The mutual instability of a trailing vortex pair has been studied in the Department's large wind tunnel. The vortices were visualized using helium filled soap bubbles and the cores probed with a hot wire anemometer. Measurements were made to permit calculation of the wing lift, the circulation of the trailing vortices, the vortex separation, the diameter of the vortex cores and the wavelength and plane of oscillation of the disturbed vortices. The results show that the linear theories of Crow and Parks closely predict the initial growth of the instability. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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.

No description available.

No description available.

The need for more efficient and environmentally sustainable aircraft has been a rapidly increasing topic for research and development over the last few decades. Within this area of research, boundary layer ingestion (BLI) concepts have been developed which integrates the airframe and propulsion system of an aircraft. In turn, BLI increases the fuel efficiency and decreases emissions by reducing the overall drag and reenergizing the aircraft wake. However, the boundary layer flow of an airframe or duct can impose undesired flow conditions, such as swirl and pressure distortions, at the inlet of a jet engine. Therefore, efficient research and testing capabilities are essential to advance the development of these integrated systems. The StreamVane swirl distortion generator was developed by Virginia Tech to provide cost and time efficient ground testing methods for BLI research. StreamVanes are constructed of unique vane packs that are specifically tailored to generate a desired swirl distortion profile. To maximize efficiency, StreamVanes are additive manufactured which cause geometry limitations to the overall vane design. Due to these restrictions, as well as the complexity of the vane pack, unwanted dynamic responses and unsteady flows can be generated. In order to predict both of these phenomena before testing, two different computational methodologies were developed and investigated on a StreamVane and its airfoil parameters. First, a one-way fluid-structure interaction methodology was developed to predict flutter mconditions of the vanes within StreamVanes. The presented methodology includes steady and unsteady computational fluid dynamics (CFD) as well as linear structural and modal finite element analysis (FEA) simulations. A simplified StreamVane model was designed as a testcase for the methodology, and it was found that two unique vane shapes did not undergo flutter conditions at three different operating points. The results provided a linear analysis method to compute the aerodynamic damping, which gave insight on how different vane shapes respond dynamically. Secondly, a parameter study was conducted to predict the vortex shedding from the modified NACA 63-series airfoil profile used within StreamVane design. The effects of the airfoil turning angle and trailing edge thickness on the vortex shedding frequency were computationally predicted using the unsteady Reynolds averaged Navier-Stokes equations (URANS) and shear stress transport (SST) turbulence model. In turn, the shedding frequencies for each parameter were recorded, and more intuition was gained on the TE flow field in correspondence to different airfoil specifications. Overall, the two sets of methodologies and results can be used to efficiently reduce failure uncertainties in future StreamVane designs. / Master of Science / The need for more efficient and environmentally sustainable aircraft has been a rapidly increasing topic for research and development over the last few decades. Within this area of research, boundary layer ingestion (BLI) concepts have been developed to advance the fuel efficiency in future aircraft designs. However, unlike traditional tube and wing aircraft, BLI produces nonuniform flow at the engine inlet, reducing the performance and durability of jet engine components. Therefore, more efficient research and testing capabilities are essential to advance the development of BLI aircraft. The StreamVane swirl distortion generator was developed by Virginia Tech to provide cost and time efficient ground testing methods for BLI research. These devices can be secured upstream of a test engine, and their complex vane pack can produce the same nonuniform flow found at the inlet of BLI aircraft engines. To further increase efficiency, StreamVanes are additive manufactured which causes geometry limitations to the overall vane design. Due to these restrictions, as well as the complexity of the vane pack, unwanted dynamic responses and unsteady flows can be generated. In order to predict both of these phenomena before testing, two different computational methodologies were developed and investigated on a StreamVane and its airfoil parameters. The first methodology was developed to compute the fluid dynamics and structural response of a simplified StreamVane model at different operating conditions. The results provided insight on how different vanes react dynamically to the surrounding flow field. The second methodology included a parameter study to predict the frequencies generated from the StreamVane airfoils. With these frequencies, more intuition was gained on how the overall fluid-structure system would behave. Overall, both methodologies and results can be used to efficiently reduce failure uncertainties in future StreamVane designs.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: Vortex; unsteady flow; circulation; three-dimensional flow; aerodynamics; instantaneous lift. Includes bibliographical references (p. 182-188).

No description available.

No description available.

No description available.