Search Results (18)

This study introduces the Gyroid structure, a type of triply periodic minimal surface (TPMS), for enhanced effusion cooling performance. Conjugate heat transfer simulations are used to compare the flow behavior, pressure loss, and overall cooling effectiveness of single- and double-wall Gyroid configurations against a baseline film hole model at blowing ratios of 0.5–2.0. Results show that the Gyroid design eliminates jet lift-off and counter-rotating vortex pairs, ensuring full coolant coverage and a thicker coolant layer than the baseline. The double-wall configuration further improves cooling with jet impingement, yielding higher average Nusselt numbers than the single-wall design. At equal pressure loss, the impingement/Gyroid model outperforms the baseline by 102.7% in cooling effectiveness. To assess manufacturability, a high-resolution CT scan is used to validate a laser powder bed fusion-printed Gyroid sample at gas turbine blade scale, confirming feasibility for industrial application. These findings highlight the superior thermal performance and manufacturability of the 3D-printed Gyroid structure, offering a promising cooling solution for next-generation turbine blades. Full article

To pursue higher thermal efficiency in aero gas turbines, the contradiction between extreme high-temperature conditions and material temperature resistance limits has made advanced thermal management technologies crucial. Effusion cooling is a technique that utilizes a large number of small holes (around 0.1 mm in diameter) to cool more effectively. Through numerical simulation, the current research investigates the impact of different parameters on the effectiveness of effusion cooling, including porosities (φ), blowing ratios (Br), height of the porous structure (H), thermal conductivity (λ) of the porous structures, and the ratios of the mainstream temperature to the coolant temperature (R_t). The results show that with the increased porosity, the cooling effectiveness of the porous structure surface first increases and then decreases, while the averaged cooling effectiveness downstream of the mainstream gradually increases. The first two parameters have the greatest influence on the cooling effectiveness. And there is a positive relationship between the blowing ratios and cooling effectiveness, meaning that higher blowing ratios lead to greater cooling effectiveness. A larger height and a smaller thermal conductivity coefficient cause a non-uniform temperature distribution. Different temperature ratios have little influence on coolant coverage pattern. Finally, a correlation is built to predict the cooling effectiveness considering all the parameters which provides fundamental references for the application of effusion cooling. Full article

Power electronics convert and control electrical power in applications ranging from electric motors to telecommunications and computing. Ongoing efforts to miniaturize these systems and boost power density demand advanced thermal management solutions to maintain optimal cooling and temperature control. Spray cooling offers an effective means of removing high heat fluxes and keeping power electronics within safe operating temperatures. This study presents an experimental investigation of flash spray cooling in a closed-loop system using R410A refrigerant. In particular, two nozzles with different spraying angles are used to study the effects of the distance between the spray nozzle and a heated flat surface, as well as the mass flow rate of the coolant. Results indicate that three key flow-pattern factors—surface coverage, impingement intensity, and liquid film dynamics—govern the heat transfer mechanisms and determine cooling efficiency. Flash spray cooling using refrigerants like R410A demonstrates strong potential as a high-performance thermal management strategy for next-generation power electronics. Full article

Magnetite (Fe₃O₄) provides a protective corrosion layer in the steam generators of nuclear power plants. The presence of monoethanolamine (MEA) in coolant water has a beneficial effect on corrosion processes. In that context, the adsorption of MEA and ethanol–ammonium cation on the {111} surface of magnetite was studied using the molecular dynamics (MD) method. A modified version of the mechanical force field (ClayFF) was used. The systems were simulated at different temperatures (423 K; 453 K; 503 K). Surface coverage data were obtained from adsorption simulations; the root-mean-square deviation (RMSD) of the target molecules were calculated, and their minimum distance to the magnetite surface was traced. The potential and adsorption energies of MEA were calculated as a function of temperature. It has been established that the interaction between MEA and magnetite is due to electrostatic phenomena and the adsorption rate increases with temperature. A comparison was made with existing experimental results and similar MD simulations. Full article

The study of low-speed jets into crossflow is critical to the performance of gas turbines. Film cooling is a method to maintain manageable blade temperatures in turbine sections while increasing turbine inlet temperatures and turbine efficiencies. Initially, cooling holes were cylindrical. Film cooling jets from these discrete round holes were found to be very susceptible to jet liftoff, which reduces surface effectiveness. Shaped holes have become prominent for improved coolant coverage. Fan-shaped holes are the most common design and have shown good improvement over round holes. However, fan-shaped holes introduce additional parameters to the already complex task of modeling cooling effectiveness. Studies of these flows range in hole lengths from those found in actual turbine blades to very long holes with fully developed flow. The flow within the holes themselves is difficult to study as there is limited optical access. However, the flow within the holes has a strong effect on the resulting properties of the jet. This study presents velocity and vorticity fields measured using high-resolution magnetic resonance velocimetry (MRV) to study three different fan-shaped hole geometries at two blowing ratios. Because MRV does not require line of sight, it provides otherwise hard-to-obtain experimental data of the flow within the film cooling hole in addition to the mainflow measurements. By allowing measurement within the cooling hole, MRV shows how a poor choice of diffuser start point and angle can be detrimental to film cooling if overall hole length and cooling flow velocity are not properly accounted for in the design. The downstream effect of these choices on the jet height and counter-rotating vortex pair is also observed. Full article

