Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 98-100). Also available via the Internet.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Das, Suman; Committee Member: Halloran, John; Committee Member: Henderson, Clifford; Committee Member: Kalaitzidou, Kyriaki. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis--Technische Hogeschool Twente 1977.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 291-301).

A flow model for a Joukowsky airfoil with an inclined spoiler or split flap is constructed based on the early work by Parkinson and Jandali. No restriction is imposed on the airfoil camber, the inclination and length of the spoiler or split flap, and the angle of incidence. The flow is assumed to be steady, two-dimensional, inviscid and incompressible. A sequence of conformal transformations is developed to deform the contour of the airfoil and the spoiler (split flap) onto the circumference of the unit circle over which the flow problem is solved. The partially separated flow region behind these bluff bodies is simulated by superimposing suitable singularities in the transform plane. The trailing edge, the tip of the spoiler (flap) are made critical points in the mappings so that Kutta conditions are satisfied there. The pressures at these critical points are matched to the pressure inside the wake, the only empirical input to the model. Some studies of an additional boundary condition for solving the flow problem were carried out with considerable success. The chordwise pressure distributions and the overall lift force variations are compared with experiments. Good agreement in general is achieved. The model can be extended readily to airfoils of arbitrary profile with the application of the Theodorsen transformation. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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The concept of moving surface boundary-layer control, as applied to the Joukowsky and NACA airfoils, is investigated through a planned experimental program complemented by theoretical and flow visualization studies. The moving surface was provided by one or two rotating cylinders located at the leading edge, the trailing edge, or the top surface of the airfoil. Three carefully designed two-dimensional models, which provided a wide range of single and twin cylinder configurations, were tested at a subcritical Reynolds number (Re = 4.62 x 10⁴ or Re — 2.31 x 10⁵) in a laminar-flow tunnel over a range of angles of attack and cylinder rotational speeds. The test results suggest that the concept is indeed quite promising and can provide a substantial increase in lift and a delay in stall. The leading-edge rotating cylinder effectively extends the lift curve without substantially affecting its slope. When used in conjunction with a second cylinder on the upper surface, further improvements in the maximum lift and stall angle are possible. The maximum coefficient of lift realized was around 2.22, approximately 2.6 times that of the base airfoil. The maximum delay in stall was to around 45°. In general, the performance improves with an increase in the ratio of cylinder surface speed (Uc) to the free stream speed (U). However, the additional benefit derived progressively diminishes with an increase in Uc/U and becomes virtually negligible for Uc/U > 5. There appears to be an optimum location for the leading-edge-cylinder. Tests with the cylinder at the upper side of the leading edge gave quite promising results. Although the CLmax obtained was a little lower than the two-cylinder configuration (1.95 against 2.22), it offers a major advantage in terms of mechanical simplicity. Performance of the leading-edge-cylinder also depends on its geometry. A scooped configuration appears to improve performance at lower values of Uc/U (Uc/U ≤ 1). However, at higher rates of rotation the free stream is insensitive to the cylinder geometry and there is no particular advantage in using the scooped geometry. A rotating trailing-edge-cylinder affects the airfoil characteristics in a fundamentally different manner. In contrast to the leading-edge-cylinder, it acts as a flap by shifting the CL vs. α plots to the left thus increasing the lift coefficient at smaller angles of attack before stall. For example, at α = 4°, it changed the lift coefficient from 0.35 to 1.5, an increase of 330%. Thus in conjunction with the leading-edge- cylinder, it can provide significant improvements in lift over the entire range of small to moderately high angles of incidence (α ≤ 18°). On the theoretical side, to start with, the simple conformal transformation approach is used to obtain a closed form potential-flow solution for the leading-edge-cylinder configuration. Though highly approximate, the solution does predict correct trends and can be used at a relatively small angle of attack. This is followed by an extensive numerical study of the problem using: • the surface singularity approach including wall confinement and separated flow effects; • a finite-difference boundary-layer scheme to account for viscous corrections; and • an iteration procedure to construct an equivalent airfoil, in accordance with the local displacement thickness of the boundary layer, and to arrive at an estimate for the pressure distribution. Effect of the cylinder is considered either through the concept of slip velocity or a pair of counter-rotating vortices located below the leading edge. This significantly improves the correlation. However, discrepancies between experimental and numerical results do remain. Although the numerical model generally predicts CLmax with a reasonable accuracy, the stall estimate is often off because of an error in the slope of the lift curve. This is partly attributed to the spanwise flow at the model during the wind tunnel tests due to gaps in the tunnel floor and ceiling required for the connections to the externally located model support and cylinder drive motor. However, the main reason is the complex character of the unsteady flow with separation and reattachment, resulting in a bubble, which the present numerical procedure does not model adequately. It is expected that better modelling of the cylinder rotation with the slip velocity depending on a dissipation function, rotation, and angle of attack should considerably improve the situation. Finally, a flow visualization study substantiates, rather spectacularly, effectiveness of the moving surface boundary-layer control and qualitatively confirms complex character of the flow as predicted by the experimental data. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Uncertainty in accurately knowing applied internal heat transfer coefficients inside of a cooling passage can lead to variability in predicting low cycle fatigue life of a turbine vane or blade. Under-predicting a life value for a turbine part can have disastrous effects on the engine as a whole, and can negate efforts in innovative design for advanced cooling techniques for turbine components. Quantification of this fatigue life uncertainty utilizing a computational framework is the primary objective of this thesis. Through the use of probabilistic design methodologies a process is developed to simulate uncertainties of internal heat transfer coefficient, which are then applied to the aft section of a non-rotating turbine blade component, internally cooled through a multi-pass serpentine channel. While keeping all other parameters constant internal heat transfer coefficients are varied according to a prescribed uncertainty range throughout the passages. The effect on the low cycle fatigue life of the airfoil is then evaluated at three discrete locations: near the base of the airfoil, towards the tip, and at mid-span. A generic low cycle fatigue life prediction model is used for these evaluations. Even though the probabilistic design process uses independent random numbers to simulate the variation, in reality, heat transfer coefficients at points located closely together should be correlated. For this reason, an autocorrelation function is implemented. By changing the value of this function the strength of the correlation of iv neighboring internal heat transfer coefficients to each other over a certain distance can be controlled. In order to test the effect that this correlation strength has on the low cycle fatigue life calculation, low and high values are chosen and analyzed. The magnitude of the prescribed uncertainty range of the internal heat transfer coefficient variation is varied to further study the effects on life. Investigated values include 5%, 10% and 20% for the straight ribbed passages and 10%, 20%, and 40% for both the tip and hub turns. As expected there is a significant dependence of low cycle fatigue life to the variation in internal heat transfer coefficients. For the 20/40% case, variations in life as high as 50-60% are recorded, furthermore a trend is observed showing that as the magnitude of the uncertainty range of internal heat transfer coefficients narrows so does the range of the low cycle fatigue life uncertainty.