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Because the respiration processes contributing to the elimination of organic chemicals deviate between air- and water-breathing organisms, existing and widely used procedures for identifying chemicals not subject to bioaccumulation in aquatic organisms based on the octanol-water partition ratio K OW need to be complemented with similar procedures for organisms respiring air. Here we propose such a procedure which relies on the comparison of a compound's predicted KOW , octanol-air partition ratio KOA and biotransformation half-lifeHLB with three threshold values, below which elimination is judged to be sufficiently rapid to prevent bioaccumulation. The method allows for the consideration of the effect of dissociation on the efficiency of urinary and respiratory elimination. Explicit application of different types of the prediction error, such as the 95 percent prediction interval or the standard error, allows for variable tolerance for false negative decisions, i.e., the potential to judge a chemical as not bioaccumulative even though it is. A test with a set of more than 1000 diverse organic chemicals confirms the applicability of the prediction methods for a wide range of compounds and the procedure's ability to categorise approximately four fifth of compounds as being of no bioaccumulation concern, suggesting its usefulness to screen large numbers of commercial chemicals to identify those worthy of further scrutiny. The test also demonstrates that a screening based solely on KOW and KOA would be far less effective, because the fraction of chemicals that can be judged as sufficiently volatile and/or sufficiently water soluble for rapid respiratory and urinary elimination based on the partitioning properties predicted for their neutral form is relatively small. Future improvements of the proposed procedure depend largely on the development of prediction methods for the biotransformation kinetics in air-breathing organisms and for the potential for renal reabsorption. This article is protected by copyright. All rights reserved.

The oxygen reduction electrocatalysis is a key reaction for energy technologies such as fuel cells and air breathing batteries for which development of stable and efficient electrocatalysts remains a substantial challenge, especially when excluding precious metals. Multi-component metal oxides are complex materials that offer opportunities for catalyst development and challenges for prediction of optimal compositions. We use high throughput synthesis and electrochemistry to explore metal oxide electrocatalysts containing 1 to 4 of the elements Mg, Ca, Mn, Fe, Ni, Y, In, and La. Mining the resulting dataset of 7798 unique metal oxide compositions guides additional activity and stability experiments that reveal multiple avenues for further catalyst development based on (i) stabilization of Mn through incorporation in Mn-Ni–Fe oxides, (ii) discovery of Ni–Fe-La oxide electrocatalysts with excellent stability, and (iii) discovery of Mn-Ni–Fe-La oxide electrocatalysts that optimize activity while retaining excellent operational stability.

A key parameter that determines the efficiency of proton exchange membrane fuel cells is their operating conditions. Optimization of various components in these fuel cells is pivotal in improving cell performance, as their performance is directly related to the operational conditions the cells are subjected to. This investigation examined the viability of an air breathing fuel cell subjected to ambient conditions in Riyadh in Saudi Arabia. A validated three-dimensional air breathing 5-cell stack, modelled in ANSYS was utilised to generate the results. Furthermore, the work also considered the feasibility of deploying a humidifier unit for the hydrogen inlet, so as to ascertain the physical behaviour of the PEMFC stack. It was observed that the performance of the stack reaches its peak during the summer time (June–August), and hydrogen humidification improves output performance by 40%.

Based on the equal-intensity shock theory, this article designed a supersonic inlet working in Mach number 3.0∼5.5 with the background of an air-breathing engine. The inlet applied the four-shock train mixed compression configuration and inserted a sidewall compression at the beginning of the isolator. Through developing effective 3D RANS computations validated by current experiments, the performance of the designed inlet was identified. The designed inlet self-starts at freestream Mach number Ma∞ = 3.0 under which the total pressure recovery coefficient has dramatic increment, and the aerodynamic choking at the inlet throat no longer presents; the inlet keeps working at all studied flight states with zero angle of attack (AoA) and achieves shock-on-lip at the design point Ma∞ = 5.0. Both positive and negative AoAs can disrupt the equal-intensity shock allocations, which degrade the inlet performance. The inlet obtains maximum total pressure recovery coefficient at zero AoA. The maximum back pressure at Ma∞ = 3.0∼5.5 obtained by the inlet surpasses the requirements and keeps a certain margin. The inlet performance basically meets all the goals proposed by the engine.

This paper proposes a novel fixed-time adaptive general type-2 fuzzy logical control (FAGT2FLC) scheme for an air-breathing hypersonic vehicle (AHV) with uncertainties. Firstly, the AHV dynamic model is transformed into a strict feedback form. Then, the FAGT2FLC is designed based on the transformed model to improve robustness and guarantee fixed-time convergence of the closed-loop system. The general type-2 fuzzy logic system (GT2FLS) is utilized to approximate the model uncertainties; for the purpose of designing adaptive laws, the [Formula: see text]-plane method is employed to represent the GT2FLS. A parameter projection operator is used to solve the possible singularity problem of parameter adaption. Besides, a fixed-time differentiator is used to deal with the “explosion of terms” inherent in backstepping method. Theoretical analysis based on relevant lemmas shows that the closed-loop system will converge into a small error band in fixed time. Lastly, detailed simulations are carried out to demonstrate the effectiveness and superiority of the proposed control scheme.

