The trailing edge of gas turbine blades encounters concentrated heat loads, necessitating cooling techniques distinct from those used in mid-chord regions. Narrow cooling channels in these areas typically incorporate pin fins or dimples for internal cooling. In contrast, external cooling relies on cutback film cooling configurations, which differ significantly from mid-chord designs. Large eddy simulation (LES) has emerged as a powerful tool for investigating heat transfer in these challenging environments, capturing intricate flow phenomena and turbulence effects that Reynolds-Averaged Navier–Stokes (RANS) simulations often cannot resolve. This review synthesizes findings from 54 LES-based studies on trailing edge cooling, focusing on three key configurations: pin fin arrays, dimpled surfaces, and cutback film cooling. LES consistently demonstrated higher accuracy in predicting heat transfer and cooling effectiveness, outperforming RANS by resolving complex flow structures such as horseshoe vortices, shear layer vortices, and unique flow interactions inherent to these geometries. Furthermore, LES provided detailed turbulence statistics and local heat transfer distributions, offering critical insights for optimizing and improving predictive models. Beyond its demonstrated capabilities, this review underscores the future potential of LES in advancing shape optimization, transient flow analysis, and multi-physics simulations, including conjugate heat transfer and flow-structure interactions.

This study explores the optimization of wavy-slit fins in the indoor units of air conditioners that use low-global-warming-potential refrigerants, with a focus on the interactions between slit length, width, and height. A response surface method was employed to analyze the trade-offs between thermal performance and pressure loss, and numerical optimization was performed using two objective functions: pumping power and volume goodness factor (Gv). The results demonstrated that optimizing the slits’ geometry significantly enhanced overall performance. For pumping power, a minimum point was observed near the design boundaries, which underscores the critical role of geometric interactions. The flow and temperature field analysis under fixed heat-duty conditions revealed substantial flow separation caused by the slits, enhanced mixing between the upper and lower surfaces, and a reduction of up to 2.05% in pumping power. In contrast, the Gv optimization model exhibited a more uniform flow, reducing flow separation beyond the pipe and improving the Gv by 1.85%, although it led to an increase in pumping power. These findings highlight the potential that tailored slit fin designs have to achieve a balanced enhancement in heat transfer and aerodynamic performance, offering valuable insights for the development of efficient, low-environmental-impact air conditioning systems.

Advances in computational fluid dynamics (CFD) are essential for understanding the complex behaviors of fluids in various conditions [...]

에어컨 실내기는 핀-관 열교환기로 구성되는데 관군의 공기유동의 불균일도가 냉방 성능에 큰 영향을 미친다. 냉매 공급 회로를 효과적으로 구성하여 이를 해결할 수 있으나 이를 위해서는 각각의 관에 대한 기류 분포에 대한 정보가 필요하다. 본 연구에서는 실내기의 내부 구조를 반영하여 3차원 전산유체 해석을 수행하여 실내기의 각 튜브에서 발생하는 유동 불균일성을 예측하였다. 복잡한 핀 구조는 다공체로 근사하였고 입구 유동은 실험으로 측정한 자료를 경계 조건으로 부과하여 입구 유동의 영향을 파악하였다. 공기 유동은 흡입 팬으로 생성하는데 이를 압력 경계조건과 출구 조건으로 각각 구현하여 경계조건의 영향을 파악하였다. 실내기 튜브에서 발생하는 유동 불균일도에는 입구 유동 분포가 큰 영향을 끼치는 것을 확인하였고 출구 경계조건의 영향은 상대적으로 적은 것으로 나타났다.

Industrial boilers cause significant energy wastage that could be mitigated with oxy-fuel combustion versus traditional air combustion. Despite several feasibility studies on oxy-fuel burners, they are widely avoided in industry due to major infrastructural challenges. This study measured the performance and heat transfer characteristics of each component in a 0.5 MW fire tube gas boiler after retrofitting it with an oxy-fuel burner. Comparisons were drawn across three combustion modes—air combustion, oxy-fuel combustion, and oxy-fuel flue gas recirculation (FGR). The Dittus–Boelter equation was employed to predict heat transfer in the fire tube for all combustion modes at full load (100%). Heat transfer in the latent heat section of the economizer was measured and compared with predictions using the Zukauskas equation. With this retrofit, oxy-fuel combustion improved the thermal efficiency by about 3–4%. In oxy-fuel combustion, the flow rate of exhaust gas decreased. When integrated into an existing fire tube boiler, the fire tube’s heat transfer contribution diminished greatly, suggesting the economic viability of a redesigned, reduced fire tube section. Additionally, a new design could address the notable increase in gas radiation from the fire tube in oxy-fuel and FGR, as well as aid in the efficient recovery of condensation heat from exhaust gases.

