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Numerical Solutions of Transonic to Supersonic Flow over Backward-Forward Facing Step with Heat Flux Conditions
(2026-03-06)
Jeatrakul, Karn
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Prapamonthon, Prasert
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Tanpradit, Ditthaphat
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Wongsatanawarid, Atikorn
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Hao, Zhanzhou
Flows phenomena over a backward-facing step (BFS) and a forward-facing step (FFS) are critical for understanding flow physics in engine, aerodynamic, heat transfer systems. Given the rapid advancement of high-speed technology, the presence of shock waves and aerodynamic heat can have an impact on flow physics, thereby emphasizing the importance of high-speed flow over BFS and FFS with heat transfer. This paper presents numerical solutions of steady two-dimensional viscous turbulent flow over a continuous backward-forward facing step (BFFS) in the transonic to supersonic regime with heat flux conditions using STAR-CCM+. The compressible air and k-ϵ turbulence model are used for the simulations. The effects of inlet Mach numbers ranging from 0.8 to 3.0 and bottom step heat fluxes varying from 0.5 to 10.0 kW/m2 on flow physics are investigated. Numerical results depict flow phenomena such as flow separation, recirculation, and shock wave, as well as thermal distribution. Furthermore, the results show that variations in the inlet Mach number affect flow behaviors, while higher heat fluxes cause dramatical changes in Nusselt number, especially, in the BFS corner for transonic flow.
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Numerical Solutions of Heat Convection Problems in Film Cooling Flow Over Adiabatic and Diabatic Flat Plates
(2026-03-06)
Jeatrakul, Karn
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Prapamonthon, Prasert
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Wongsatanawarid, Atikorn
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Wang, Yeteng
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Hao, Zhanzhou
This paper presents numerical solutions for film cooling flow over a flat plate subjected to heat convection problems, namely (1) adiabatic, and (2) diabatic plates with constant heat fluxes of 500 and 1000 W/m2. The governing equations and realizable k-ε turbulence model are solved to provide numerical solutions in terms of film effectiveness for the adiabatic case, and dimensionless temperature and Nusselt number for the diabatic case. Numerical solutions are carried out at two film hole angles i.e. α = 25° and 35° and two blowing ratios i.e. BR = 0.3 and 0.6. The numerical solutions indicate that the smaller angle and lower blowing ratio can provide better effective cooling on the flat plate for both problem conditions. In addition, the strong influence of the blowing ratio on the film cooling flow is observed. When the heat flux is included, the Nusselt number increases in spanwise and streamwise direction with the heat flux.
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Numerical analysis of airside heat and mass transfer characteristics of fin-and-tube heat exchanger under dehumidifying conditions using VOF method
(2026-01-07)
Boonsuk, Krittawit
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Wongsatanawarid, Atikorn
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Ke, Zhaoqing
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Prapamonthon, Prasert
This paper presents a numerical study of the air-side heat and mass transfer characteristics of a single-row plain fin-and-tube heat exchanger with specific geometrical details under dehumidifying conditions using the volume of fluid (VOF) method with species transport. Moist air, a combination of dry air and water vapor, is used as a working fluid. The Lee model, which is embedded in ANSYS Fluent, is used to implement the phase change model. Without additional source terms defined by user-defined functions, the default value is replaced with mass transfer time relaxation for condensation based on the density of the water liquid phase, the water vapor phase, and mass transfer time relaxation for evaporation. The effects of relative humidity and frontal velocity on heat and mass transfer are presented and discussed. The numerical results in terms of heat and mass transfer-based Colburn factors are validated against those found in the open literatures. The findings indicate that the effect of inlet relative humidity to temperature distribution, flow field and distribution pattern of water vapor mass fraction is small. The air-side heat and mass transfer coefficient are higher while the frontal velocity and inlet relative humidity are higher. The inlet relative humidity has little influence on air-side heat and mass performance when the frontal velocity is low.
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Effects of commercial fin patterns to air-side performance of outdoor air unit (OAU) for operating room during dehumidification in tropical region
(2026-01-07)
Boonsuk, Krittawit
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Wongsatanawarid, Atikorn
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Prapamonthon, Prasert
The design of the outdoor air unit (OAU) for the operating room is always challenging in tropical countries where they should be operated in a wide range of humidity. In this study, the design of the cooling coil for the outdoor air unit has performed with its performance to satisfy the national and international guidelines. The geometrical details of each component and the air-side performance of the OAU main cooling coil are obtained from calculation results performed in commercial software and then validated with experimental results. The validation results show that they are in good agreement for total cooling capacity and sensible cooling capacity within the bound of error of ±7.5% and ±10.0% respectively. Therefore, the condensation rate data validation results show a wider band of error of ±15.0% to cover all experimental results especially for the condensation rate higher that 6 kg/hr. The effects of five different fin patterns on the air-side performance of the OAU main cooling coil are investigated. Based on the determined conditions, the pyramid fin pattern provides the highest total cooling capacity with slightly higher than the corrugated fin. Louvred fin pattern performs the highest sensible cooling capacity and the highest sensible heat ratio among five fin patterns, and pyramids give the lowest. For the condensation rate, the pyramid fin pattern demonstrates the highest value among the rest but slightly higher than the smooth fin. The obtained result from this study is interesting that the pyramid fin pattern demonstrates the highest performance in dehumidifying application.