The obligate air-breathing Amazonian fish, Arapaima gigas, hatch as water-breathing larvae but with development, they modify their swim bladder to an air-breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO. By using a variety of methods, we quantified the surface area and diffusion distances of the gills and skin, and the swim bladder volume and anatomical complexity from hatch to 11-week-old juveniles. In addition, we identified the presence of two ionocyte types in the gills and show how these change with development. Until 1.6 g, A. gigas possess only the H+ -excreting/Na+ -absorbing type, while 5-g fish and adults have an additional ionocyte which likely absorbs H+ and Cl- and excretes HCO3- . The ionocyte density on the gill filaments increased with age and is likely a compensatory mechanism for maintaining ion transport while reducing gill surface area. In the transition from water- to air-breathing, A. gigas likely employs a trimodal respiration utilizing gills, skin, and ABO and thus avoid a respiratory-ion regulatory compromise at the gills.

This paper presents a performance analysis on a novel engine concept, currently under development, in order to achieve hybrid air-breathing rocket technology. A component-level approach has been developed to simulate the performance of the engine at Mach 5, and the thermodynamic interaction of the different working fluids has been analysed. The bypass ramjet duct has also been included in the model. This facilitates the improved evaluation of performance parameters. The impact of ram drag induced by the intake of the engine has also been demonstrated. The whole model is introduced into a multi-platform application for aeroengine simulation to make it accessible to the interested reader. Results show that the bypass duct modelling increases the overall efficiency by approximately 7%. The model calculates the specific impulse at approximately 1800 seconds, which is 4 times higher than any chemical rocket.

Many hypoxic freshwater springs have become havens for air-breathing, invasive, loricariid armored catfish. However, this does not seem to be the case for juvenile catfish, which are rarely seen. We wondered if hypoxia and air-breathing influenced habitat selection in juveniles, and so we designed an experiment to test the sensitivity of two size classes of juvenile catfish to varying concentrations of dissolved oxygen. Small and medium-sized juvenile Pterygoplichthys sp. were exposed to hypoxic, transitional, or normoxic conditions in the laboratory, and their air-breathing rates were measured and compared between fish size and dissolved oxygen category using a two-way ANOVA. We also measured air-breathing synchrony, which was assessed with a coefficient of dispersion and compared between fish sizes with a two-tailed, one-sample t-test, and with dissolved oxygen using linear regressions. We found that all fish air-breathed significantly more frequently under hypoxic conditions and smaller fish breathed significantly more frequently than medium fish at all dissolved oxygen levels, although there was no interaction effect. There was no air-breathing threshold oxygen tension, and only small fish exhibited synchronous air-breathing behavior. All of the behavioral changes we observed as dissolved oxygen decreased would put juveniles at greater risk of predation, and likely explains why so few juveniles are found in hypoxic waters.

In practical combat scenario, the cooperative intercept strategies are often carefully designed, and it is challenging for the hypersonic vehicles to achieve successful evasion. Based on the analysis, it can be found that if several Successive Pursuers come from the Same Direction (SPSD) and flight with a proper spacing, the evasion difficulty may increase greatly. To address this problem, we focus on the evasion guidance strategy design for the Air-breathing Hypersonic Vehicles (AHVs) under the SPSD combat scenario. In order to avoid the induced influence on the scramjet, altitude and speed of the vehicle, the lateral maneuver and evasion are employed. To guarantee the remnant maneuver ability, the concept of specified miss distance is introduced and utilized to generate the guidance command for the AHV. In the framework of constrained optimal control, the analytical expression of the evasion command is derived, and the constraints of the overload can be ensured to be never violated. In fact, by analyzing the spacing of the pursers, it can be classified whether the cooperative pursuit is formed. For the coordination-unformed multiple pursers, the evasion can be achieved lightly by the proposed strategy. If the coordination is formed, the proposed method will generate a large reverse direction maneuver, and the successful evasion can be maintained as a result. The performance of the proposed algorithms is tested in numerical simulations.

This paper investigates the design problem of the attitude controller for air-breathing supersonic vehicle subject to uncertainties and disturbances. Firstly, the longitudinal model is established for the attitude controller design which is devised as a strict feedback formulation, and a transformed tracking error is derived with the prescribed performance control technique such that it can limit the tracking error to a predefined region. Then, a novel linear active disturbance rejection control scheme is proposed for the attitude system to enhance the steady-state and transient-state performances by incorporating the transformed tracking error. On the basis of the Lyapunov stability theorem, the convergence and stability characteristics are both rigorously proved for the closed-loop system. Finally, extensive contrast simulations are conducted to demonstrate the effectiveness, robustness, and advantage of the proposed control strategy.

