Search Results (62)

In this study, the nonlinear forced vibration response of fiber-reinforced laminated composite beams coated with functionally graded materials (FGMs) is investigated under the combined action of aero-thermoelastic loads and a concentrated harmonic excitation. The mathematical formulation is established using the Euler–Bernoulli beam theory, where von Kármán geometric nonlinearities are taken into account, along with the modified third-order piston theory to represent aerodynamic effects. By neglecting axial inertia, the resulting set of nonlinear governing equations is simplified into a single equation. This equation is discretized through the Galerkin procedure, yielding a nonlinear ordinary differential equation. An analytical solution is, then, obtained by applying the method of multiple time scales (MTS). Furthermore, a comprehensive parametric analysis is carried out to evaluate how factors such as the power-law index, stacking sequence, temperature field, load amplitude and position, free-stream velocity, and Mach number influence both the lateral dynamic deflection and the frequency response characteristics (FRCs) of the beams, offering useful guidelines for structural design optimization. Full article

The growing demand for micro-launchers capable of placing payloads between 1 and 100 kg into low Earth orbit stems from rapid advances in electronics and the resulting increase in nanosatellite capabilities. Simultaneously, space programs are prioritizing the use of alternative propellants, those that are more sustainable, cost-effective, and readily available. As a result, modern launcher development emphasizes versatility, reliability, reusability, and adaptability to various working fluids. This paper presents the experimental validation of a supersonic turbine design methodology tailored for such adaptable systems. The focus is on a turbine class intended for a turbopump in micro-launchers with payload capacities around 100 kg. The experimental campaign employed two working fluids (air and methane) to assess the method’s robustness. The validation was performed on a stator only planar model, and the experimental data was compared with the analytical result obtained through the Mach number similarity criterion. The results confirm that the approach accurately identifies flow similarity through Mach number matching, even when the working fluid changes. Comparative analysis between experimental data and predictions demonstrates the method’s reliability, with measurement uncertainties also addressed. These findings support the methodology’s applicability in practical engine design and adaptation. Future work will explore enhancements to improve predictive capability and flexibility. The method may be extended to other systems where fluid substitution offers design or operational advantages. Full article

Fuel injection and mixing remain a critical challenge in the development of supersonic propulsion systems. The efficiency of both mixing and combustion significantly influences the overall performance of these systems, underscoring the importance of optimizing fuel injection strategies. Injector arrays are extensively employed in such propulsion systems; however, conventional design methodologies predominantly focus on global mixing efficiency, neglecting injector-specific performance metrics. This research introduces a fuel trajectory tracing methodology, wherein hydrogen from each injector is treated as a distinct species, despite having identical physical and chemical properties. This approach enables the tracking of hydrogen transport and mixing within supersonic flows. The methodology has been demonstrated to accurately capture the mass fraction distribution of hydrogen from individual injectors without perturbing the flow field. Based on these distributions, injector-specific mixing and combustion efficiencies can be quantified, providing valuable insights for optimizing injector configurations and enhancing propulsion system performance. Full article

Scramjet operation requires a comprehensive understanding of the internal flowfield, encompassing fuel–air mixing and combustion. This study investigates transient flow and flame development within a HIFiRE-2 scramjet engine combustor, which features two opposing cavities and dual sets of fuel injectors—the upstream (primary) and downstream (secondary) injectors. These cavities function as flameholders, creating circulating flows with elevated temperatures and pressures. Shock waves form both ahead of fuel plumes and at the diverging and converging sections of the flowpath. Special attention is given to the interactions among these shock waves and the shear layers along the supersonic core flow as the system progresses towards a quasi-steady state. Driven by increased backpressure, bow shocks and disturbances induced by the normal, secondary fuel injection and the inclined, primary fuel injection move upstream, amplifying the cavity pressure. These shocks generate adverse pressure gradients, causing near-wall flow separation adjacent to both injector sets, which enhances the penetration and dispersion of fuel plumes. Once a quasi-steady state is achieved, a feedback loop is established between dynamic wave motions and combustion processes, resulting in sustained entrainment of reactive mixtures into the cavities. This mechanism facilitates stable combustion in the cavities and near-wall separation zones. Full article

