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In this study, the whisker structure of a harbor seal is applied to the lip and the trailing edge of a turbine cooling blade with a pressure-side cutback. Four cases are studied in this article, including a prototype, a whisker trailing edge, a PP (The lip's peak and the trailing edge's peak are designed at the same blade height) case, and a PV (The lip's peak and the trailing edge's valley are designed at the same blade height) case. The DDES method is used to simulate the flow and thermal mixing process in the cascade. The coolant mass flow ratios ( c m ) of 0.5% and 1% at an outlet Mach number of 0.9 are simulated. The PP case can achieve the best aerodynamic performance, which reduces the thermodynamic energy loss coefficient of the prototype by 0.98% and 0.99% at c m = 0.5% and c m = 1%, respectively. The PP case and the PV case increase the lowest spanwise average adiabatic film cooling effectiveness on the cutback surface from 0.5 to 0.7 at c m = 0.5%. The film cooling effectiveness of the PP case and the PV case can remain close to 1 over the entire cutback surface at c m = 1%. The PP case transforms the trailing edge shedding vortices on the pressure side into hairpin vortices. The whisker lip suppresses the lip vortex and alters the closed separation bubble on the cutback surface, causing the coolant to converge toward Section 1. The convergence of coolant is more helpful for the PP case to control the pressure side shedding vortex, resulting in a lower thermodynamic energy loss. [ABSTRACT FROM AUTHOR]

In this work, a fast and efficiently design method has been introduced. This design process consists of the overall design and the detailed design. For the overall design, one-dimensional pipe-network computations are employed to obtain several design cases quickly at the beginning. Meanwhile the solid domain geometry and mesh with cooling structures, i.e., film holes, impingement holes, and ribs have been generated to carry out three-dimensional (3-D) heat conduction calculations. Based on the above, a detailed design has been performed by 3-D conjugate heat transfer calculations. The results show that both the average temperature and the mass flow maximum errors between the pipe-network and 3-D conjugate heat transfer calculations are about 10%. In this article, the cooling structure of a gas turbine blade is designed with this platform. The final design results show that the maximum dimensionless temperature on the blade surface is 0.813, i.e., lower than the design requirement. The dimensionless mass flow rate in the first cooling inlet is 0.0168, and the mass flow rate in the secondary inlet is 0.0231. [ABSTRACT FROM AUTHOR]

This study investigates the internal cooling processes affected by the tip bleed holes in gas turbine blades. Double bleed holes are fixed at the center of the blade tip near the pressure side and suction side, respectively. Five different arrangements of the holes along the center line of the tip are studied. The purely double holes are set as the Baseline. The purpose of the present study is to provide a new perspective of the tip film cooling to understand the internal flow processes, vorticity evolution and the mechanism of the heat transfer augmentation. A topological analysis and the boundary layer analysis methods are introduced to better understand the tip heat transfer. The total extraction area and volume is kept at the same level for all the studied cases. The results show that the Dean vortices and the near-wall vortices induced by the secondary flow contribute to the high heat transfer coefficient on the tip surface. The mixing effect of the Dean vortices and the hole extraction helps to enhance heat transfer upstream of the tip. Different arrangement of the bleed holes can affect the internal flow processes and heat transfer performance. The suction effect of the center-line bleed hole can accelerate the near-hole flow and reduce the thickness of the boundary layer. The center-line hole fitted at the middle of the tip affects significantly the rear side of the hole. Thus, the holes aligned in the middle of the tip provide the highest heat transfer and thermal performance. The thermal performance is enhanced by up to 4.7% compared with the Baseline. [ABSTRACT FROM AUTHOR]

A numerical method is utilized to investigate the converging angle effects on the flow structure and heat transfer of a pin fin wedge duct with dimples/protrusions. The studied converging angles are and The results show that a pin fin-dimple wedge duct with larger converging angle produces higher heat transfer enhancement due to flow acceleration, increase of the impingement region, and shrinkage of the flow recirculation region, but it is also accompanied with a much larger friction factor. A pin fin-protrusion wedge duct with larger converging angle yields higher heat transfer augmentation due to flow acceleration and more intense impingement on the protrusion but it is also associated with larger pressure penalty. [ABSTRACT FROM AUTHOR]