Low oxygen concentration is a common feature occurring in a wide range of aquatic systems and in varied ranges depending upon temporal frequency, seasonality and persistence of a place. There have always been naturally occurring low oxygen condition in freshwaters of tropical countries like India. Moreover, anthropogenic activities, related primarily to organic and nutrient enrichment, have led to increase in hypoxia and anoxia both in fresh and in marine system. The fishes in a tropical country like India are quite frequently exposed to this. Aquatic organisms which are frequently exposed to hypoxia show adaptations at all the three levels, namely behavioural, morphological and physiological. To assess the effect of hypoxia at physiological level, change in anaerobic and aerobic enzyme activities and protein profiling in selected tissues of air-breathing catfish, Heteropneustes fossilis, was undertaken. Fish were exposed to experimentally provoked hypoxia for different durations and were killed to study the effect of hypoxia on selected enzymes activities in heart, liver, brain and muscle. Significant changes were recorded. The observations indicated that different tissues respond differently to the stress of hypoxia and the enzyme activity responds in a tissue-specific manner.

Indiscriminate use of insecticides has increased many folds in the recent times. Farmers for the better yield of crops, are widely utilising the pesticides.

Accessory respiratory is generally accepted to have evolved independently on numerous occasions in adaption to aquatic hypoxia in freshwater habitats. In general, the air-breathing organ in fish is believed to be structurally modified to supplement respiration. In this study, intuitive evidence for elaborate structural modifications of the intestine, an air-breathing organ in mud loach (Misgurnus anguillicaudatus), compared with two other obligate aquatic breathers, grass carp (Ctenopharyngodon idellus) and yellow catfish (Pelteobagrus fulvidraco), were directly provided by histological and morphometric methods. As a result, a sharply decreasing height of mucosal folds and thickness of muscularis were manifested in loach intestine from its anterior to posterior region. Compared with grass carp and yellow catfish, loach had the smallest ratios of mucosal fold height/muscularis thickness to intestinal lumen radius in the posterior intestine. These suggested that the posterior intestine is the air-breathing location for the loach. Furthermore, length density of capillary (0.46±0.05 μm−2) in the posterior intestine of the loach was significantly higher than those of grass carp and yellow catfish. Meanwhile, diffusion distance of air-blood barrier (1.34±0.04 μm) in the posterior intestine of the loach was significantly smaller than those of the other two fish species. In summary, the characteristics of highly vascularized, short diffusion distance of air-blood barrier, thinned and flattened made the posterior intestine a perfect air-breathing location for the loach.

In the late twentieth century, tremendous use of second-class organophosphate insecticides especially chlorpyrifos (CPF) resulting into heavy accumulation in different non-targeted aquatic species ...

The structure and dynamic of the shock train in a mixing duct are investigated experimentally in a supersonic air breathing wind tunnel. High-speed schlieren technique and pressure measurements are utilized for the data acquisition. Nozzle clapboards are applied to separate the incoming flow into upper secondary flow, primary flow, and lower secondary flow. The Mach number of all incoming flows is 2.05, whereas the static pressures between primary and secondary flow stay unmatched. Experimental results indicate that nozzle clapboards lead to complex background waves and mixing layers in the mixing duct. As the throttling valve rotates at a constant speed, two motion patterns alternatively govern the shock train movement, namely jump movement and slow movement. Judging from the path of shock train leading edges, adverse pressure gradient at the wall of background flow induces jump movement, while the slow movement only appears at the zone of favorable pressure gradient. Besides, leading shock structures continuously change in the forward propagation process. Four types of leading shock structures are discovered namely regular reflection, convex-stem Mach reflection, straight-stem Mach reflection, and concave-stem Mach reflection. Based on the numerical results of the background flow field, these special structures are explained theoretically by analyzing the variation of the wavefront Ma contour lines.

This paper investigates a fast-tracking controller with prescribed performance for flexible air-breathing hypersonic vehicles subject to uncertain parameters, external disturbances, actuator faults and backlash non-linearity. For the velocity and altitude dynamics, a prescribed performance control scheme is respectively utilized to provide preselected bounds on the transient and steady characteristics of tracking errors, also it can effectively relieve the constraint of scramjet on the angle of attack. A sliding mode exact observer is introduced to estimate the lumped disturbance, meanwhile the analytic differential computation on virtual controllers is avoided in the back-stepping design for altitude tracking. Based on prescribed performance control and sliding mode exact observer, the non-singular fast terminal sliding mode technology is introduced to design a control law, which is capable of ensuring both velocity and altitude tracking errors converge into the prescribed sets in finite-time. Simulations on the high-fidelity air-breathing hypersonic vehicle mode are implemented to highlight the effectiveness of the developed controller.

