The turbulent flow through a marine propulsor was experimentally modeled using a large cascade configuration with six 33 cm chord flat plates spanning the entire height of the test section in the Virginia Tech Stability Wind Tunnel. Three-component hot-wire velocity measurements were obtained ahead, throughout and behind both an unstaggered and a 35º staggered cascade configuration with blade spacing and onset turbulence integral scales on the order of the chord. This provided a much needed data-set of much larger Taylor Reynolds number than previous related studies and allowed a thorough investigation of the blade-blocking effects of the cascade on the incident turbulent field. In order to generate the large scale turbulence needed for this study, a mechanically rotating "active" grid design was adopted and placed in the contraction of the wind tunnel at a streamwise location sufficient to cancel out the relatively large inherent low frequency anisotropy associated with this type of grid. The resulting turbulent flow is one of the largest Reynolds number (Reλ  1000) homogeneous near-isotropic turbulent flows ever created in a wind tunnel, and provided the opportunity to investigate Reynolds number effects on turbulence parameters, especially relating to inertial range dynamics. Key findings include 1) that the extent of local isotropy is solely determined by the turbulence generator and the size of the wind-tunnel that houses it; and 2) that the turbulence generator operating conditions affect the shape of the equilibrium range at fixed Taylor Reynolds number. The latter finding suggests that grid turbulence is not necessarily self-similar at a given Reynolds number independent of how it was generated. The experimental blade-blocking data was compared to linear cascade theory and showed good qualitative agreement, especially for wavenumbers above the region of influence of the wind tunnel and turbulence generator effects. As predicted, the turbulence is permanently modified by the presence of the cascade after which it remains invariant for a significant downstream distance outside the thin viscous regions. The obtained results support the claim that Rapid Distortion Theory (RDT) is capable of providing reasonable estimates of the flow behind the cascade even though the experimental conditions lie far outside the predicted region of validity. / Ph. D.

This dissertation presents measurements of the far-field noise associated with the interaction of grid-generated turbulence with a series of airfoils of various chord lengths, thicknesses, and camber. The radiated noise was measured for a number of angles of attack for each airfoil to determine the effects of angle of attack on the leading edge noise. Measurements are compared with numerous theories to determine the mechanism driving the production of leading edge noise. Calculations were also made using a boundary element method to determine the effects of airfoil shape on the unsteady loading spectrum on the different airfoils to attempt to explain the far-field noise. Measurements of the unsteady surface pressure on a single airfoil were made for a number of angles of attack to determine the effects of wind tunnel interference corrections on the unsteady surface pressure. These measurements were compared with those of Mish (2003) to determine the effects of the interference correction. An attempt was also made to correlate the unsteady loading on the airfoil with the far-field noise. The airfoils studied were a 0.203-m chord NACA 0012, a 0.61-m chord NACA 0015, a 0.914-m chord NACA 0012, a 0.914-m chord DU96, and a 0.914-m chord S831. All airfoils spanned the entire 1.83-m height of the test section. Measurements were made using the Virginia Tech Stability Wind Tunnel in its acoustic configuration with an anechoic test section with side walls made of stretched Kevlar fabric to reduce aerodynamic interference. Measurements were made in grid-generated turbulence with an integral length scale of 8.2-cm and a turbulence intensity of 3.9%. Far-field noise measurements were made at Mach numbers of 0.087 and 0.117 with various configurations of up to 4 Bruel and Kjaer microphones mounted at an observer angle of 90° measured from the wind tunnel axis. Unsteady surface pressure measurements were made on the NACA 0015 airfoil immersed in the same grid generated turbulence used in the far-field noise study. An array of microphones mounted subsurface along the airfoil chord and a spanwise row was used to measure the unsteady surface pressure. These measurements were made at angles of attack from 0 through 16° in 2° increments. Far-field noise measurements of the leading edge noise show a consistent angle of attack effect. The radiated noise increases as the angle of attack is increased over the frequency range. These effects are small for large integral scale to airfoil chord ratios. The larger airfoils have been shown to generate significantly less leading edge noise at high frequencies, but this effect does not appear to be solely dependent upon the leading edge radius. The leading edge noise can be predicted with accuracy using the method of Glegg et al. (2008). Unsteady surface pressure measurements have been shown to be largely independent of the wind tunnel interference correction as shown by comparison with Mish (2008). The same low frequency reduction described by Mish was seen for an interference correction that was nearly 30% larger. The unsteady sectional lift spectra have been shown to be related to the far-field noise spectra by a factor close to the dipole efficiency factor; however, no correlation could be found between the instantaneous unsteady surface pressure and the radiated noise. The spanwise averaged unsteady pressure difference spectra have been shown to be related to the far-field noise spectra by the dipole efficiency factor. / Ph. D.