The spatiotemporal evolution of the flow structures and coolant coverage of double-row film cooling with upstream forward jets and downstream backward jets, having a significant impact on film-cooling performance, is studied using the simplified thermal lattice Boltzmann method (STLBM). Moreover, the effect of the inclination angle of downstream backward jets is considered. The high-performance simulations of film cooling have been conducted by using our verified in-house solver. Results show that special flow structures, such as a sand dune-shaped protrusion, appear in double-row film cooling with upstream forward jets and downstream backward jets, which is mainly because of the blockage effect resulting from the coolant jet with backward injection. The interaction among structures results in the generation of an anti-counterrotating vortex pair (anti-CVP). The anti-CVP with the downwash motion can result in the attachment of coolant to the bottom wall, which promotes the stability and lateral coverage of coolant film. The momentum and heat transport are strengthened as the backward jet is injected into the boundary layer of the mainstream. Although the downstream evolution of the backward jet is not very smooth, its core attaches closely to the bottom wall due to the downwash motion of anti-CVP. Moreover, there is an obvious backflow zone shown in the trailing edge of the downstream backward jet with a large inclination angle. The obvious backflow makes the coolant attach to the bottom wall well. Therefore, the film cooling effectiveness is improved as the inclination angle of the downstream backward jet varies from ${\alpha }_{down}=135°$ to ${\alpha }_{down}=155°$, with a constant blowing ratio of $BR=0.5$. In addition, the fluctuation of the bottom wall’s temperature is weak due to the stable coverage of the coolant layer under ${\alpha }_{down}=155°$. The film-cooling performance with an inclination angle of ${\alpha }_{down}=155°$ is the best among all the cases studied in this work. This work provides essential insights into film cooling with backward coolant injection and contributes to obtaining a complete understanding of film cooling with backward coolant injection. Full article

A novel modification method, the ‘micro-scale’ rib, is proposed to expand cooling coverage for turbine endwalls. However, the introduction of the rib will inevitably affect the flow in the near-wall region. Therefore, the variation in the flow pattern for the traditional model of secondary flow needs further exploration. In this paper, to gain a clearer understanding of the micro-scale rib, the original endwall and three types of ribbed endwalls were adopted to numerically present the detailed flow, film cooling, and heat transfer information for the endwall surface and phantom cooling on the suction side (SS) of the blade. The Ansys code CFX was utilized to solve the 3D Reynolds-averaged Navier–Stokes (RANS) equations, and the SST k-ω was selected as the turbulence model after the verification. The results show that the rib-like vortex changed the flow of the coolant and had various impacts on the cooling characteristics. Although the cooling performance of the ribbed endwall improved, it also had a negative impact on heat transfer in most cases. Compared with the original, the vertical rib cases provided optimal film cooling, with increases of 26.9% and 17.4% for rib spacing values of 8 mm and 10 mm, respectively, with little difference in heat transfer (less than 1%). In addition, the horizontal rib cases presented the worse performance for both film cooling and heat transfer, which indicates that the rib layout should consider a mainstream flow direction for future designs. Full article

Due to machining techniques and dust deposition, gas turbine upstream slots and vane roots are always filleted, significantly affecting the cooling performance of the endwall. The effects of upstream slot fillet and vane root fillet on the cooling performance of the gas turbine endwall were investigated by solving the three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations with the shear stress transport (SST) k–ω turbulence model. The results indicate that the velocity distribution of the slot coolant is effectively changed by introducing the upstream slot fillets. Among the four cases, the largest adiabatic cooling effectiveness was obtained for the case with two similar fillets, with a 42% increase in effective cooling area compared to the traditional slot. At MFR = 0.75%, the horseshoe vortex is weakened by the introduction of the vane fillet with a small radius, with a 53% increase in effective cooling area compared to the baseline. However, the vane fillet with a large radius makes the boundary layer flow separately prematurely, decreasing the cooling performance. The lateral coverage of the coolant jet from the filmhole embedded in the vane root fillet is greatly enhanced by increasing the vane root fillet radius. However, the streamwise coverage is decreased and the thermodynamic loss is increased. Full article