A novel anti-saturation robust control algorithm (NARC) is presented for flexible air-breathing hypersonic vehicle (FAHV) with actuator saturation, including two controllers designed for velocity and height subsystem respectively. Firstly, an anti-saturation finite-time dynamic inversion controller is designed for velocity subsystem, in which an anti-saturation fixed-time compensator (ASFC) is proposed to ensure the stability of saturated system and make it exit saturated region faster. Compared with conventional anti-saturation compensator, the auxiliary variable of ASFC can converge with faster speed and higher precision when actuator is not saturated, which avoids the impact on original system. Secondly, an anti-saturation robust command filtered backstepping controller is designed for height subsystem, combining backstepping control, ASFC and a novel fixed-time filter (FTF). Compared with low pass filter, the FTF proposed can track input signal with faster response speed and higher precision without the need to select a smaller time constant, so as to avoid introducing high-frequency noise. Meanwhile, convergence domain of height subsystem can be reduced as well. Ultimately, simulations on FAHV with actuator constraints, parametric uncertainties and external disturbances are performed using the NARC and conventional anti-saturation controller respectively to demonstrate the superiority of NARC.

Lean fuel burning is considered as one of the most prominent methods to achieve the low temperature combustion reduces nitrogen oxides (NOx) emissions. However, as a result lean burning suffers from strong flame instabilities and a very lean operating condition near to the flame quenching limit is associated with the high risk of lean blowout (LBO) which has to be avoided. Therefore, the capability to sense the origin of LBO will provide substantial settlements to improve combustor reliability in order to achieve optimum performance, to extend engine life and to reduce maintenance cost. From the last few decades, many engine manufacturers and research institutions are working on the novel approaches based on the lean combustion concepts. For achieving desired objects, several passive control technologies were studied to improve the flame stabilization by modifying the injector geometry or flame holders in a permanent way. Adding to this, Non thermal plasma assisted combustion (NTPAC) technology is the most encouraging techniques to actively control the control the flow and combustion dynamics in consonance with real-time operating conditions without altering the combustor design. NTPAC improves the efficiency of combustors, increases flame stabilization, enhances low temperature oxidation, and extends the LBO limits, in the meantime it also reduces the significant amount of nitrogen oxides (NOx). From literature review it has been concluded that the effects of NTPAC is broadly classified into three ways: thermal effects, kinetic effects, and transport effects. Among all the NTPAC technologies, the dielectric barrier discharge (DBD) is widely considered and credit goes to the simplicity of its design and the wide range of operating modes.However, the effects of NTPAC on flame stability and LBO limits are not clearly understood yet, due to the complexity of each specific process involves in the plasma combustion. Therefore, for the better understanding of NTPAC processes, an experimental study was performed which investigates the behavior of premixed methane/air flames close to LBO limits at different operating conditions using plasma assisted lifted swirl combustor. The combustor was equipped with ring-needle shaped plasma actuator operated by sinusoidal generator at the maximum frequency of 20 kHz directly coupled with flame near to the nozzle. The test system was covered by faraday cage to avoid interference of electromagnetic fields produced through plasma discharge. The plasma actuator configuration involves a tungsten needle having a diameter of 1 mm and length equal to 46 mm. The needle was placed at the center of nozzle which referred as a high voltage (HV) electrode. However, the nozzle was acted as a grounded (GND) electrode. Electrical characterization of combustion characteristics was performed at different plasma actuation conditions and air/fuel mass flow rates. Flame behavior was also captured by high resolution CCD camera by predicting the recirculation zone produced by plasma, have the benefits of generating compact flames and allowing the high reaction rates. Acoustic measurements were performed using high sensitivity microphone. Furthermore, post processing of the microphone data involved application of Fast Fourier Transform (FFT).