In this study, a series of computational fluid dynamics (CFD) simulations was performed on a small -diameter finned tube heat exchanger equipped with wavy -slit fins. Heat transfer and pressure drop characteristics were analyzed according to changes in three geometric variables related to the slit: height, length, and width. As the slit height increased, both j and f factors tended to increase and then decrease. Further, as the slit length increased, both j and f factors also tended to increase and then decrease. In the case of the slit width, both j and f factors increased, but the effect was small compared to other geometric variables. The wavy -slit fins constructed by applying the optimal value of each variable did not provide optimal performance. It was concluded that an optimal design considering the mutual interference of three geometric variables is necessary.

Brush seals are extensively utilized in rotating machinery such as gas turbines, aircraft engines, and compressors owing to their ability to provide effective sealing while accommodating radial, axial, and angular movements between components. In this study, Flomaster, a commercial one-dimensional code, was employed to conduct simulations under conditions with a gap or in which the influence of the fence is considered and compared with existing data. When no gap existed in the brush seal, the one-dimensional code properly predicted the leakage flow rate; however, a significant error occurred when a gap existed. Furthermore, the variation in leakage flow rate according to changes in fence height, an important variable in brush seals, was calculated using the one-dimensional code. While the leakage flow rate predicted by the one-dimensional code agreed well with the results from computational fluid dynamics (CFD), discrepancies were observed compared with experimental data.

: This study aimed to develop a heat recovery system for a 1-MW-class cogeneration system with a gas engine. The system recovers heat from two engine components-jacket - jacket water and exhaust gas. A plate-type heat exchanger captures heat from the jacket water, contributing to room heating and hot water supply. Additionally, the exhaust gas heat is harnessed to generate steam. Both heat recovery devices were subjected to 1/5-scale experiments, and the results were compared against empirical correlations used for designing thermal systems. The thermal efficiency of the plate-type heat exchanger decreased by up to 30% at 50% engine load. Thus, although its heat transfer accuracy varied by up to 50% based on fin density changes, the proposed modular evaporator exhibited good performance.

Brush seals are extensively used in rotating equipment, such as gas turbines and compressors, providing effective sealing while accommodating radial, axial, and angular movements between components. In this study, the performance of brush seals with and without clearances was predicted through axisymmetric 2D computational fluid dynamic (CFD) simulations using a porous media model. Because the accurate modeling of a brush seal requires the appropriate porosity to be determined and the flow resistance to be calculated, a porosity correction was performed based on the brush seal’s geometry and pressure ratio. The corrected porosity was then used to calculate the flow resistance and the leakage flow rate was predicted. Based on the results, the corrected porosity significantly improved the accuracy of the previously unreliable leakage flow rate predictions, regardless of the presence of clearances. For cases with a clearance, the blow-down effect was determined through CFD simulations for the given geometry and was compared with experimental data. The leakage flow rate predictions were highly accurate, with a relative error of less than 5% across a pressure ratio range of 1.5–4.

Herein, 50 articles published over the past 20 years on using large eddy simulation (LES) for the internal cooling passage of a gas turbine, especially the mid-chord ribbed channel, are reviewed for the first time. First, the numerical challenges of performing LES on a ribbed channel and experimental verification are summarized. Next, LES data and the major engineering findings that are difficult to obtain experimentally or using Reynolds-averaged Navier–Stokes simulation (RANS) are covered, and heat transfer on and inside the rib, and the effects of rotation and buoyancy are discussed. Next, recent LES studies related to the shape of the ribbed channel are reviewed, and finally, the contribution of using LES for research on the internal cooling of gas turbines in the future, including those with ribbed channels, is anticipated.

Non-furnace boilers can improve the efficiency of industrial once-through boilers. However, temperature non-uniformity occurs in the economizer connected vertically to the boiler. Heat transfer performance is degraded by temperature non-uniformity. To solve this problem, a corbel was installed on the side wall of the economizer, and a baffle was installed on the transition duct. Consequently, although the thermal efficiency of the boiler was improved, significant temperature non-uniformity was still observed in the area upstream of the economizer. To address this issue, this study designed a turning guide vane (TGV) at the economizer inlet using computational fluid dynamics (CFD). First, CFD was performed for a case without a guide vane and a case with an existing baffle installed. By analyzing the streamlines obtained using CFD, two TGV designs were proposed. In the first design, guide vanes were installed along the desired streamline, and the concept of the existing TGV was followed. In the second design, an attempt was made to minimize the pressure drop by arranging guide vanes at the inlet. Both designs reduced the standard deviation of temperature by more than 30% and improved the volume goodness factor by 25%.

The demand for computational fluid dynamics (CFD)-based numerical techniques is increasing rapidly with the development of the computing power system [...]

The performance of Labyrinth seal for sealing the secondary flow path of a gas turbine was predicted using Flomaster, a 1-dimensional code. First, the predictive ability of the straight-through seal module built into Flomaster was verified by comparing it with experimental data. The discharge coefficient was confirmed through the isentropic mass flow rate and the actual mass flow r ate found in Martin’s equation. The validity of the prediction using the one-dimensional code was verified through the straight-through seal, and the discharge coefficient according to the geometric variables was predicted using the stepped seal module built into the Flomaster. The performance of the seal predicted by the one-dimensional code was verified by comparing the results obtained with the three-dimensional CFD (computational fluid dynamics) data. Among the design variables of the stepped seal, the most important variable is the step height, but the effect is reduced above a certain height, so the design equation of the one-dimensional code could be used.