Heavy-duty vehicles, such as trucks or buses, typically have larger battery packs compared to passenger electric vehicles (EVs). These batteries generate more heat due to the increased power demands of the vehicle. Effective thermal management is therefore crucial to prevent excessive heat buildup and maintain optimal battery performance. This paper aimed to develop a dynamic and efficient cooling system for larger Li-ion batteries used in electric vehicles. In this study, we propose a novel cold plate design featuring a zig-zag serpentine flow pattern within a rectangular profile channel. The chosen design maximizes the coolant coverage over the cold plate’s surface area. To investigate the performance of the cold plate design, we designed and modeled a total of six different cold plates with varying numbers of channels (3, 5, 7, 9, 11, and 13). Preliminary simulations were conducted using Star CCM+ software. The cold plate material selected for its high thermal conductivity was aluminum, while water served as the coolant. Several parameters were optimized, including adjustments to channel width, mass flow rate, heat flux, and inlet coolant temperature. The optimization was conducted to determine the optimal design for the cold plate. We found that the best design configurations were five-channel with an 18 mm channel width and a seven-channel with a 16 mm channel width. It was found that the temperature rapidly increased and reached its maximum in the outlet region. In the design with three channels, the maximum temperature attained at the exit region was 330.84 K. The temperature gradually decreased at the exit region when the number of the channels increased from 3 channels to 13 channels and achieved a minimum temperature of 316 K for the design with 13 channels. For these configurations, heat fluxes of 2 °C and 3 °C were found to be optimal, while a discharge rate of 4 °C was deemed acceptable. The zig-zag design and the obtained results are instrumental in designing and evaluating the performance of cold plates by exploring various parameters. This research contributes to the development of an effective cooling system for large Li-ion batteries in EVs, potentially enhancing their efficiency and reliability. Full article

To protect turbine endwall from heat damage of hot exhaust gas, film cooling is the most significant method. The complex vortex structures on the endwall, such as the development of horseshoe vortices and transverse flow, affects cooling coverage on the endwall. In this study, the effects of gas thermophysical properties on full-range endwall film cooling of a turbine vane are investigated. Three kinds of gas thermophysical properties models are considered, i.e., the constant property gas model, ideal gas model, and real gas model, with six full-range endwall film cooling holes patterns based on different distribution principles. From the results, when gas thermophysical properties are considered, the coolant coverage in the pressure side (PS)-vane junction region is improved in Pattern B, Pattern D, Pattern E, and Pattern F, which are respectively designed based on the passage middle gap, limiting streamlines, heat transfer coefficients (HTCs), and four-holes pattern. Endwall η distribution is mainly determined by relative ratio of ejecting velocity and density of the hot gas and the coolant. For the cooling holes on the endwall with an injection angle of 30°, the density ratio is more dominant in determining the coolant coverage. At the injection angle of 45°, i.e., the slot region, the ejecting velocity is more dominant in determining the coolant coverage. When the ejecting velocity Is large enough from the slot, the coolant coverage on the downstream endwall region is also improved. Full article

Most power transformers are oil-immersed transformers for which its insulation system consists of oil and cellulosic solid. The insulation liquid impregnates the solid-covering air spaces, which improves the efficiency of the insulation system. Not only does the oil ensure electrical insulation but it also works as coolants transferring the heat generated during transformer operation to the exterior of the transformer. Throughout normal operation conditions, transformers experience multiple stresses that degrade their insulation. Since the lifetime of oil-immersed transformers is defined mainly by the state of the insulation paper, it is critical to understand the behavior and degradation mechanisms of new insulation systems that try to overcome the drawbacks of mineral oil as well as to improve power transformer performances. The current increased prevalence of the nonlinear loads additionally stresses power transformers, which generates their premature ageing or even failure. Consequently, new materials and assessment methods are required to guarantee the suitable management of power transformer populations. In this Special Issue “Experimental and Numerical Analysis of Thermal Ageing in Power Transformers”, four papers have been published. The guest editor also describes briefly some challenges involved beyond the coverage of this Special Issue. Full article