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Numerical investigation of the impact of wall boundaries on aerodynamic noise in high-speed trains
(2026-01-01)
Ma, Zhi Yuan
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Feng, Qing Song
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Prapamonthon, Prasert
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Cheng, Gong
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Sun, Zhen Xu
As the operating speed of high-speed trains continues to rise, aerodynamic noise has become a critical factor influencing train performance and passenger comfort, especially in confined environments like tunnels. In this study, a comprehensive simulation of the aerodynamic noise generated during the entire ‘open air-tunnel-open air’ transition at 450 km/h was performed using the improved delayed detached eddy simulation (IDDES) turbulence model and overset grid method, with results validated against field measurements. The findings reveal that, compared to open-air conditions, the tunnel environment induces higher-flow velocities around the train, stronger pressure fluctuations on the train surface, and more pronounced vortex shedding in the wake. Sound pressure levels (SPLs) at surface measurement points are typically about 10 dB(A) higher in the tunnel, with the primary differences observed in the 100–300 Hz frequency range, while both scenarios exhibit spectral peaks near 530 Hz. In the bogie region, tunnel noise is dominated by pressure-wave coupling and wall reflections, which amplify low- and mid-frequency components, whereas under open-air conditions, local vortex shedding and wake instabilities prevail, resulting in more high-frequency noise. The web structure contributes to the reduction of aerodynamic noise from the bogie area, with a particularly significant decrease observed in tunnel conditions. Along the tunnel wall, the SPL initially increases and then decreases, reaching a peak of 125.7 dB(A). After exiting the tunnel, the measurement points at Section L in the open air show a reduction of approximately 10 dB(A) compared to the corresponding tunnel-wall points. This study highlights the substantial amplification of low-frequency noise caused by wall confinement and demonstrates the noise-reduction potential of the web structure. The results provide valuable theoretical insights and numerical evidence for aerodynamic noise control in higher-speed train tunnels, offering significant engineering implications.
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Numerical investigation of the aerodynamic noise mechanism in high-speed trains operating at 400 km/h
(2025-08-01)
Huang, Junhui
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Lu, Weishuang
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Sun, Zhenxu
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Prapamonthon, Prasert
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Guo, Dilong
In this study, an improved delayed detached eddy simulation in conjunction with the Ffowcs Williams-Hawkings acoustic analogy is used to numerically compare the aerodynamic noise characteristics of the CR400BF and CR450 high-speed trains operating at 350 and 400 km/h, respectively. The results show that although there are noticeable changes in the distribution of acoustic energy, increasing the operating speed to 400 km/h has no discernible effect on the locations of the main noise sources. The airflow characteristics are optimized by using streamlined front designs, bogie web plates, and fully enclosed skirts, resulting in reduced turbulent kinetic energy and pressure fluctuations. As a result, the noise amplitude in the front car region is effectively reduced, while the formation of small-scale vortices, which can cause noise at high frequencies, is inhibited. However, because of the smoothing of the underbody and the lack of bogie web plates in the middle sections, higher airflow velocities are introduced, intensifying the interaction with the third and fourth bogies. This leads to the increase in noise amplitudes in these regions.
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NUMERICAL ANALYSIS OF FILM COOLING FLOW OVER FLAT PLATE WITH CONVECTIVE HEAT TRANSFER CONDITIONS
(2025-01-01)
Jeatrakul, Karn
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Koysomboon, Annop
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Prapamonthon, Prasert
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Rattanakijsuntorn, Komsan
Film cooling is a systematically designed and widely used technique in cutting-edge gas turbine engines to reduce the surface temperature of gas turbine blades and endwalls, thereby lowering material temperature. Cooling air is emitted from the film holes to protect the external surface, which is exposed to high temperatures from the mainstream gas. As a result, the flow physics of cooling air mixing with the mainstream is critical, and it remains difficult for gas turbine designers to improve cooling efficacy due to the complexity of heat convection phenomena. This paper presents a numerical study onto problems of convective heat transfer in film cooling flow over a flat plate model using 3D computational fluid dynamics (CFD) available in STAR CCM+. The SST k- turbulence model and the realizable k- turbulence model with two-layer all y+ wall treatment are taken into consideration. To solve the problems, the flat plate surface is subjected to adiabatic (Cases 1-2) and constant heat flux conditions of 500 and 1000 W/m2 (Cases 3-6, respectively). The study is conducted at the density ratio (DR) of 1.2 and blowing ratios (BRs) of 0.3 and 0.6. Numerical solutions for both conditions are presented in terms of adiabatic film effectiveness (ηad), dimensionless temperature (θ), and Nusselt number (Nu). Based on a comparative analysis of adiabatic and heat flux conditions, the results show that both the centerline and laterally adiabatic film effectiveness at the two BRs decrease streamwise. At the same BR, the dimensionless temperature values are lower at 1000 W/m2 than at 500 W/m2. This includes less film coverage in the downstream. At BR = 0.6, increasing heat flux from 500 W/m2 to 1000 W/m2 significantly reduces film coverage size in both streamwise and spanwise directions.