The present study aims to improve cooling performance over the leading edge surface with the high temperature and high thermal stress by the introduction of trenched holes. Three staggered rows of leading-edge film cooling holes with different trench arrangements and hole orientations are included under blowing ratios of 0.5, 1.0, 1.5, and 2.0, compared with round-hole cases. Under the conditions of leading-edge flow patterns and convex curvature, the trenched hole with 2D width plays a role of "protection" of coolant against the impinging hot gas at a large range of blowing ratios. This contributes to the better lateral spread of coolant and cooling performance. Besides, the trenched holes narrow the regions with a high heat transfer coefficient and reduce the detrimental heating on the surface. Compared with round holes, the trenched holes guarantee the downstream coolant coverage and higher cooling performance at a larger inclined angle, in spite of the changed compound angles. [ABSTRACT FROM AUTHOR]

The realizable turbulence model was used to calculate flow and heat transfer characteristics in a rotating rectangular duct with detached pin fins in staggered arrangement. Transverse and longitudinal spacings of the pin fins were  2.5 D and  2.5 D, respectively. Reynolds number was 7,000 and Rotation number (Ro) varied from 0 to 1 while the clearance ranged from 0 to 0.5. Streamlines, vortex structure, wall shear stresses and Nusselt numbers were obtained. Flow phenomenon at the pin fin rear side and a leakage vortex near the pin fin tip were observed. High Nusselt numbers appeared on leading side. The leakage vortex imposed high energy losses in the mainflow. The flow and heat transfer characteristics were associated with Ro number and clearance. Middle values of Ro and clearance induced highest Nusselt numbers on leading side. However, high Ro and small clearance gave highest Nusselt numbers on trailing side. [ABSTRACT FROM AUTHOR]

A numerical method is employed to study effects of convergence angle and dimple shape on flow structure and heat transfer under a rotating frame. The investigated convergence angles are 0.0°, 6.3°, and 12.7°. The dimple shapes are circular, streamwise-elliptical, and spanwise-elliptical. The rotation number ranges from 0.0 to 0.4. Computed flow structures and heat transfer are compared. Higher rotation number generates better heat transfer in the dimple-pin wedge duct. The rotation direction also affects the flow structure and heat transfer. The spanwise-elliptical dimple shape shows best heat transfer augmentation as it generates the strongest vortex structure and turbulent kinetic energy in the dimples. Larger convergence angles exhibit larger Nusselt numbers and better heat transfer enhancement. Effects of the Coriolis force are considered as this force has favorable effects on enhancing the heat transfer on the surface it acts on. [ABSTRACT FROM AUTHOR]

A numerical study is performed to investigate the effects of jet hole shape and channel geometry on impingement cooling for both stationary and rotating condition. Two hole shapes and two channel geometries are introduced to counteract the adverse effects of centrifugal force and Coriolis force which are induced by rotation. Both the fluid and solid part are considered for realizing the conjugate heat transfer simulation. The unsteady k-ω SST turbulence model was employed to obtain the time-averaged Nusselt number distributions, time-averaged temperature and temperature gradient fields and the turbulent flow structure. The results show that the cooling jet from the racetrack-shaped hole can effectively withstand the intensive streamwise crossflow to enhance the heat transfer. The double swirling chamber (DSC) channel significantly improves the heat transfer characteristics on the cambered surface and diminishes the adverse effects of the Coriolis force. The high Nu number region is expanded while the temperature uniformity is improved. The combination of the racetrack-shaped hole and DSC channel provides the highest heat transfer among the four cases. The averaged Nu numbers on both the leading and trailing sides for all tested cases show obvious downtrend as rotation number increases, especially at high Reynolds number. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations are performed to investigate the effect of dimple location on the flow structure and heat transfer characteristics in a 90°-turned channel with pin fins. Results of the flow structure, heat transfer on the endwall, and friction factor are included in this study. It is found that the dimple location has an impact on the flow structure and heat transfer both for the pin fins arranged with in-line and staggered layout. The horseshoe vortex near the pin fin is influenced by the location of the dimple. The dimple enhances the Nusselt number on the endwall surface significantly. In addition, the dimple location has an effect on the low-speed recirculation, impingement, and vortex which are generated by the dimple. However, the dimple has very limited effects on the friction factor for all cases. It is also found that the area goodness factor and volume goodness factor are improved by the dimple. [ABSTRACT FROM AUTHOR]