This work analyzes the aero-elastic oscillations of cantilever beams reinforced by carbon nanotubes (CNTs). Four different distributions of single-walled CNTs are assumed as the reinforcing phase, in the thickness direction of the polymeric matrix. A modified third-order piston theory is used as an accurate tool to model the supersonic air flow, rather than a first-order piston theory. The nonlinear dynamic equation governing the problem accounts for Von Kármán-type nonlinearities, and it is derived from Hamilton’s principle. Then, the Galerkin decomposition technique is adopted to discretize the nonlinear partial differential equation into a nonlinear ordinary differential equation. This is solved analytically according to a multiple time scale method. A comprehensive parametric analysis was conducted to assess the influence of CNT volume fraction, beam slenderness, Mach number, and thickness ratio on the fundamental frequency and lateral dynamic deflection. Results indicate that FG-X reinforcement yields the highest frequency response and lateral deflection, followed by UD and FG-A patterns, whereas FG-O consistently exhibits the lowest performance metrics. An increase in CNT volume fraction and a reduction in slenderness ratio enhance the system’s stiffness and frequency response up to a critical threshold, beyond which a damped beating phenomenon emerges. Moreover, higher Mach numbers and greater thickness ratios significantly amplify both frequency response and lateral deflections, although damping rates tend to decrease. These findings provide valuable insights into the optimization of CNTR composite structures for advanced aeroelastic applications under supersonic conditions, as useful for many engineering applications. Full article

Three-dimensional (3D) computational fluid dynamic (CFD) simulations have been performed to investigate the complex flow features and stripping of fluid materials from a cylindrical water drop at the late-stage in a Shock Liquid Drop Interaction (SLDI) process when the drop’s downstream end experiences compression after it is impacted by a supersonic shock wave ($Ma$ = 1.47). The drop trajectory/breakup has been simulated using a Lagrangian model and the unsteady Reynolds-averaged Navier–Stokes (URANS) approach has been employed for simulating the ambient airflow. The Kelvin–Helmholtz Rayleigh–Taylor (KHRT) breakup model has been used to capture the liquid drop fragmentation process and a coupled level-set volume of fluid (CLSVOF) method has been applied to investigate the topological transformations at the air/water interface. The predicted changes of the drop length/width/area with time have been compared against experimental measurements, and a very good agreement has been obtained. The complex flow features and the qualitative characteristics of the material stripping process in the compression phase, as well as disintegration and flattening of the drop are analyzed via comprehensive flow visualization. Characteristics of the drop distortion and fragmentation in the stripping breakup mode, and the development of turbulence at the later stage of the shock drop interaction process are also examined. Finally, this study investigated the effect of increasing $Ma$ on the breakup of a water drop by shear stripping. The results show that the shed fluid materials and micro-drops are spread over a narrower distribution as $Ma$ increases. It illustrates that the flattened area bounded by the downstream separation points experienced less compression, and the liquid sheet suffered a slower growth. Full article

This study investigates the aerodynamic performance of a fourth-generation normal shockwave inlet system, with a primary focus on minimizing pressure losses and ensuring uniform airflow distribution. A computational model was developed, incorporating a section of the fuselage along with the complete inlet duct. The model was discretized using a hybrid mesh approach to enhance numerical accuracy. The analysis was conducted at a flight altitude of 8000 m, encompassing 370 distinct cases defined by varying angles of attack and Mach numbers. This comprehensive parametric study yielded a dataset of 10,800 total pressure measurements across predefined sampling locations. Based on the obtained results, flow distortion coefficients in both circumferential (CDI) and radial directions (RDI) were systematically determined for each test case. The interdependencies between CDI, RDI, Mach number, and angle of attack (α) were analyzed and presented in a consolidated manner. In the second phase of the study, an artificial neural network (ANN) utilizing a Feed-Forward architecture was implemented to predict pressure distributions for intermediate flight conditions. The ANN was trained using the CFG algorithm, and the predictive accuracy was assessed through the determination coefficients computed by comparing ANN-based estimates with numerical simulation results. The findings demonstrate the efficacy of ANN-based modeling in enhancing the predictive capabilities of inlet flow dynamics, offering valuable insights for optimizing next-generation supersonic air intake systems. Full article