Film cooling has dramatically contributed to the performance improvement of gas turbines, as it is a very effective cooling technique for gas turbines. Large eddy simulation (LES) began to be used in the study of film cooling 20 years ago, and meaningful results have been found, but it has not yet been intensively reviewed. In this review paper, we analyze and introduce about 70 papers published on LES of film cooling over the past 20 years. Numerical instability must be overcome, and realistic inflow must be generated to perform LES of film cooling. This review summarizes how the groups that performed LES of film cooling solved these problems. In film-cooling research, the main topics are improving the film-cooling performance by preventing the lift-off of the injectant and the effect of flow conditions on film cooling. In addition, LES has also been conducted extensively on the above two topics, and this review focuses on them. Finally, turbulence statistics of film-cooling flow obtained from LES are introduced, and future challenges of film-cooling LES are predicted.

A series of numerical simulations were performed to study the discharge coefficient based on the geometric parameters of a stepped labyrinth seal that sealed the secondary flow path of a gas turbine. In contrast with straight-through seals, stepped labyrinth seals introduce additional geometrical parameters related to the steps. In this study, three shape variables were observed: step height (SH), position, and cavity width (CW). The sensitivity to the leakage flow of the shape variable in the stepped labyrinth seal was analyzed. The mechanism for improving the sealing performance of stepped labyrinth seals was investigated. The results indicated that the stepped labyrinth seal exhibited up to 17.9% higher leakage-suppression performance than the straight labyrinth seal. Seals with large discharge coefficients had a large vena contracta upstream of each tooth structure and a rapidly accelerated axial velocity in the radial direction. We could observe that the discharge coefficient changed according to the flow field in the cavity. The wall shear stress was sensitive to the SH but not to the CW or step position.

The effects of flow structure on the separation efficiency and pressure drop in a cyclone-type oil separator were investigated via Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES), and the results were compared with experiments. Compared with the RANS simulations, the LES results were more similar to the experimental data as they simulated the complex flow structure more realistically. Swirling flow with strong turbulent kinetic energy (TKE) at the top section hindered the flow of particles toward the separator wall. In addition, a decrease in tangential velocity along the wall at the bottom reduced the centrifugal force, resulting in a decreased separation efficiency as particles were able to flow directly toward the outlet. The LES also predicted the pressure drop slightly better than the RANS simulation did, due to increased pressure drop caused by collision of the flow with the helix and outlet tube, which led to the formation of vortical flow structures with strong TKE.

The main flow could be unsteady in flow fields of film cooling for several reasons such as flow interactions between the rotor and the stator in the turbine. Understanding the characteristics of the film-cooling flow with an unsteady flow is important in the design of gas turbines. The effects of 36-Hz pulsations in the main flow on the streamwise velocity distributions, turbulence statistics, and temperature fluctuations in the film-cooling flow from a cylindrical hole with an orientation angle are investigated by numerical methods. Large-eddy simulation (LES) results match the experimental data with an acceptable accuracy, whereas the Reynolds-averaged Navier–Stokes simulation (RANS) results show large deviations with the experimental data and the LES results. Under 36-Hz pulsations, the URANS results predict a weaker streamwise velocity of the coolant jet that blocks the main flow compared with the LES. With 36-Hz pulsations at the time-averaged blowing ratio of 0.5, urms, the root mean squared fluctuating velocity in the streamwise direction around the coolant core increased due to intensive mixing, and vrms, the root mean squared fluctuating velocity in the wall-normal direction, increased along the trajectory of the injected coolant. Moreover, wrms, the root mean squared fluctuating velocity in the spanwise direction, increased around the wall compared to those at a steady state. The dimensionless temperature fluctuations increased in the region of the core of the coolant compared with those at a steady state. When the orientation angle was 30°, the distribution of the results moved in the z-direction; however, the overall trend was similar to that of a simple angle.

Utilizing biological processes for hydrogen production via gasification is a promising alternative method to coal gasification. The present study proposes a dynamic simulation model that uses a one-dimensional heat-transfer analysis method to simulate a biohydrogen production system. The proposed model is based on an existing experimental design setup. It is used to simulate a biohydrogen production system driven by the waste heat from an integrated gasification combined cycle (IGCC) power plant equipped with carbon capture and storage technologies. The data from the simulated results are compared with the experimental measurement data to validate the developed model's reliability. The results show good agreement between the experimental data and the developed model. The relative root-mean-square error for the heat storage, feed-mixing, and bioreactor tanks is 1.26%, 3.59%, and 1.78%, respectively. After the developed model's reliability is confirmed, it is used to simulate and optimize the biohydrogen production system inside the IGCC power plant. The bioreactor tank's time constant can be improved when reducing the operating volume of the feed-mixing tank by the scale factors of 0.75 and 0.50, leading to a 15.76% and 31.54% faster time constant, respectively, when compared with the existing design.