In jet engines, turbine blades are exposed to particularly harsh conditions downstream of the combustion chamber. High temperature flows can be tempered via effusion cooling. Cooling flow rates are typically high, with velocity ratios VR = Uf /U? ranging from 100% to 300%, where Uf and U? are the characteristic velocities of the film and the incoming flow, respectively (see review in [1]). In order to minimise cooling flow rate while maintaining the integrity of the film, the effusion film must be precisely tailored. This requires a better understanding of the mixing processes at play between the injected film and the incoming boundary layer. To that end, this study uses a canonical turbulent boundary layer injected with an isothermal effusion film and focuses on a range of low velocity ratios VR 40%. Experiments are performed at large scale and low speed so as to acquire high resolution data. Data sets are obtained using Particle Image Velocimetry, visualisations, hot-wire measurements and pressure taps. Power spectral densities show a signature consistent with high Reynolds number boundary layers for the reference case VR=0%.Small-scale turbulence remains confined to the roughness sublayer, while very large-scale motions encompass the whole boundary layer up to the log region. The introduction of the effusion film increases turbulence near the wall at all scales up to VR ? 15 ? 20%. Above that critical blowing ratio the film separates, which prevents the large-scale motions from reaching the inner layer. This intensifies the large-scale fluctuations around y ? 0.1?, that is, just above the newly formed film. The amplitude modulation of small-scale turbulence by large-scale motions has been shown to be a relevant model of the inter-scale exchanges in high Reynolds number wall-bounded flows. This approach relates to the correlation between the large-scale motions and the large-scale envelope of small-scale fluctuations [2], namely the modulation coefficient AM. Often restricted to temporal correlations of hot-wire measurements, analyses based on the AM coefficient has recently been extended to spatial correlations [3, 4]. The present work uses the same approach to investigate the effect of the effusion film on the inter-scale exchanges. Below the critical VR, modulations of small-scale turbulence are enhanced but remain confined near the wall. With increasing VR, the separation of the effusion film causes the amplitude modulation to occur much further from the wall in the log layer at a much higher level. Such an evolution of AM is reminiscent of adverse pressure gradient boundary layers, which exhibit a similar separation of the inner sub-layer [5]. References [1] Krewinkel R., A review of gas turbine effusion cooling studies, Int. Journal of Heat and Mass Transfer 66: 706722, 2013. [2] Mathis R., Hutchins N. and Marusic I., Large scale amplitude modulation of the small scale structures in turbulent boundary layers, J. Fluid Mech. 628: 311337, 2009. [3] Basley J., Perret L. and Mathis R., Spatial modulations of kinetic energy in the roughness sublayer, J. Fluid Mech. 850: 584610, 2018. [4] Yao Y. C., Huang W. X. and Xu C. X., Amplitude modulation and extreme events in turbulent channel flow, Acta Mech. Sin, 31(1): 19, 2018. [5] Harun Z., Monty J. P., Mathis R. Marusic, I., Pressure gradient effects on the large-scale structure of turbulent layers, J. Fluid Mech., 715: 477498, 2013.

The operating environment of jet turbines is subject to high fluid temperature which often results in blade dilation and, consequently, a rubbing phenomenon between the blades and the stator. This paper proposes a condition monitoring strategy based on strain measurements. A mathematical model is first proposed to describe the response of the rub signal. This model is then used to de-noise the signal from interfering noises and eventually construct relevant condition indicators for each of the turbine blades rubs. The proposed technique is validated on real signals captured from a strain gauge mounted on the stator of a turbomachine.

Dynamics of a shock wave train induced by downstream flow oscillations Erwin BEKAERT, Aurelien GENOT, Thomas LE PICHON DMPE, ONERA, Universite Paris Saclay, 91123 Palaiseau, France erwin.bekaert@onera.fr, aurelien.genot@onera.fr, thomas.le_pichon@onera.fr Thierry SCHULLER Institut de Mecanique des Fluides de Toulouse, Universite de Toulouse, CNRS, 31062 Toulouse, France thierry.schuller@imft.fr The ramjet is an air-breathing propulsion system well-adapted for supersonic speeds, between Mach 2 and Mach 5. As for other propulsion systems, its extreme operating conditions may facilitate the triggering of thermoacoustic instabilities which can lead to premature extinctions or chamber damages. Thermoacoustic instabilities have been experimentally identified in the ONERA experimental bench \"Research Ramjet\" (Statoreacteur de Recherche (SdR)). The SdR has been designed in order to examine the basic physical phenomena governing the flow dynamics and build up an experimental database as a mean to assess and validate numerical flow simulations. The SdR is a two-inlet side-dump combustor, which can be operated with gaseous or liquid fuels for operating conditions that are representative of flight conditions. This combustor was designed for direct-connected tests. Consequently, the air inlets shown on the setup in Fig. 1 have been simplified compared to a flight vehicle ; however, as in real diffusers, pseudo shocks develop downstream the sonic throats. Self-sustained combustion oscillations were found to be coupled to two acoustic longitudinal modes taking place inside the combustor and the air-inlet inlet cavities [1]. When acoustic oscillations propagate upstream inside the air inlet, they are reflected by the shock wave train downstream the sonic throat leading also to a cyclic displacement of this structure inside the flow. This in turn leads to a change of the volume and acoustic characteristic length over which the acoustic mode develops. These modifications intensely alter the flow dynamics and therefore, the combustion inside the chamber. In order to model the unsteady behavior of the combustor, it is necessary to characterize the motion and the response of the shock wave train inside the air inlet when it is submitted to flow oscillations. See Abstract file Figure 1: Schematic of the ONERA Research Ramjet and the studied zone encircled by dotted lines Large-eddy simulations with the ONERA flow solver CEDRE [2] are conducted to analyze the pseudo-shock response to acoustic perturbations and its motion when it is submitted to downstream pressure oscillations. The numerical setup only considers the air inlet pipe shown in Fig. 1. Pressure disturbances are simulated by imposing a sinusoidal signal at the numerical domain outlet. The amplitude and the frequency of the forcing are varied. Results for the dynamics of the shock wave train are compared to analytical models developed for normal shocks [3, 4]. References [1] A. Roux. Simulation aux grandes echelles dun statoreacteur. 2009. [2] A. Refloch, B. Courbet, A. Murrone, P. Villedieu, C. Laurent, P. Gilbank, J. Troyes, L. Tesse, G.Chaineray, J-B. Dargaud, E. Quemerais, and F. Vuillot. CEDRE software. Aerospace Lab., vol. 2, Paper number AL02-11, 2011. [3] F.E.C. Culick and T. Rogers. The response of normal shocks in diffusers. AIAA J., Vol. 21, No. 3, pages 13821390, 1983. [4] M. Sajben. Response of normal shocks in diffusers. AIAA J., Vol. 23, No. 3, pages 477478, 1985.

