Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / M.S.

Thesis (M.S.)--California Polytechnic State University, 2008. / Mode of access: Internet. Title from PDF title page; viewed on March 17, 2009. Major professor: David D. Marshall. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree of Master of Science in Aerospace Engineering." "June 2008." Includes bibliographical references (p. 126-127). Also available on microfiche.

Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2007. / Dimitri N. Mavris, Committee Chair ; Lakshmi N. Sankar, Committee Member ; Daniel P. Schrage, Committee Member ; Robert J. Englar, Committee Member ; Robert C. Michelson, Committee Member.

A continuous vorticity panel method is developed and utilized to predict the steady aerodynamic loads on lifting surfaces having sharp-edge separation. Triangular and semi-infinite panels with linearly varying vorticity are used. The velocity field generated by an individual element is obtained in closed form. A concentrated core of vorticity is employed to simulate the leading-edge-vortex core and its feeding sheet. An optimization scheme is constructed for finding the vorticity at the nodes of the elements. The method is not restricted by aspect ratios, angles of attack, planforms, or camber. The numerical results are in good agreement with the experimental data for both rectangular and delta wings for incompressible flows. / Ph. D.

An explicit algebraic Reynolds stress model (EARSM) based ona pressure strain rate model including terms tensoriallynonlinear in the mean velocity gradients is developed in orderto improve predictions for .ows with strong curvature and/orrotation. This work has been carried out in the context of acollaborative international project on high-lift aerodynamics.For 2D mean .ows the nonlinear terms can easily be accountedfor in the model formulation. This is not the case for 3D mean.ows and approximations making the 2D and 3D mean .owformulations consistent are suggested. The proposed EARSM, theparent-EARSM and the corresponding di.erential Reynolds stressmodels (DRSM) are tested for spanwise rotating channel .ow andaxially rotating pipe .ow. The model predictions are comparedto experimental and DNS data. The nonlinear extensions areshown to have a signi.cant e.ect on the .ow predictions,somewhat less pronounced for the DRSM though. The turbulentdi.usion modelling in the EARSM computations is important forthe rotating pipe. It is shown that by using a Daly and Harlowdi.usion model, turbulence levels in good agreement withexperiments and DRSM can be achieved. However, by using asimpler e.ective eddy viscosity based di.usion model theturbulence kinetic energy levels are drastically overpredicted.Finally the proposed EARSM is tested on a standard high-liftcon.guration. The EARSM predictions are compared withexperiments and the predictions made by the standard K - ωtwo-equation model. Descriptors:Turbulence model, nonlinear modelling,streamline curvature, high-lift aerodynamics.

The word hysteresis is derived from a Greek word meaning "to lag 'behind". As specifically applied to fluid flow around bodies with transient angles of attack in and near the stall region, "aerodynamic hysteresis" is used to describe the effect of delay in boundary layer separation and reattachment upon the lift, drag and pitching moment. Experimental work done on airfoils by H. Studer showed that for increasing angles of attack flow "separation is delayed to an angle of attack appreciably greater than that for a stationary airfoil. On the return movement, re-establishment of a smooth flow is also delayed." [1]* The result is that under transient conditions "more than one value of flow coefficient (and thus lift, drag and pitching moment) can be obtained for a single angle of attack. . ., depending upon the direction in which the particular angle of attack is approached." [2]

No description available.

This dissertation investigates spanwise periodic shear flow past two-dimensional bodies. The flow is assumed to be inviscid and incompressible. Using singular perturbation techniques, the solution is developed for ε = L/ℓ ≪ 1, where L represents body cross-sectional size, and ℓ the period of the oncoming flow U(z). The singular perturbation analysis involves three regions: the inner, wake and outer regions. The leading order solutions are developed in all regions, and in the inner region higher order terms are obtained. In the inner region near the body, the primary flow (U₀, V₀, P₀) corresponds to potential flow past the body with a local free stream value of U(z). The spanwise variation in U(z) produces a weak O(ε) secondary flow W₁ in the spanwise direction. As the vortex lines of the upstream flow are convected downstream, they wrap around the body, producing significant streamwise vorticity in a wake region of thickness O(L) directly behind the body. This streamwise vorticity induces a net volume flux into the wake. In the outer region far from the body, a nonlifting body appears as a distribution of three-dimensional dipoles, and the wake appears as a sheet of mass sinks. Both singularity structures must be included in describing the leading outer flow. For lifting bodies, the body appears as a lifting line, and the wake appears as a sheet of shed vorticity. The trailing vorticity is found to be equal to the spanwise derivative of the product of the circulation and the oncoming flow. For lifting bodies the first higher order correction to the inner flow is the response of the body to the downwash produced by the trailing vorticity. At large distances from the body, the flow takes on remarkably simple form.

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 (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by Graham Taber Skinner. / M.S.