Improved understanding of the impact of the operating conditions on the heat transfer and fluid flow behaviors of an outlet guide vane (OGV) is essential for accurate prediction of the lifetime of jet engines. In this article, the heat transfer characteristics of an OGV at various Reynolds numbers (Re), free stream turbulence levels, Mach number (Ma), and surface roughness are studied numerically. The Re is kept at 300,000 and 450,000, respectively, the free stream turbulence intensity ranges from 3.2% to 13%, and the turbulent length scale is varied from 1.2 to 11 mm. The Ma is selected as 0.06, 0.25, and 0.35, and the sandy grain roughness height is increased from the smooth wall level up to 160 µm. Mid-span pressure coefficient and Nu distributions are presented. Basically, the heat transfer patterns and pressure profiles are weak functions of the Re and Ma. Increasing the Re slightly moves the transition position upstream, while the Ma has no effect on the transition process. On the suction side, the transition is induced by flow separation and a bump is visible in the pressure profile. However, the turbulence intensity, turbulence length scale, and surface roughness levels have significant effects on the heat transfer and pressure distributions. On the suction side, the bump is invisible and the “separation-induced transition” is replaced by the “by pass transition”. It is also found that the transition position moves upstream as the turbulence intensity, length scale, and roughness level increase. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations are conducted to investigate the effects of bowed outlet guide vanes (OGVs) on endwall heat transfer and aerodynamic performance. Both on- and off-design conditions are studied. For bowed vanes, the bowed angle varies from 10° to 40° and the normalized bowed height ranges from 0.1 to 0.3. Results are included for Nusselt number distributions on the endwall, the energy losses, the yaw angles, and near-wall flow structures. For the convenience of comparison, the straight vane is also studied as a baseline. It is found that the bowed vanes can effectively reduce the endwall heat transfer. Among the tested parameters, a bowed angle of 40° and a normalized bowed height of 0.3 provide the best-controlled heat transfer for both the on- and off-design conditions. However, the bowed vanes have different effects on the energy losses and the yaw angles depending on the operating conditions. For the on-design condition with the inlet angle of 30° (the incidence angle is 0°) and the off-design condition with the inlet angle of 0°, the bowed vanes do not significantly increase the energy losses and yaw angles, whereas for the off-design condition with the inlet angle of −30°, significant changes are observed. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations are conducted to investigate the effects of dimple positions on the endwall heat transfer and friction factor in a pin fin wedge duct. The dimple diameter is the same as the pin fin diameter, while the ratio between dimple depth and dimple diameter is 0.2. Three different dimple positions are investigated (i.e., directly upstream of the pin fins, in a staggered manner relative to the pin fins, or in line with the pin fins. The Reynolds number ranges from 10,000 to 50,000. Results for endwall Nusselt number, friction factor, and flow structure are included. For convenience of comparison, the pin fin wedge duct without dimples is studied as baseline. It is found that dimples can effectively enhance endwall heat transfer. Among the tested parameters, the dimple position in line with the pin fins provides the best heat transfer enhancement, with low friction factor penalty. However, the various dimple positions have distinct effects on the friction factor depending on the flow structure near the dimple zone. For the first position, the friction factor is markedly increased due to flow impingement, recirculation, and mixing, while for the second and third positions, the friction factor is changed slightly due to different flow behaviors. [ABSTRACT FROM AUTHOR]