Thesis (PH. D.)--Michigan State University. Mechanical Engineering, 2008. / Title from PDF t.p. (viewed on Sept. 8, 2009) Includes bibliographical references (p. 104-108). Also issued in print.

Previously, the concept of the tolerant wind tunnel, developed in the Department of Mechanical Engineering, U. B. C., was tested only for stationary models. In the present study, the concept is investigated for unsteady airfoil motion. The new wind tunnel test section, using the opposite effects of solid and open boundaries, is a new approach to reduce wall blockage effects. Consisting of vertical airfoil slats uniformly spaced on both side walls in the test section, it is designed to produce a nearly free-air test environment for the test model, which leads to negligible or small corrections to the experimental results. The performance of this wind tunnel for unsteady model testing is examined experimentally with a two-dimensional NACA 0015 airfoil in a simple plunging sinusoidal motion. The airfoil is mounted vertically in the center plane of the test section between solid ceiling and floor. An oscillating table is designed to give the airfoil an accurate plunging sinusoidal motion. A full range of open area ratio is tested by varying the number of slats mounted inside the side walls. Pressure distribution along the airfoil surface and displacement of the airfoil are measured as functions of time by a data acquisition system designed for this research. Lift and moment are obtained by integration of the pressure distribution at every time increment. Using a numerical model based on the singularity distribution method, the free air case results for a NACA 0015 airfoil in the same unsteady motion are obtained. Comparison with the linear theory results by Sears¹ are discussed. Comparing with the numerical and the linear theory results, the experimental investigation shows that the new test section produces low-correction data. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

No description available.

No description available.

Ph. D.

A two-dimensional, inviscid, incompressible procedure is presented for predicting the unsteady lift on turbomachinery blades caused by the upstream potential disturbance of downstream flow obstructions. The method is applied to a particular geometry which consists of a rotor, a downstream stator, and downstream struts which support the engine casing. Using the Douglas-Neumann singularity superposition computer program to model the downstream flow obstructions, classical equations of thin airfoil theory are then employed, to compute the unsteady lift on the upstream rotor blades. Very good agreement between the Douglas-Neumann program and experimental measurements was obtained for the downstream stator-strut flow field. The calculations for the unsteady lift due to the struts were in good agreement with the experiments in showing that the unsteady lift due to the struts decays exponentially with increased axial separation of the rotor and the struts. However, the calculations for the unsteady lift due to the stator were two orders of magnitude smaller than that measured in experiments. This is attributed to the strong viscous interaction between the rotor and stator blade rows. / M.S.

The largely unstudied extension of ultrasonic circulation measurement techniques (UCMT) to determine instantaneous lift in unsteady and three-dimensional flows has been addressed in this work. A combined analytical-numerical-experimental approach was undertaken with the goal of developing methods to properly convert the measurable time-dependent bound circulation to instantaneous lift force in unsteady flows. The measurement of mean sectional lift distribution along structure spans in three-dimensional flows was also studied. An unsteady correction method for thin airfoils was developed analytically and validated numerically (with finite element solutions) to properly convert bound circulation to instantaneous lift based on unsteady potential flow theory. Results show that the unsteady correction method can provide increased accuracy for unsteady lift prediction over the Kutta-Joukowski method used in previous unsteady flow studies. The unsteady correction model generally should be included for instantaneous lift prediction as long as the bound circulation is time-dependent. Using the same framework, we also studied determination of instantaneous lift forces on stationary bluff bodies (circular cylinders) at low Reynolds number (Re=100). Various force models, including an approximate vortex force model, were studied. A new unsteady model, similar to that developed for the thin airfoils, using instantaneous bound circulation values, was proposed. Another important issue studied in this thesis is the effect of acoustic path sensitivity on bound circulation determination, which we found to be crucial for accurately predicting the instantaneous lift in both unsteady flat plate and cylinder flows. Proper path selection should take into account the location of boundary layers, attached and shed vortices. These findings will be useful in future experimental design of UCMT, PIV and LDV methods. Finally, we used the UCMT method to experimentally study the mean spatial lift distribution along structures. Low Reynolds number low aspect ratio (AR) wings that have application in micro-aerial-vehicles (MAV) were studied. The spanwise circulation (lift) distribution along the MAV wings exhibits a peak (maximum), and deviates from predictions of Prandtl's lifting line theory. Although only 'linear' lift (due to bound circulation) was measured, comparison with force balance results showed that reasonable integrated lift values on low Re, low AR wings can be obtained using UCMT.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO / Includes bibliographical references. / by Saeed Farokhi. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Michael E. McClurken. / Ph.D.

Unsteady flow separation represents a highly complex and important area of study within fluid mechanics. The extent of separation and specific time scales over which it occurs are not fully understood and has significant consequences in numerous industrial applications such as helicopters, jet engines, hydroelectric turbines and wind turbines. A direct consequence of unsteady separation is the erratic movement of the separation point which causes highly dynamic and unpredictable loads on an airfoil. Current computational models underestimate the aerodynamic loads due to the inaccurate prediction of the emergence and severity of unsteady flow separation especially in response to a sudden change in the effective angle of attack. To capture the complex flow phenomena over wind turbine blades during stall development, a scaled three-dimensional non-rotating blade model is designed to be dynamically similar to a rotating full-scale NREL 5MW wind turbine blade. A time-resolved particle image velocimetry (PIV) investigation of flow behavior during the stall cycle examines the processes of stall development and flow reattachment. The flow fields are examined through the application of Eulerian techniques such as proper orthogonal decomposition and empirical mode decomposition to capture unsteady separation characteristics within the flow field. Then, for a higher order description, coherent structures such as vortices and material lines are resolved to fully characterize the flow during a full pitching cycle in a Lagrangian framework. The Eulerian and Lagrangian methods described in the present analysis is extended to investigate the spanwise characteristics within the root section of a three dimensional airfoil. Furthermore, statistical information of the separation point is pursued along four spanwise positions during two cases of unsteady separation. The results of the study describe a critical role of surface vorticity accumulation in unsteady separation and reattachment. Evaluation of the unsteady characteristics of the shear layer reveal evidence that the build-up and shedding of surface vorticity directly influence the dynamic changes in separation point. The quantitative characterization of surface vorticity and shear layer stability enables improved aerodynamic design, but also has broader implications on the larger discipline of unsteady fluid dynamics.