The Potential of Liquid Hydrogen for long range aircraft propulsion

The growth of aviation needed to cater for the needs of society might be undermined by restrictions resulting from the environmental implications of air traffic. Hydrogen could provide an excellent alternative to ensure a sustainable future for aviation. Several challenges remain to be addressed though before its adoption can become reality. The liquid hydrogen tanks are one of the areas where considerable research is needed. Further insight into unusual restrictions on aircraft classes that would be thought of as ideal candidates for hydrogen is also required. Hydrogen fueled very large long range transport aircraft for instance suffer from the 80 m airport box constraint which leads to a strong decrease in performance compared to other aircraft classes. In this work 3 main tools are developed to look into some of these issues. An aircraft conceptual design tool has been set up to allow a comparison between kerosene and hydrogen on a common and hence fair basis. An engine performance assessment routine is also developed to allow the coupling of the design of engine and aircraft as one integrated system. As the link between both subsystems is the liquid hydrogen tank, a detailed design method for the tanks has also been created. With these tools it has been shown that the gravimetric efficiency for large transport aircraft varies by only a few percent for a wide range of fuel masses and aircraft diameters with values in the order of 76to 80%. The performance of the long range transport aircraft itself however varies strongly from one class to another. For aircraft with a passenger load around 400 passengers, takeoff weight reductions around 25% can be obtained for similar operating empty weights and fuel weights of about 30% of the equivalent kerosene fuel weight. For 550 passenger aircraft however, the takeoff weight reduction reduces strongly due to the need for a triple deck fuselage and the resulting increase in fuselage mass. Whereas for the first category of aircraft, a 3 to 6 times higher fuel price per energy content can be afforded for similar direct operating costs, this cost advantage is reduced by about a third for the 550 passenger aircraft. A twin fuselage configuration alleviates the geometrical restrictions and restores the potential for an aircraft family but does not yield strong weight reductions. In a subsequent study, the implications of unconventional engine cycles as well as drag reduction resulting from natural laminar flow through surface cooling should be assessed using the developed set of tools as this will reveal the full potential of hydrogen as an aviation fuel

Implementation of an unloading compliance procedure for measurement of crack growth in pipeline steel

As the demand for fossil fuels increases, pipelines are constructed in inhospitable areas. Under these conditions, not only the strength but also the deformability of the pipelines becomes crucial. A strain based design (SBD) procedure needs to be established. Traditional stress based approaches to evaluate defect tolerance lead to conservative predictions. There is a need to accurately define the fracture toughness of the pipeline steel and assess the criticality of weld defects under strain based conditions. This paper focuses on the implementation of the unloading compliance method to determine stable crack growth. The standardized test procedure described in ASTM E1820 is applied. This method is a handy tool to obtain the J-resistance curves which can forecast ductile failure in pipeline girth welds. Preliminary experiments have been performed on Single Edge Notch Bend (SENB) specimens of plain pipe metal. Using the implemented procedure, it was possible to obtain a good fit between calculated and measured crack size. The most important result is the smoothness of the calculated crack growth and the rather monotonic increase of crack size. Since testing on SENB is well known to provide conservative measurements, Single Edge Notch Tension (SENT) specimens will be evaluated in future work