Single-row double-jet film cooling (DJFC) of a turbine guide vane is numerically investigated in the present study, under a realistic aero-thermal condition. The double-jet units are positioned at specific locations, with 57% axial chord length (C_x) on the suction side or 28% C_x on the pressure side with respect to the leading edge of the guide vane. Three spanwise spacings (Z) in double-jet unit (Z = 0, 0.5d, and 1.0d, here d is the film hole diameter) and four spanwise injection angles (β = 11°, 17°, 23°, and 29°) are considered in the layout design of double jets. The results show that the layout of double jets affects the coupling of adjacent jets and thus subsequently changes the jet-in-crossflow dynamics. Relative to the spanwise injection angle, the spanwise spacing in a double-jet unit is a more important geometric parameter that affects the jet-in-crossflow dynamics in the downstream flowfield. With the increase in the spanwise injection angle and spanwise spacing in the double-jet unit, the film cooling effectiveness is generally improved. On the suction surface, DJFC does not show any benefit on film cooling improvement under smaller blowing ratios. Only under larger blowing ratios does its positive potential for film cooling enhancement start to show. Compared to the suction surface, the positive potential of the DJFC on enhancing film cooling effectiveness behaves more obviously on the pressure surface. In particular, under large blowing ratios, the DJFC plays dual roles in suppressing jet detachment and broadening the coolant jet spread in a spanwise direction. With regard to the DJFC on the suction surface, its main role in film cooling enhancement relies on the improvement of the spanwise film layer coverage on the film-cooled surface. Full article

The interaction between the film-cooling jet and vortex structures in the turbine passage plays an important role in the endwall cooling design. In this study, a simplified topology of a blunt body with a half-cylinder is introduced to simulate the formation of the leading-edge horseshoe vortex, where similarity compared with that in the turbine cascade is satisfied. The shaped cooling hole is located in the passage. With this specially designed model, the interaction mechanism between the cooling jet and the passage vortex can therefore be separated from the crossflow and the pressure gradient, which also affect the cooling jet. The loss-analysis method based on the entropy generation rate is introduced, which locates where losses of the cooling capacity occur and reveals the underlying mechanism during the mixing process. Results show that the cooling performance is sensitive to the hole location. The injection/passage vortex interaction can help enhance the coolant lateral coverage, thus improving the cooling performance when the hole is located at the downwash region. The coolant is able to conserve its structure in that, during the interaction process, the kidney vortex with the positive rotating direction can survive with the negative-rotating passage vortex, and the mixture is suppressed. However, the larger-scale passage vortex eats the negative leg of the kidney vortices when the cooling hole is at the upwash region. As a result, the coolant is fully entrained into the main flow. Changes in the blowing ratio alter the overall cooling effectiveness but have a negligible effect on the interaction mechanism. The optimum blowing ratio increases when the hole is located at the downwash region. Full article

A new experimental study is presented for a combustor with a double-wall cooling design. The inner wall at the hot gas side features effusion cooling with 7-7-7 laidback fan-shaped holes, and the outer wall at the cold side features an impingement hole pattern with circular holes. Data have been acquired to assess the thermal and aerodynamic behavior of the setup using a new, scaled up, engine-similar test rig. Similarity includes Reynolds, Nusselt, and Biot numbers for hot gas and coolant flow. Different geometrical setups are studied by varying the cavity height between the two walls and the relative alignment of the two hole patterns at several different blowing ratios. This article focuses on the thermal performance of the setup. The temperature data are acquired using two infrared systems on either side of the effusion wall specimen. In addition to cooling effectiveness evaluations, finite element simulations are performed, yielding the locally resolved wall heat fluxes. Results are presented for three cavity heights and two longitudinal specimen alignments. The results show that the hot gas side total cooling effectiveness can achieve values as high as 90% and is mainly influenced by the effusion coverage. Impingement cooling has a small influence on overall effectiveness, and the area of influence is mainly located upstream where effusion cooling is not built up completely. The analyzed geometric variations show a major influence on cavity flow and impingement heat transfer. Small cavities lead to constrained flow and high local Nusselt numbers, while larger cavities show more equalized Nusselt number distributions. A present misalignment shows especially high influence at small cavity heights. The largest cavity height, in general, showed a decrease in heat transfer due to reduced jet momentum. Full article

This paper studied the combined influences of the hot streak and swirl on the cooling performances of the NASA C3X guide vane coated with or without thermal barrier coatings (TBCs). The results show that: (1) Even under uniform velocity inlet conditions, the hot streak core can be stretched as it impinges the leading edge which causes higher heat load on the suction side of the forward portion. (2) The swirl significantly affects circumferential and radial migration of the hot streak core in the NGV passage. On the passage inlet plane, positive swirl leads to a hotter tip region on the suction side. In comparison, negative swirl leads to a hotter hub region on the pressure side. (3) Under the influence of swirl, migration of coolant improves the coverage of film cooling close to the midspan, while in the regions close to the hub and tip end-wall, the overall cooling performance decreases simultaneously. (4) In the regions with enough internal cooling, the cooling effectiveness increment is always larger than that in other regions. Besides, the overall cooling effectiveness increment decreases on the region covered by film cooling for the coated vane, especially in the region with negative local heat flux. Full article