This study numerically explores the feasibility of a streamlined heat pipe heat exchanger in precooling technology in supersonic vehicles. Emphasis has been placed on the role of fins installed in the condensation section in affecting the aerodynamic and thermal characteristics of the streamline heat pipe heat exchanger. The results show that the installation of fins in the condensation section effectively improved the overall heat transfer capacity of the streamline heat pipe heat exchanger. The temperature drop with fins is up to 685 K, which is 20 K larger than the case without fins. Simultaneously, fins resulted in 6.4% and 25.4% increases in the pressure loss coefficient in the evaporation and condensation section compared to the case without fins. The aerodynamic and thermal characteristics are closely related to the mass flow rate of intake air and kerosene (RP-3). The pressure drop and temperature drop are positively related to the mass flow rate of RP-3. In contrast, as the q_a increases, the heat exchange per q_a decreases, and the temperature of the air outlet of the evaporation section increases correspondingly. In the evaporation section, as the q_RP-3 increases, the temperature drop in the condensation section first increases and then remains unchanged, and its pressure loss coefficient decreases. The temperature drop in the intake air is positive and related to the q_RP-3. The results obtained in this study are significant because they can provide technical support in the high performance of heat exchangers. Full article

Supersonic vacuum generators, or ejectors, operate pneumatically to extract air from tanks in industrial applications. A key performance metric for ejectors is the Total Evacuation Time (TET), which measures the time required to reach minimum pressure. This research predicts TET using empirical models that rely on two key metrics: the characteristic curve, which relates absorbed flow rate to the working pressure, and the polytropic curve, which describes the evolution of the polytropic coefficient across working pressures. Accurately capturing both curves for subsequent fitting to polynomial curves is crucial for forecasting TET. Several experimental setups were employed to capture the curves, each of which refined the data and improved the quality of the polynomial fits and coefficients. Multiple setups were necessary to pinpoint the breakpoint, from supersonic to subsonic operation mode, which is a critical factor that affects the characteristic curve and the TET. Furthermore, the research shows an improvement in the TET forecasts for each setup, with deviations between experimental and predicted TET ranging from 7.6% (14.5 s) to a 1.4% (2.6 s) in the most precise setup. Once the models were validated, an optimized ejector design, extracted from an author’s previous article, was tested. It revealed a 4% improvement (8 s) in the TET. These results highlight the importance of the mathematical models developed, which can be used in the future to compare ejectors and reduce the need for experimental data. Full article

Numerical investigations were conducted to analyze the coupling effects of pulsed H₂ jets and nanosecond-pulsed actuation (NS-SDBD) in a supersonic crossflow. The FVM was employed to solve the multi-component 2D URANS equations with the SST k-omega turbulence model, while H₂-air combustion was described using a seven species–seven reactions chain reaction model, and the plasma thermal effect was represented by a phenomenological model. The backward-facing step flows with an inlet Mach number of 2.5 and a pulsed jet frequency of 10 kHz under different actuation conditions were simulated. The combustion enhancement mechanism under an actuation frequency of 20 kHz was analyzed. Research indicates that compression waves induced by NS-SDBD enhance H₂-air mixing and facilitate temperature transport as the flow progresses. This progress is significantly associated with the flow structures generated by pulsed jets. Under this condition, the fuel utilization rate in the flow field increased by 61.2%, the total pressure recovery coefficient increased by 5.34%, and the outlet total temperature slightly increased even with a 50% reduction in fuel flow rate. Comparative analysis of different actuation cases demonstrates that evenly distributed actuation within the jet cycle yields better effects. The innovation of this study lies in proposing and exploring a potential method to address inadequate combustion under high-speed inflow conditions, which couples NS-SDBD with pulsed hydrogen jets. Full article

In a supersonic state, the aero-engine operates under harsh circumstances of elevated temperature, high pressure, and rapid rotor speed. This work provides an innovative high-stability control technique for engines with fixed-geometry inlets, addressing stability control issues at the aero-propulsion system level. The discussion begins with the importance of an integrated model for the intake and the aero-engine, introducing two stability indices (surge margin and buzz margin) to characterize inlet stability. A novel predictive model for engine air mass flow is developed to address the indeterminate issue of engine air mass flow. The integration of input parameters in the predictive model is refined using the least squares support vector regression (LSSVR) algorithm, and historical input data is used to enhance predictive performance, as validated by numerical simulation results. A data-driven adaptive augmented linear quadratic regulator (d-ALQR) control technique is suggested to adaptively modify the control parameters of the augmented linear quadratic regulator. A highly stable control strategy is finally proposed, integrating the predictive model with the d-ALQR controller. The simulation results conducted during maneuvering flight operations demonstrate that the developed high-stability controller can maintain the inlet in an efficient and safe condition, ensuring optimal compatibility between the engine and the inlet. Full article