Two mathematical models have been built for air-breathing and conventional polymer electrolyte fuel cells to explore the reasons affecting the cell performance. A parametric study has been conducted to (i) investigate how each type of fuel cells responds to changes in some key parameters and (ii) consequently obtain some insights on how to improve the performance of the air-breathing fuel cell. The conventional fuel cell significantly outperforms the air-breathing fuel cell and this is due to substantially higher forced convection-related heat and mass transfer coefficients associated with the conventional fuel cell as compared with natural convection-related heat and mass transfer coefficients associated with airbreathing fuel cell. The two types of fuel cell respond differently to changes in porosity and thickness of gas diffusion layer: the conventional fuel cell performs better with increasing porosity of gas diffusion layer (from 0.4 to 0.8) and decreasing thickness of gas diffusion layer (from 700 to 100 mm) while the airbreathing fuel cell performs better with decreasing porosity and increasing thickness of gas diffusion layer. Further, the air-breathing fuel cell was found to be more sensitive to membrane thickness and less sensitive to electrical resistance compared to conventional fuel cell.

The Air Cooled Oil Cooler (ACOC) heat exchanger is an important element of the lubrication system of aero engines. The aim of the lubrication system is to cool and to lubricate the bearings and gears of the engine to ensure its proper working. The ACOC heat exchanger is complementary to another heat exchanger in the lubrication system, the Fuel Cooled Oil Cooler (FCOC) which cooles the oil by exchanging its heat to warm up the fuel before the injection. But there is a maximal temperature for fuel before the injection. Therefore an ACOC heat exchanger is placed in the system to extract the excess temperature of the oil.\\\\ The Aero-Thermo-Mechanics department of the Universit\\\'{e} libre de Bruxelles (ULB) has developed two test set-ups for the charaterisation of ACOC prototypes: a low air flow rate set-up for the experimental testing of small scale ACOC prototypes and a higher air flow rate set-up for real scales prototypes and more realistic flight conditions. The two test benches are complementary. The low air flow rate set-up is able to deliver a maximum air flow rate of 250 g/s based on a blowdown system with a 40 bar air tank \\cite{ref1}. The larger air flow facility can performed experimental campaigns on larger matrices of Additive Layers Manufacturing (ALM) ACOC prototypes. This test set-up is able to reach a maximum air mass flow rate of 700 g/s at a surpression of 1 bar. One of the particularities of the two test rigs is the control of the temperature of the air at the inlet of the ACOC heat exchanger. The air flow can be heated at a required temperature. In the test section of the air line multiple sensors are set in order to characterise the air flow at the inlet and the outlet of the prototypes. The oil circuit is similar in the two benches. It is composed of a tank, an oil heater, a pump and various sensors. The temperature of the oil can be controlled to a required value up to 200 $^\\circ$C. The objectives of the different experimental campaigns on this test rig are to measure the air pressure drop due to the ACOC heat exchanger, the thermal efficiency and the air velocity profiles at the inlet and the outlet of various prototypes for different air flow rates \\cite{ref2}. \\\\ The paper will present the two benches in more details and the different air and oil conditions that can be obtained in the benches. The oil part or the air part of the two test benches can be operated separately.