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NUMERICAL INVESTIGATION ON DAMAGE SCENARIOS OF VANE TRAILING EDGE USING THERMO-FLUID-STRUCTURAL ANALYSIS
(2025-01-01)
Jeatrakul, Karn
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Tanpradit, Ditthaphat
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Prapamonthon, Prasert
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Raja, Vijayanandh
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Ke, Zhaoqing
Gas-turbine nozzle vanes are used to increase the velocity magnitude of hot gas exiting the combustor. Thus, the vanes must operate at high turbine inlet temperatures (TITs). Essentially, the higher the turbine inlet temperature, the greater the thermal efficiency and propulsive efficiency. Nonetheless, this situation can cause severe damage to the vane material because of the repeated high thermal loads. Using thermo-mechanical analysis, this paper presents damage scenarios of a nozzle vane's trailing edge (TE) and their impact on flow and heat phenomena, including mechanical behavior of the vane material. As the upstream process, computational fluid dynamics (CFD) simulation with conjugate heat transfer (CHT) is used to numerically investigate flow physics and heat transfer phenomena. Then, for the downstream calculations, a static structure model for a steady temperature analysis is used. The NASA-MARK II vane profile is used to define vane boundaries in the computational domain. Broken vane TE scenarios are presented in both the streamwise and spanwise directions, with a short, shallow cutback expanding into a long, deep one from 0.1 cm x 1 cm to 0.3 cm x 3 cm. The numerical results are mainly presented and discussed in terms of variations in surface and internal temperatures, as well as von Mises equivalent stress and strain. The damaged TE, according to the findings, has a significant impact on the thermo-mechanical variations of the vane material. This emphasizes the severity of a damaged vane TE if the turbine is still operating without maintenance.
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A web-based semi-empirical numerical tool for accessible liquid swirl injector design
(2025-01-01)
Uhthalye, Thitut
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Prapamonthon, Prasert
Swirl injectors are vital components to liquid rocket engine combustion intensification, offering high-performance propellant atomisation with relative ease of manufacture. However, despite their widespread use and utility, comprehensive, publicly available practical design methodologies remain scarce in the literature. To address this gap, this paper presents a web-based JavaScript tool employing an iterative semi-empirical numerical method for rapid first-order approximation design of general tangential inlet-type monopropellant and bipropellant liquid swirl injector geometries, based chiefly on the approach described by Bazarov et al. (2004). The tool calculates key geometric and flow parameters—including nozzle radius, radial inlet positions, spray cone angle, and Reynolds numbers—based on user-specified operating conditions such as pressure drop, fluid properties, and geometric coefficients. Special emphasis is given to the efficient implementation of the algorithm for rapid iteration. A computational fluid dynamics validation comparing the computed values against expected flow characteristics is ongoing, with initial results showing promising agreement in limited test cases. Analyses quantifying variances and defining valid regimes of sensible results are in-progress. Additionally, a structured design workflow is also proposed, addressing key limitations such as model prediction deviation due to insufficient air core formation in small injectors. This accessible computation tool aims to assist engineers and students in the predictable and iterative development of swirl injectors.
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Nucleate boiling enhancement on a pillar structure surface with selected surface vibration modes
(2024-08-01)
Ke, Zhaoqing
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Mo, Zhenguo
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Zhang, Chaohua
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Prapamonthon, Prasert
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Zhang, Ying
Pillar structure surfaces and surface vibrations are considered to be two individual techniques to enhance nucleate boiling. In this work, a volume of fluid (VOF) based numerical model is developed to study bubble growth promotion during nucleate pool boiling on a pillar structure surface under the aid of surface vibration. Three vibration modes of the pillar structure, including the horizontal vibration mode (HVM), vertical vibration mode (VVM) and angular vibration mode (AVM), are considered, and their effects on the bubble dynamics and heat transfer are discussed with various vibration amplitudes and frequencies. It is found that the pillar structure surface is favorable for bubble detachment as it constrains the bubble base radius and forces the bubble to grow more vertically compared to the plain surface. Although the HVM and AVM exert no or less vertical force component on the bubble for its detachment than the VVM does, but their horizontal force component significantly alters the bubble shape profile, breaks the force balance, and greatly increases the bubble departure frequency and heat transfer. The largest increment of liquid-vapor phase change rate is found to be 30.9% for the HVM. The bubble departure frequency and the vapor volume flux quantity increase with the pillar vibration amplitude and frequency. This work will deepen our understanding of fundamental bubble growth mechanisms as altered by vibration on the pillar structure surface for better heat transfer applications.

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