Browsing by Subject "Flat plate"
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Item Geometric location and power distribution for discrete heat sources on a vertical flat plate with natural convection(2011-08) Jung, Inyeop; Da Silva, Alexandre K., 1975-The current development of consumer electronics, driven by the effort to manufacture smaller products with increased performance, has amplified the chance for inducing higher thermal stresses to these systems. In an effort to devise more effective cooling methods for these systems, many scholars have studied the convective cooling of discrete heating elements. This report discusses a methodology for fabricating and testing a suitable flat plate design with discrete heating elements for both natural and forced convection cooling experiments. There were two plate design attempts: (i) an aluminum plate and (ii) a R3315 hydrostatic-resistance plastic foam plate. For the purpose of conducting experiments for the discrete heating elements, the foam plate design was found to be an appropriate design. After designing a proper foam plate, several experiments were conducted for the natural convection case. The combination of parameters such as the geometric location and power output ratio between heaters that resulted in the maximum thermal conductance were studied.Item Internal crossflow effects on turbine airfoil film cooling adiabatic effectiveness with compound angle round holes(2014-05) Klavetter, Sean Robert; Bogard, David G.Internal crossflow is an important element to actual gas turbine blade cooling; however, there are very few studies in open literature that have documented its effects on turbine blade film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of perpendicular crossflow on a row of 45 degree compound angle, cylindrical film cooling holes. Tests included a standard plenum condition, a baseline crossflow case consisting of a smooth-walled channel, and various crossflow configurations with ribs. The ribs were angled to the direction of prevailing internal crossflow at 45 and 135 degrees and were positioned at different locations. Experiments were conducted at a density ratio of DR=1.5 for a range of blowing ratios including M=0.5, 0.75, 1.0, 1.5, and 2.0. Results showed that internal crossflow can significantly influence adiabatic effectiveness when compared to the standard plenum condition. The implementation of ribs generally decreased the adiabatic effectiveness when compared to the smooth-walled crossflow case. The highest adiabatic effectiveness measurements were recorded for the smooth-walled case in which crossflow was directed against the spanwise hole orientation angle. Tests indicated that the direction of perpendicular crossflow in relation to the hole orientation can significantly influence the adiabatic effectiveness. Among the rib crossflow tests, rib configurations that directed the coolant forward in the direction of the mainstream resulted in higher adiabatic effectiveness measurements. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors are responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, jet exit velocity profiles, and in-hole vortices.Item Parameters that affect shaped hole film cooling performance and the effect of density ratio on heat transfer coefficient augmentation(2014-05) Boyd, Emily June; Bogard, David G.Film cooling is used in gas turbine engines to cool turbine components. Cooler air is bled from the compressor, routed internally through turbine vanes and blades, and exits through discrete holes, creating a film of coolant on the parts’ surfaces. Cooling the turbine components protects them from thermal damage and allows the engine to operate at higher combustion temperatures, which increases the engine efficiency. Shaped film cooling holes with diffuser exits have the advantage that they decelerate the coolant flow, enabling the coolant jets to remain attached to the surface at higher coolant flow rates. Furthermore, the expanded exits of the coolant holes provide a wider coolant distribution over the surface. The first part of this dissertation provides data for a new laidback, fan-shaped hole geometry designed at Pennsylvania State University’s Experimental and Computational Convection Laboratory. The shaped hole geometry was tested on flat plate facilities at the University of Texas at Austin and Pennsylvania State University. The objective of testing at two laboratories was to verify the adiabatic effectiveness performance of the shaped hole, with the intent of the data being a standard of comparison for future experimental and computational shaped hole studies. At first, measurements of adiabatic effectiveness did not match between