In many engineering applications, there are numerous undesirable objects which are generally known as Foreign Object because of their dangerous effects. Dust, sand, stones, salt spray, birds, ice, snow and metal parts are very usual examples of foreign object for helicopters [1]. Especially sand and dust are the most common foreign object sources which are responsible from the compressor erosion due to large number of dangerous operation areas. Inertial particle separator (IPS) is a device located at the frontmost of an engine which is designed to protect it from these foreign objects. It provides protection by deflecting both air and particle flows outward direction, where dust/sand particles, which has higher inertia, move into the scavenge part and air, which has lower inertia, turn back to the core of the engine. When an engine with an integrated IPS is installed on a helicopter, a suitable intake design is needed to satisfy the required airflow. There are several parameters that affects characteristics of the IPS flow due to intake designs such as distortion and swirl. Moreover, compressor rotation, helicopter attitudes (sideslip and pitch angle), rotor interactions and gust affect the swirl type (bulk, twin and offset swirl), angle, and direction in conjunction with the intake design. In the literature, all studies assume that the incoming flow to the IPS is uniform and straight, however this is not true for installed engines. In this study, only bulk swirl effects on the IPS performance is investigated in terms of efficiency by using computational fluid dynamics (CFD). Computational method is validated with an experimental data [2], which has 2% uncertainty, with an error less than 3% at low ? (scavenge to core air mass flows ratio). CFD analyses are performed with Star-CCM+ software at Linux based high performance computing (HPC) cluster by using unsteady approach and turbulence is modeled with Improved Delayed Detached Eddy Simulation (IDDES) model. Lagrangian approach is used to simulate particle motion with one-way coupling option. Changes in flow properties due to particle motion is so small hence, it is neglected. Particles are modelled as spherical and Schiller-Naumann correlation is used for drag force estimation. After the validation, a 3-D annular IPS geometry is created by using Siemens NX; however, only the 24 slice of this geometry is analyzed to reduce computational power. Flow domain is discretized with 8 million hexahedron volume elements. It is important to note that this is the first multi-phase unsteady analysis of a 3-D annular IPS geometry with the most accurate simulation approach [3]. 15 bulk swirl is given as an input from the intake boundary in addition to the incoming flow. Pressure outlet boundary with target mass flow rate option is used at the end of scavenge and core parts. Results show that, 1% increase in efficiency is obtained with 15 swirling flow for ? = 0.16 by using ISO-12103 A4 course sand distribution. Similar studies are going to be performed for ? = 0.10 and ? = 0.20 and their results are going to be shared later.

Scramjets are of growing interest for their application in defense and space explorations [1], [2]. Research on supersonic combustors is of significant importance for the development of scramjets. To have sustainable stable thrust, the flame should stabilize within the combustor and have minimum ignition delay. The flame stabilization in the supersonic combustor is highly transient in nature. Hence, a significant amount of research is focused on ignition and flame stabilization in supersonic combustors[3]. Different stabilization modes can exist in a supersonic combustor. These combustion modes are sensitive to parameters such as injection method, injection pressure, and equivalence ratio (ER). Therefore, the current research aims to study the transient nature of flame stabilization in a strut stabilized supersonic combustor. The experiments are performed using H2-O2 combustion to vitiate the air to stagnation properties of 1450K and 8 bar. The H2 fuel is injected into an M 2.5 flow through ten 2.5 mm holes on either side of a strut. High-speed flame imaging is used to detect the flame transitions between two modes. Simultaneous OH* chemiluminescence and OH PLIF imaging are used to study the flame structure at the strut. For low ER, the flame anchors at the wake of the strut. The recirculation zone at the base of the strut provides free radicals and hot products for the flame to be stabilized at the wake. The region of heat release is observed in the recirculation zone and the shear layer using OH* chemiluminescence images. As the ER increases, the flame flashes back and stabilizes at the fuel jet. As the ER increases the strength of the injection shock increases, thereby decreasing the local velocity and increasing the static temperature, which in turn increases the flame speed of the mixture. Thus, the flame flashes back to the fuel jet. The flame is stabilized at the jet wake by the free radicals and hot products supplied to it by the horseshoe vortices produced by the jet. The post flame structure at the wake of the strut is studied using 10 Hz OH PLIF imaging. The presence of OH radicals in the wake indicates the availability of the hot products that will be supplied to stabilize the flame. Hence the flame is stabilized at the strut wake even at very low ERs. The paper summarizes the transient behavior of flame stabilization in a supersonic combustor.