In order to reduce the infrared radiation intensity of supersonic tail nozzles and in response to the increasingly severe battlefield infrared environment, simulations were conducted on axisymmetric expanding tail nozzles to study the effects of air, liquid nitrogen, and dry ice cold flows at different flow rates on the nozzle wall temperature. The results show that when the dry ice flow rate is increased by 1 kg/s, the maximum temperature of the wall surface in the expansion section decreases by about 40 K. At a cold flow rate of 5% in the 0° detection direction, the intensity of infrared radiation was reduced by 20.8% for the liquid nitrogen cold flow and 26.3% for the dry ice cold flow, compared to the cold flow of injected air. The IR suppression of the tail nozzle was significant in the range from α = 0 to 50°. Compared to cooling air, the maximum IR radiation intensity was reduced by 26.5% for dry ice and 20.4% for liquid nitrogen. When the flow rate of the injected cold stream was increased by 4%, the intensity of the infrared radiation from the nozzle was reduced by 52.6%, 55.8%, and 66.2% for the injected air, liquid nitrogen, and dry ice cold streams, respectively. Full article

Atmospheric air, being also a moist gas, is present as a working medium in various areas of technology, including the areas of airframe aerodynamics and turbomachinery. Issues related to the condensation of water vapor contained in atmospheric air have been intensively studied analytically, experimentally and numerically since the 1950s. An effort is made in this paper to present new, unique and complementary results of the experimental testing of moist air expansion in the de Laval nozzle. The results of the measurements, apart from the static pressure distribution on the nozzle wall and the images obtained using the Schlieren technique, additionally contain information regarding the quantity and quality of the condensate formed due to spontaneous condensation at the transition from the subsonic to the supersonic flow in the nozzle. The liquid phase was identified using the light extinction method (LEM). The experiments were performed for three geometries of convergent–divergent nozzles with different expansion rates of 3000, 2500 and 2000 s⁻¹. It is shown that as the expansion rate increases, the phenomenon of water vapor spontaneous condensation appears closer to the critical cross-section of the nozzle. A study was performed of the impact of the air relative humidity and pollution on the process of condensation of the water vapor contained in the air. As indicated by the results, both these parameters have a significant effect on the flow field and the pressure distribution in the nozzle. The results of the experimental analyses show that in the case of the atmospheric air flow, in addition to the pressure, temperature and velocity, other parameters must also be taken into account as boundary parameters for possible numerical analyses. Omitting information about the air humidity and pollution can lead to incorrect results in numerical simulations of transonic flows of atmospheric air. The presented results of the measurements of the moist air transonic flow field are original and fill the research gap in the field of experimental studies on the phenomenon of water vapor spontaneous condensation. Full article

In this study, the impacts of laser irradiation on the surface morphology and hardness of copper (Cu) are investigated under various environments, including air, vacuum, and high-pressure gas flow through a supersonic nozzle. After irradiating Cu targets with laser pulses with energy of 30, 60, and 90 mJ/pulse, the surface structures of the targets are analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM analysis reveals diverse surface morphologies, including micro-cones, cavities, droplets, ripples, and island-like structures, depending on laser energy and environments. The XRD analysis provides insights into the structural changes induced by laser irradiation. The results indicate a significant enhancement in microhardness by a factor of 2.77, which is attributed to the surface and structural modifications incurred under various environments. In addition, the XRD analysis reveals a shift in the residual stress in the surface layers of copper from tensile before laser irradiation to compressive afterwards, highlighting the effectiveness of laser surface treatment in inducing favorable mechanical properties. Full article

In order to further improve the oxidation resistance of SiC-coated C/C composites used in extreme environments, TaSi₂ coatings were deposited on the surfaces of SiC-coated C/C composites by supersonic air plasma spraying (SAPS) with different spraying power parameters, under other fixed parameter (gas flow, power feed rate, spraying distance and nozzle diameter) conditions. The micro-structures and phase characteristics of the TaSi₂ coatings prepared with the four kinds of spraying powers (40 kW, 45 kW, 50 kW and 55 kW) were analyzed. Also, the inter-facial bonding strengths and fracture modes between the four TaSi₂ coatings and the SiC coating were studied. The results showed that with an increase in the spraying power, the morphologies of the TaSi₂ coatings appeared from loose to dense to loose. When the spraying power was 50 kW, the deposition rate reached a maximum of 39.8%. The TaSi₂ coating presented an excellent micro-structure without obvious pores and microcracks, and its inter-facial bonding strength was 15.3 ± 2.3 N. Meanwhile, the fracture surface of the sample exhibited a brittle characteristic. Full article