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Boudet Jérôme, Cahuzac Adrien, Kausche Philip, et al. Zonal Large-Eddy Simulation of a Fan Tip-Clearance Flow, With Evidence of Vortex Wandering J. Turbomach. 137, 061001 (2015) (9 pages);   Paper No: TURBO-13-1240;   doi:10.1115/1.4028668

The flow in a fan test-rig is studied with combined experimental and numerical methods, with a focus on the tip-leakage flow. A zonal RANS/LES approach is introduced for the simulation: the region of interest at tip is computed with full large-eddy simulation (LES), while Reynolds-averaged Navier–Stokes (RANS) is used at inner radii. Detailed comparisons with the experiment show that the simulation gives a good description of the flow. In the region of interest at tip, a remarkable prediction of the velocity spectrum is achieved, over about six decades of energy. The simulation precisely captures both the tonal and broadband contents. Furthermore, a detailed analysis of the simulation allows identifying a tip-leakage vortex (TLV) wandering, whose influence onto the spectrum is also observed in the experiment. This phenomenon might be due to excitation by upstream turbulence from the casing boundary layer and/or the adjacent TLV. It may be a precursor of rotating instability. Finally, considering the outlet duct acoustic spectrum, the vortex wandering appears to be a major contribution to noise radiation.

Gomatam Ramachandran Saiprashanth, Shih Tom I-P. Biot Number Analogy for Design of Experiments in Turbine Cooling J. Turbomach. 137, 061002 (2015) (14 pages);   Paper No: TURBO-14-1080;   doi:10.1115/1.4028327

Cooling of turbine components that come in contact with the hot gases strongly affects the turbine's efficiency and service life. Designing effective and efficient cooling configurations requires detailed understanding on how geometry and operating conditions affect the way coolant cools the turbine materials. Experimental measurements that can reveal such information are difficult and costly to obtain because gas turbines operate at high temperatures (up to 2000 K), high pressures (30+ bar), and the dimensions of many key features in the cooling configurations are small (millimeters or smaller). This paper presents a method that enables experiments to be conducted at near room temperatures, near atmospheric pressures, and using scaled-up geometries to reveal the temperature and heat-flux distributions within turbine materials as if the experiments were conducted under engine operating conditions. The method is demonstrated by performing conjugate computational fluid dynamics (CFD) analyses on two test problems. Both problems involve a thermal barrier coating (TBC)-coated flat plate exposed to a hot-gas environment on one side and coolant flow on the other. In one problem, the heat transfer on the coolant side is enhanced by inclined ribs. In the other, it is enhanced by an array of pin fins. This conjugate CFD study is based on 3D steady Reynolds-averaged Navier–Stokes (RANS) closed by the shear-stress-transport turbulence model for the fluid phase and the Fourier law for the solid phase. Results obtained show that, of the dimensionless parameters that are important to this problem, it is the Biot number that dominates. This study also shows that for two geometrically similar configurations, if the Biot number distributions on the corresponding hot-gas and coolant sides are nearly matched, then the magnitude and contours of the nondimensional temperature and heat-flux distributions in the material will be nearly the same for the two configurations—even though the operating temperatures and pressures differ considerably. Thus, experimental measurements of temperature and heat-flux distributions within turbine materials that are obtained under “laboratory” conditions could be scaled up to provide meaningful results under “engine” relevant conditions.

Niether Sebastian, Bobusch Bernhard, Marten David, et al. Development of a Fluidic Actuator for Adaptive Flow Control on a Thick Wind Turbine Airfoil J. Turbomach. 137, 061003 (2015) (10 pages);   Paper No: TURBO-14-1229;   doi:10.1115/1.4028654

Wind turbines are exposed to unsteady incident flow conditions such as gusts or tower interference. These cause a change in the blades' local angle of attack, which often leads to flow separation at the inner rotor sections. Recirculation areas and dynamic stall may occur, which lead to an uneven load distribution along the blade. In this work, a fluidic actuator is developed that reduces flow separation. The functional principle is adapted from a fluidic amplifier. High pressure air fed by an external supply flows into the interaction region of the actuator. Two control ports, oriented perpendicular to the inlet, allow for a steering of the actuation flow. One of the control ports is connected to the suction side, the other to the pressure side of the airfoil. Depending on the pressure difference that varies with the angle of attack, the actuation air is directed into one of four outlet channels. These guide the air to different chordwise exit locations on the airfoil's suction side. The appropriate actuation location adjusts automatically according to the pressure difference between the control ports and therefore incidence. Suction side flow separation is delayed as the boundary layer is enriched with kinetic energy. Experiments were conducted on a DU97-W-300 airfoil at Re = 2.2 × 105. Compared to the baseline, lift variations due to varying angles of attack were reduced by an order of magnitude. A Fast/Aerodyn simulation of a full wind turbine rotor was performed to show the real world load reduction potential. Additionally, system integration is discussed, which includes suggestions on producibility and operational details.

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