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This study experimentally investigates the effects of nose-tip bluntness on boundary-layer transition over a 7 ∘ half-angle cone at Mach 6.76, using the Seoul National University Hypersonic Shock Tunnel. Transition characteristics were examined through high-speed schlieren visualization, surface heat flux measurements, and high-frequency surface pressure measurements for varying nose-tip radii (0.1 mm, 1 mm, and 2 mm) and unit Reynolds numbers. Increasing nose-tip bluntness effectively delayed transition onset, as indicated by turbulent intermittency and heat flux distributions. Spectral proper orthogonal decomposition and pressure spectral analyses revealed distinct second-mode instabilities with frequency shifts to lower values as bluntness increased. Additionally, a low-frequency instability around 200 kHz was identified in the configuration with a 2 mm nose-tip radius, suggesting the presence of multiple instability modes. These observations highlight the influence of nose-tip bluntness on hypersonic boundary-layer stability and emphasize the necessity for comprehensive consideration of multiple instability modes in hypersonic vehicle design.

This numerical study was conducted to investigate the flow properties in a model scramjet configuration of the experiment in the T4 shock tunnel. In most numerical simulations of flows in shock tunnels, the inflow conditions in the test section are determined by assuming the thermal equilibrium of the gas. To define the inflow conditions in the test section, the numerical simulation of the nozzle flow with the given nozzle reservoir conditions from the experiment is conducted by a thermochemical nonequilibrium computational fluid dynamics (CFD) solver. Both two-dimensional (2D) and three-dimensional (3D) numerical simulations of the flow in a model scramjet were conducted without fuel injection. Simulations were performed for two types of inflow conditions: one for thermochemical nonequilibrium states obtained from the present nozzle simulation and the other for the data available using the thermal equilibrium and chemical nonequilibrium assumptions. The four results demonstrate the significance of the modelling approach for choosing between 2D or 3D, and thermal equilibrium or nonequilibrium.

Coughing and sneezing are the main ways of spreading coronavirus-2019 (SARS-CoV-2). People sometimes need to work together at close distances. This study presents the results of the computational fluid dynamics (CFD) simulation of the dispersion and transport of respiratory droplets emitted by an infected person who coughs in an indoor space with an air ventilation system. The resulting information is expected to help in risk assessment and development of mitigation measures to prevent the infection spread. The turbulent flow of air in the indoor space is simulated using the k-ε model. The particle equation of motion included the drag, the Saffman lift, the Brownian force and gravity/buoyancy forces. The innovation of this study includes A: Using the Eulerian–Lagrangian CFD model for the simulation of the cough droplet dispersion. B: Assessing the infection risk by the Wells–Riley equation. C: A safer design for the ventilation system (changing the ventilation supplies and exhausts in the indoor space and choosing the right location for air ventilation). The droplet distribution in the indoor space is strongly influenced by the air ventilation layout. The air-curtain flow pattern significantly reduces the dispersion and spreading of virus-infected cough droplets. When the ventilation air flow occurs along the room length, it takes about 115 s for the cough droplets to leave the space. However, when the ventilation air flow is across the width of the indoor space and there are air curtain-type air flow patterns in the room, it takes about 75 s for the cough droplets to leave the space.

A large eddy simulation (LES) and combustion instability analysis are performed using OpenFOAM for the multiple shear-coaxial injector combustor DLR-BKD (in German Deutsches Zentrum für Luft–Brennkammer D, German Aerospace Center–Combustion Chamber D), which is a laboratory-scale combustor operating in a real-gas environment. The Redlich–Kwong–Peng–Robinson equation of state and steady-laminar flamelet model are adopted in the simulation to accurately capture the real-gas combustion effects. Moreover, the stable combustion under the LP4 condition is numerically analyzed, and the characteristics of the combustion flow field are investigated. In the numerical simulation of the combustion instability, the instability is generated by artificially superimposing the 1st transverse standing wave solution on the stable combustion solution. To decompose the combustion instability mode, the dynamic mode decomposition method is applied. Several combustion instability modes are qualitatively and quantitatively identified through contour plots and graphs, and the sustenance process of the limit cycle is investigated.