The aviation industry has made great progress in continuous improvements that reduce the key pollutants associated with aero engines. However, high demands on the aviation industry drive manufacturers and designers to develop even more efficient aero engines. The introduction of a geared turbofan engine was a breakthrough, although it created new challenges for suppliers and designers. Due to the continuous development of the modern geared and ultra-high bypass ratio turbofan engines, individual components such as Turbine Rear Structure (TRS) should be optimized in terms of weight, total thrust and aerodynamics. The aerodynamic performance of a TRS is affected by the inflow from the low-pressure turbine (LPT) due to the presence of the stator and rotor wakes (Fig. 1) and their evolution that can lead to pressure redistribution and additional pressure losses. Therefore, more detailed aerodynamic study of LPT wakes is needed to fully understand their influence on aerodynamic performance. This paper presents the results from PIV and hot-wire experimental campaigns, conducted for the first time in a turbine facility at Chalmers that provides engine-realistic boundary conditions for the TRS. The hot-wire technique has been used to capture stator wakes and its development through the volume between adjacent outlet guide vanes (OGVs) located downstream LPT. Ensemble averaging was performed, and data is presented in the form of mean and standard deviation of ensemble averaged velocity. A non-intrusive 3C-2D PIV measurements were acquired for the region between LPT and OGVs enabling the determination of important inflow characteristics. PIV gave as an output the instantaneous flow field. Experimental data from both campaigns was obtained at aerodynamic design point with constant Reynolds number. The results from standard deviation velocity contours clearly reveal stator wakes inside the measurement volume. The presence and downstream evolution of the stator wakes is shown to affect the flow in the TRS leading to total pressure redistribution and influencing pressure losses downstream OGV. Through PIV, the instantaneous velocity and vorticity flow fields for the inlet plane located upstream OGV were obtained. In the measured velocity field, the rotor wake regions with a velocity deficit were identified. For the present operating conditions, the analysis of instantaneous velocity fields indicates that rotor wakes originated from the LPT are composed of small-scale vortices no larger than 5-10 mm in size. To conclude, the outcome of the experimental campaigns can be deemed largely satisfactory, with obtained for the first time experimental data for understanding of the complex unsteady flow structures in the LPT-TRS.

The growing interest in reusable Single-Stage-To-Orbit (SSTO) launchers establishes the necessity to develop a suitable propulsion system, able to provide an effective alternative to conventional thermochemical rocket launchers. Among all the technologies proposed over the years, Rocket Based Combined Cycles (RBCC) appear as the most attractive choices for this purpose. A specific, promising application is the deeply precooled Synergetic Air-Breathing Rocket Engine (SABRE), which uses sub-cooled liquid hydrogen as its fuel and sub-cooled liquid oxygen as the oxidiser in rocket mode. In rocket mode the engine operates as a closed cycle; in air-breathing mode the liquid oxygen flow is replaced by atmospheric air. The airflow is compressed by an axisymmetric intake and is cooled by a pre-cooler heat exchanger to cryogenic temperatures. The pre-cooler heat exchanger is an element of a closed cycle helium loop which uses the hydrogen fuel as the heat sink before it enters the combustion chamber. In the combustion chamber fuel mixes with air, which has been compressed after cooling. This engine is proposed to propel the spaceplane SKYLON to over Mach 5 at an altitude of 25 km. The SABRE/SKYLON system is capable of placing into an equatorial low Earth orbit a 12 tonnes payload, at a gross takeoff mass of 275 tonnes. The proposed air-breathing solution significantly reduces the subsequent less efficient rocket phase of the ascent trajectory to low earth orbit. The aim of this paper is to perform a preliminary comparison between a RBCC engine, the SABRE solution and a conventional rocket baseline for a Low Earth Orbit mission. Due to the lack of data available, performance computation is based on simplified models. RBCC engine numerical model is developed on the basis of the approach presented in 1, providing an analysis tool that gives thrust, specific impulse and specific fuel consumption for given flight conditions and geometry of the engine, which is here selected to be the one of the propulsion system designed for Hyperion SSTO 2. A hypothetical constant dynamic pressure trajectory is selected to compute performance parameters according to flight altitude and Mach number during airbreathing propulsion phase. RBCC engine works in three different airbreathing modes: ejector up to Mach 2, ramjet between Mach 2 and 5 and scramjet between Mach 5 and 10. The SABRE engine is modelled according to data provided in 3 to examine the same physical quantities as RBCC engine analysis, according to the same trans-atmospheric trajectory, working in airbreathing mode from sea level steady conditions up to Mach 5. Final acceleration is provided in both cases by pure rocket working mode of engines, allowing to reach the target velocity for orbit insertion. Eventually, mass ratios are computed with Tsiolkovsky equation for each engine, and results of numerical simulations are compared with a hypothetical rocket launcher, based on properties of the space shuttle main engine, to demonstrate the unsatisfactory behavior of a non-airbreathing SSTO vehicle. Simulations results illustrate that despite its complexity SABRE engine is the most suitable solution to develop a SSTO launch vehicle, because of its high thrust and high specific impulse during the entire airbreathing propulsive phase. The design of single stage to orbit launch systems, using combined cycle engines that work both in airbreathing and pure rocket modes, is discussed in this paper analysing the characteristics of the different solutions proposed for the SSTO project. Precooled hybrid airbreathing rocket engines precool the airstream and use a high pressure rocket combustion chamber for both airbreathing and rocket operating modes. This solution allows mass saving and installation simplifications, supporting the potential of the airbreathing mode advantages.