The potential of liquid hydrogen for long range aircraft propulsion

The growth of aviation needed to cater for the needs of society might be undermined by restrictions resulting from the environmental implications of air traffic. Hydrogen could provide an excellent alternative to ensure a sustainable future for aviation. Several challenges remain to be addressed though before its adoption can become reality. The liquid hydrogen tanks are one of the areas where considerable research is needed. Further insight into unusual restrictions on aircraft classes that would be thought of as ideal candidates for hydrogen is also required. Hydrogen fueled very large long range transport aircraft for instance suffer from the 80 m airport box constraint which leads to a strong decrease in performance compared to other aircraft classes. In this work 3 main tools are developed to look into some of these issues. An aircraft conceptual design tool has been set up to allow a comparison between kerosene and hydrogen on a common and hence fair basis. An engine performance assessment routine is also developed to allow the coupling of the design of engine and aircraft as one integrated system. As the link between both subsystems is the liquid hydrogen tank, a detailed design method for the tanks has also been created. With these tools it has been shown that the gravimetric efficiency for large transport aircraft varies by only a few percent for a wide range of fuel masses and aircraft diameters with values in the order of 76to 80%. The performance of the long range transport aircraft itself however varies strongly from one class to another. For aircraft with a passenger load around 400 passengers, takeoff weight reductions around 25% can be obtained for similar operating empty weights and fuel weights of about 30% of the equivalent kerosene fuel weight. For 550 passenger aircraft however, the takeoff weight reduction reduces strongly due to the need for a triple deck fuselage and the resulting increase in fuselage mass. Whereas for the first category of aircraft, a 3 to 6 times higher fuel price per energy content can be afforded for similar direct operating costs, this cost advantage is reduced by about a third for the 550 passenger aircraft. A twin fuselage configuration alleviates the geometrical restrictions and restores the potential for an aircraft family but does not yield strong weight reductions. In a subsequent study, the implications of unconventional engine cycles as well as drag reduction resulting from natural laminar flow through surface cooling should be assessed using the developed set of tools as this will reveal the full potential of hydrogen as an aviation fuel.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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

Structure and antagonism of the receptor complex mediated by human TSLP in allergy and asthma

The pro-inflammatory cytokine thymic stromal lymphopoietin (TSLP) is pivotal to the pathophysiology of widespread allergic diseases mediated by type 2 helper T cell (Th2) responses, including asthma and atopic dermatitis. The emergence of human TSLP as a clinical target against asthma calls for maximally harnessing its therapeutic potential via structural and mechanistic considerations. Here we employ an integrative experimental approach focusing on productive and antagonized TSLP complexes and free cytokine. We reveal how cognate receptor TSLPR allosterically activates TSLP to potentiate the recruitment of the shared interleukin 7 receptor a-chain (IL-7Ra) by leveraging the flexibility, conformational heterogeneity and electrostatics of the cytokine. We further show that the monoclonal antibody Tezepelumab partly exploits these principles to neutralize TSLP activity. Finally, we introduce a fusion protein comprising a tandem of the TSLPR and IL-7Ra extracellular domains, which harnesses the mechanistic intricacies of the TSLP-driven receptor complex to manifest high antagonistic potency

PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula

The JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate

PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar

(Abridged) We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the HII region to the atomic PDR (crossing the ionisation front (IF)), and the subsequent transition to the molecular PDR (crossing the dissociation front (DF)). We use high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science Program. The NIRSpec data reveal a forest of lines including, but not limited to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. We observe numerous smaller scale structures whose typical size decreases with distance from Ori C and IR lines from CI, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the PDR. The H2 lines reveal multiple, prominent filaments which exhibit different characteristics. This leaves the impression of a "terraced" transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $\mu$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $\mu$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&

Cryogenic hydrogen fuel tanks for large hypersonic cruise vehicles

The design of light yet highly insulated cryogenic tanks is a key enabling technology for hydrogen-fuelled flights, especially when operation in the harsh thermal environment associated with hypersonic speeds is envisaged. This paper examines the use of different insulation systems for cryogenic hypersonic tanks. The investigation for a Mach 5 flight shows that a combination of foam and fully load-bearing aerogel blanket leads to the lightest tank, with a gravimetric efficiency of 73%. If the aerogel blanket cannot be strengthened sufficiently so that it can bear the full load, then a combination of foam and fibrous insulation materials gives the best solution with a gravimetric efficiency of 70.3%. This is around 10% better than (non-load-bearing) aerogel or multi-layer insulations. However, the performance of the foam-fibrous insulation is more sensitive to the external skin temperature than that of other insulation materials so that a foam-multilayer insulation system becomes more efficient at speeds beyond Mach 9. This demonstrates that it is critical to make the best use of each material and that proper combinations of materials can considerably improve the performance of the insulation system.SCOPUS: ar.jinfo:eu-repo/semantics/publishe