative high-proliferative-potential endothelial colony-forming cells during antihypertensive treatment in patients with essential hypertension

Recent studies have shown that in response to vascular damage or ischemia, bone marrow-derived endothelial progenitor cells (EPCs) are recruited into the circulation. To investigate whether antihypertensive treatment has an influence on the number of circulating EPCs, patients with essential hypertension were treated either with the angiotensin receptor antagonist telmisartan, the calcium channel blocker nisoldipine, or their combination for 6 weeks. At baseline and after 3 and 6 weeks of treatment, EPCs were identified and quantified by fluorescence-activated cell sorting (FACS) analysis and by their capacity to generate colony-forming units of the endothelial lineage (CFU-EC) in a methylcellulose-based assay. During treatment, patients in the nisoldipine groups, but not in the telmisartan group, showed a significant mobilization of EPCs, which in part had the capacity to generate large-sized colonies comprising more than 1,000 cells. Moreover, a remarkable correlation between the number of CFU-EC and the number of circulating CD133(+)/CD34(+)/CD146(+) cells was observed, thereby providing strong evidence that cells with this phenotype represent functional EPCs. No correlation was found between the numbers of CFU-EC and the blood pressure levels at any time point during the treatment. Hence, nisoldipine-induced mobilization of EPCs might represent a novel mechanism by which this antihypertensive compound independently of its blood pressure-lowering effect contributes to vasoprotection in patients with essential hypertension

Analytical fuselage structure mass estimation using the PANDORA framework

Air traffic emissions have a significant impact on our environment and on the climate change. Since 2020, multiple research activities have been conducted at the German Aerospace Center (DLR) in the project “Exploration of Electric Aircraft Concepts and Technologies” (EXACT) to analyse the potential of eco-efficient aircraft concepts to reduce emissions. To handle the complexity on aircraft pre-design level, the usage of multidisciplinary design optimization (MDO) workflows and a common aircraft description format are an established procedure at DLR. The framework “Remote Component Environment” (RCE, [1]) is used to build MDO-workflows while the aircraft is described using the “Common Parametric Aircraft Configuration Schema” (CPACS, [2]). Different specific disciplines for aircraft design are part of the EXACT project to assess hybrid-electric aircraft concepts including the estimation of flight performance, loads and structural masses of the aircraft. At the Institute for Structures and Design (BT) the primary fuselage structural mass is estimated for different aircraft concepts using fast analytical methods based on the fuselage geometry, the definition of primary structures like frames and stringers and the application of cut-loads on the fuselage for different loadcases. This capability is implemented in the Python-based modelling and sizing framework called “Parametric Numerical Design and Optimization Routines for Aircraft” (PANDORA, [3]), which is under development since 2016. The PANDORA environment integrates developments like generating finite element (FE) models of aircraft based on CPACS parameters, converting FE models between different solver formats, creating and editing CPACS models and numerical as well as analytical sizing of aircraft models. In addition, more detailed FE models with different discretization approaches can be generated for crash and ditching simulations (EASN 2021 [4]). An overview of the PANDORA framework and some results of the EXACT project are given in this presentation