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Roughness, in various distributions and on various scales, is widely encountered in turbine modules and has a complex modulating effect on the distribution of film cooling effectiveness. In this study, the fast-response pressure-sensitive paint technique was utilized to analyze the steady and unsteady behaviors of film cooling effectiveness under various roughness conditions. Two roughness conditions (upstream roughness and the combination of upstream and downstream roughness) were examined at three roughness scales (ks/D = 0.016, 0.129, and 0.782) and three blowing ratios (M = 0.5, 1.0, and 1.5). Comparisons of the steady behaviors of cooling effectiveness revealed that upstream roughness was the primary factor influencing cooling effectiveness for the adequate film attachment (M = 0.5 and 1.0) and that the cooling effectiveness deteriorated with rising ks/D. Downstream roughness improved the cooling effectiveness in cases with poor film attachment (M = 1.5). Considering that the distribution of film cooling effectiveness is modulated by the vortical structures of jet in crossflow, the unsteady behaviors of roughness-affected cooling effectiveness were analyzed through proper orthogonal decomposition. Upstream roughness influenced the counter-rotating vortex pair and horseshoe vortex (HV) signatures by separately widening and shortening the patterns in the lateral and streamwise directions, a trend that became more pronounced with increasing ks/D values. Moreover, larger roughness scales at lower blowing ratios caused asymmetry in the signatures. Downstream roughness primarily affected the signatures through local morphological variations, inducing oscillations in modal patterns. For attached films, downstream roughness had a nonsignificant impact, while for detached films, disturbances caused by downstream roughness resulted in vague and asymmetric modal patterns. Evaluation of the reconstructed cooling effectiveness revealed that roughness tended to affect the unsteady behavior of HV-modulated cooling effectiveness at high frequencies. These clarified steady and unsteady behaviors across various roughness conditions provide references for improving film-cooling structures to accommodate diversely roughened turbine modules. [ABSTRACT FROM AUTHOR]

In the present study, we conducted a conjugate heat transfer (CHT) analysis for double-wall cooling with impingement and effusion, incorporating various types of ribs, using the Reynolds-averaged Navier–Stokes (RANS) method and the modified shear stress transport (SST) turbulence closure model (SST-KIC), accounting for the Kato-Launder modification (K), intermittency (I), and crossflow (C) transition effects. We comprehensively discussed the impact of slit type (parallel, inclined, convergent, and divergent), open-area ratio (β = 5%, 20%, and 40%), and jet Reynolds number on the turbulent flow and heat transfer in a double-wall cooling with slit ribs. Our findings indicated that the introduction of slit ribs significantly improved heat transfer and its uniformity on the target wall, albeit with a slight increase in pressure loss. The overall Nusselt number and thermal-hydraulic performance (THP) in cases with slit ribs gradually decreased with β, yet remained up to 17% and 13% higher than those observed on a smooth target wall. Notably, the open-area ratio of the slit rib exhibited a more pronounced effect on heat transfer over the target plate. For the divergent slit rib within the Reynolds number range of 4000–16 000, the heat transfer enhancement ratio reached the highest value at β of 0.05. In addition, we computed the entropy production caused by fluid friction and heat transfer, as well as the overall entropy production in double-wall cooling at different β and Re. The analysis revealed that the slit rib target plate performed better than the solid rib target plate, showing a distinct advantage in terms of total entropy production. [ABSTRACT FROM AUTHOR]

In high-speed rotating channels, significant compressive effects are observed, resulting in distinct flow characteristics compared to incompressible flows. This study employs a finite volume method, based on the implicit formulation, to solve for low-speed compressible laminar flow in rotating channels using an orthogonal uniform grid. The governing equations include the full Navier–Stokes equations and the energy equation. The alterations in flow within rotating channel are primarily influenced by the compressive effects of centrifugal force and the compressibility of fluid within the flow's normal section. The first effect involves a reduction in the velocity due to centrifugal force, leading to an increasing influence of the Coriolis force compared to inertial forces. This trend change aligns closely with the increase in rotation speed. The second effect arises from the increase in the rotating Mach number and the Coriolis compression, resulting in slight density differences within the cross section. Strong centrifugal forces generate significant centrifugal additional force (buoyancy force). Consequently, under the same local rotation number, the velocity profiles of the mainstream experience considerable changes. Additionally, a higher rotating Mach number significantly impacts wall shear stress, with the leading side being notably affected. For instance, at cross-sectional Ro = 0.6 and MaΩ = 2.1, the dimensionless shear stress on the leading side decreased by 13%. Furthermore, while an increase in the rotating Mach number has minimal impact on the cross-sectional secondary flow structure, changes in mainstream velocity profiles influence secondary flow intensity, resulting in an enhanced velocity peak and a shift toward the trailing side. [ABSTRACT FROM AUTHOR]

With the aim of exploring the particle transport and deposition characteristics in the internal cooling channel of turbine blades, the computational fluid dynamics-discrete element method is used to implement the numerical simulation of particle transport and deposition in the impingement-film cooling passage. First, the unsteady development process of the particle transport and deposition with the increase in injection particle mass is obtained. Then, the effect of jets Reynolds number, particle Stokes number, and initial particle volume fraction on the particle deposition characteristics is presented. Finally, the particle deposition mechanism in the impingement-film cooling passage of turbine blades is revealed. The results show that the conical-shape particle deposition layer is formed at the impingement stagnation point region and the banded-shape particle deposition layer is formed between adjacent impingement holes. The cooling gas carrying particles is injected from the impact hole and subjected to the fluid shear force. Then, the cooling gas carrying particles gradually developed into the conical-shape free jets. In addition, the symmetrical vortex structure is formed due to the collision of the adjacent jets. Therefore, the particle deposition layer is formed on the impingement target surface, which is caused by the energy attenuation due to the continuous collision of the particle with the particle and the particle with the wall. The increase in the jets Reynolds number inhibits the particle deposition behavior, and the increase in the Stokes number accelerates the particle deposition behavior. [ABSTRACT FROM AUTHOR]