A large-eddy simulation (LES) of a gaseous hydrogen/liquid oxygen (GH2/LOX) single-injector rocket combustor is performed in this study. The Redlich–Kwong–Peng–Robinson (RK–PR) equation of state is used to simulate the real-gas effect under high-pressure conditions, and the steady laminar flamelet model (SLFM) is implemented to simulate fast chemistry, such as a H2/O2 reaction. From the numerical simulation, the characteristics of time-averaged flow and flame fields are obtained, and their relationship with the real-gas effect is investigated. It is possible to investigate unsteady flame features and the mixing mechanism of propellants in detail by examining multiple snapshots of the field contour. Another purpose of the study is to investigate the differences in flow and flame structures according to the variation in the turbulent Schmidt number. By comparing the simulation result with the natural OH* emission image and temperature profiles from experimental data, the appropriate range of the turbulent Schmidt number for the simulation is obtained. Furthermore, this paper suggests the usefulness and validity of the current research by quantitatively comparing (i.e., temperature profiles) numerical results with those of existing literature.

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

The objective of this study is to enhance the methodology for the design of a supersonic wind tunnel, improving the process with advanced computational techniques. The supersonic wind tunnel is intended to operate within a flight envelope of Mach 2.5 to 4 and altitudes between 18 and 20 km; this study focuses on the operative condition of Mach 3.5. The research is based on computational fluid dynamics, enabling a deeper understanding of fluid flow phenomena that can deteriorate the operability of the wind tunnel. Additionally, a detailed mesh independence study has been conducted to ensure the reliability and robustness of the computational results. These new analyses allowed for a more comprehensive optimization in the state of the art of tunnel geometry and operational conditions, further enhancing the ability to sustain supersonic flow for extended durations. Particular attention was given to the second throat, which plays a crucial role in the overall performance of the facility, especially during the start-up process. Its design has been refined to improve efficiency by reducing the minimum starting pressure.

Ramjet or scramjet engines, high-speed air-breathing propulsion systems, can only be operated in supersonic and hypersonic regions. Therefore, ramjet or scramjet engines are not used alone but in the form of a combined cycle, such as the turbine-based combined cycle (TBCC) and rocket-based combined cycle combined with turbine or rocket engines. Configuration design of the variable inlet is necessary because operation in a wide range of Mach numbers is essential in these integrated propulsion systems. This study presented a detailed design procedure for a 2D variable inlet for TBCC engines, taking into account the changing mass flow rate conditions based on mission trajectories. The design procedure was validated by deriving the mass flow requirements for the aircraft conceptually and designing the variable inlet geometry accordingly. The designed variable inlet geometry underwent boundary layer correction, accounting for viscous effects. Subsequently, the performance of the designed variable inlet was analyzed through numerical simulations. A comparison of the outlet performance with inlets operating in a similar range and design conditions confirmed the significant improvement achieved by the designed variable inlet.

This paper presents the operational capabilities and the characteristics of the nozzle flow of the Seoul National University Hypersonic Shock Tunnel (SHyST), a recently added impulse facility designed to produce high-enthalpy flows reaching up to 5 MJ/kg through hypersonic contoured nozzles. Within this investigation, emphasis is placed on the design and utilization of a pitot rake, serving as an essential instrument for quantifying pitot pressure and Mach number distributions throughout the test section. The experimental results confirm the presence of axis-symmetric behavior and spatial–temporal uniformity of the freestream Mach number at the nozzle outlet and along the test section. In addition, the study demonstrates a good agreement with the predictions of numerical simulation. Mach number validation is further supported by the measurement of shock standoff distance through schlieren visualization.

Space exploration presents environmental challenges, including microgravity, high-energy radiation, and extreme temperature changes. Accelerated aging in space provides a unique opportunity to study age-related neurodegenerative diseases. Tauopathies, such as Alzheimer's disease, are characterized by neurofibrillary tangles of hyperphosphorylated tau protein in the brain. We studied how time-averaged simulated microgravity (taSMG), which replicates space conditions, affects tauR406W-induced neurotoxicity in transgenic flies. Applying taSMG at an early stage of neurodegeneration reduced severe locomotion impairment in tauR406W-expressing flies. This protective effect was sustained, specific to the tau mutation, and dependent on the timing, duration, and severity of tau expression. Transcriptomic analysis revealed that taSMG normalizes gene expression related to the extracellular environment, innate immune response, and olfactory function. These results underscore gravity's role in modulating tauopathy and suggest that microgravity may potentially offer new therapeutic insights for neurodegenerative diseases.