the labs, and it was later found that shaped holes are extremely sensitive to machining, the material they are machined into, and coolant entrance effects. In addition, the adiabatic effectiveness was found to scale with velocity ratio for multiple density ratios and mainstream turbulence intensities. The second part of this dissertation measures heat transfer coefficient augmentation (hf/h0) at density ratios (DR) of 1.0, 1.2, and 1.5 using a uniform heat flux plate and the same shaped hole geometry. In the past, heat transfer coefficient augmentation was generally measured at DR = 1.0 under the assumption that hf/h0 was independent of density ratio. This dissertation is the first study to directly measure the wall and adiabatic wall temperature to calculate heat transfer coefficient augmentation at DR > 1.0. The results showed that the heat transfer coefficient augmentation was low while the jets were attached to the surface and increased when the jets started to separate. At DR = 1.0, hf/h0 was higher for a given blowing ratio than at DR = 1.2 and DR = 1.5. However, when velocity ratios are matched, better correspondence was found at the different density ratios. Surface contours of hf/h0 showed that the heat transfer was initially increased along the centerline of the jet, but was reduced along the centerline at distances farther downstream. The decrease along the centerline may be due to counter-rotating vortices sweeping warm air next to the heat flux plate toward the center of the jet, where they sweep upward and thicken the thermal boundary layer. This warming of the core of the coolant jet over the heated surface was confirmed with thermal field measurements.Item Reducing turbulence- and transition-driven uncertainty in aerothermodynamic heating predictions for blunt-bodied reentry vehicles(2014-08) Ulerich, Rhys David; Moser, Robert deLanceyTurbulent boundary layers approximating those found on the NASA Orion Multi-Purpose Crew Vehicle (MPCV) thermal protection system during atmospheric reentry from the International Space Station have been studied by direct numerical simulation, with the ultimate goal of reducing aerothermodynamic heating prediction uncertainty. Simulations were performed using a new, well-verified, openly available Fourier/B-spline pseudospectral code called Suzerain equipped with a ``slow growth'' spatiotemporal homogenization approximation recently developed by Topalian et al. A first study aimed to reduce turbulence-driven heating prediction uncertainty by providing high-quality data suitable for calibrating Reynolds-averaged Navier--Stokes turbulence models to address the atypical boundary layer characteristics found in such reentry problems. The two data sets generated were Ma[approximate symbol] 0.9 and 1.15 homogenized boundary layers possessing Re[subscript theta, approximate symbol] 382 and 531, respectively. Edge-to-wall temperature ratios, T[subscript e]/T[subscript w], were close to 4.15 and wall blowing velocities, v[subscript w, superscript plus symbol]= v[subscript w]/u[subscript tau], were about 8 x 10-3 . The favorable pressure gradients had Pohlhausen parameters between 25 and 42. Skin frictions coefficients around 6 x10-3 and Nusselt numbers under 22 were observed. Near-wall vorticity fluctuations show qualitatively different profiles than observed by Spalart (J. Fluid Mech. 187 (1988)) or Guarini et al. (J. Fluid Mech. 414 (2000)). Small or negative displacement effects are evident. Uncertainty estimates and Favre-averaged equation budgets are provided. A second study aimed to reduce transition-driven uncertainty by determining where on the thermal protection system surface the boundary layer could sustain turbulence. Local boundary layer conditions were extracted from a laminar flow solution over the MPCV which included the bow shock, aerothermochemistry, heat shield surface curvature, and ablation. That information, as a function of leeward distance from the stagnation point, was approximated by Re[subscript theta], Ma[subscript e], [mathematical equation], v[subscript w, superscript plus sign], and T[subscript e]/T[subscript w] along with perfect gas assumptions. Homogenized turbulent boundary layers were initialized at those local conditions and evolved until either stationarity, implying the conditions could sustain turbulence, or relaminarization, implying the conditions could not. Fully turbulent fields relaminarized subject to conditions 4.134 m and 3.199 m leeward of the stagnation point. However, different initial conditions produced long-lived fluctuations at leeward position 2.299 m. Locations more than 1.389 m leeward of the stagnation point are predicted to sustain turbulence in this scenario.