The technical feasibility of hypersonic flight (i.e., re-entry, hypersonic flight vehicles, cruise missiles, etc.) hinges on our ability to understand, predict, and control the transport of turbulence in the presence of non-equilibrium effects. A theoretical analysis of the governing equations suggests a mechanism by which fluctuations in internal energy are coupled to the transport of turbulence. Numerical studies of these flows have been conducted, but limited computational power results in reduced fidelity. Experimental studies are exceedingly rare and, consequently, experimental data available to build and evaluate turbulence models is nearly non-existent. The Decaying Mesh Turbulence (DMT) facility was designed and constructed to generate a fundamental decaying mesh turbulent flow field with passive grids. Vibrational non-equilibrium was achieved via a capacitively-coupled radio-frequency (RF) plasma discharge which required an operating pressure of 30 Torr. The flow velocity was 30 m/s. Data was recorded with each grid at multiple plasma powers (Off, 150 W, and 300 W). Over two terabytes of highly resolved (3,450 image pairs) two-dimensional particle image velocimetry (PIV) was acquired and archived. Temperature measurements were carried out using coherent anti-Stokes Raman spectroscopy (CARS). The primary objective of this study was to answer the fundamental scientific question: "Does thermal non-equilibrium alter the decay rate of turbulence?" The results of this study show that the answer is "Yes." The results demonstrate a clear coupling between thermal non-equilibrium and turbulence transport. The trends observed agree with those expected based on an analysis of the Reynolds stress transport equations, which provides confidence in transport equation-based modeling. A non-trivial reduction (~30%) in the decay rate downstream of the 300 W plasma discharge was observed. The data also show that the decay of TKE downstream of the plasma discharge was delayed (~20% downstream shift). In addition, the thermal non-equilbrium was observed to have no effect on the transverse stress. This suggests that, for this flow, the energy dilatation terms are small and unaffected by the plasma discharge, which simplifies modeling.

"The present study utilizes the ultrasonic travel-time technique to diagnose grid-generated turbulence. The statistics of the travel-time variations of ultrasonic wave propagation along a path are used to determine some metrics of the turbulence. The motivation for this work stems from the observation of substantial delta-t variation in ultrasonic measuring devices like flow meters and circulation meters. Typically, averaging can be used to extract mean values from such time series. The corollary is that the fluctuations contain information about the turbulence. Experimental data were obtained for ultrasonic wave propagation downstream of a heated grid in a wind tunnel. Such grid-generated turbulence is well characterized and features a mean flow with superimposed velocity and temperature fluctuations. The ultrasonic path could be perpendicular or oblique to the mean flow direction. Path lengths were of the order of 0.3 m and the transducers were of 100 kHz working frequency. The data acquisition and control system featured a very high-speed analog to digital conversion card that enabled excellent resolution of ultrasonic signals. Experimental data for the travel-time variance were validated using ray acoustic theory along with the Kolmogorov “2/3” law. It is demonstrated that the ultrasonic technique, together with theoretical models, provides a basis for turbulent flow diagnostics. As a result, the structure constant appearing in the Kolmogorov “2/3” law is determined based on the experimental data. The effect of turbulence on acoustic waves, in terms of the travel time, was studied for various mean velocities and for different angular orientations of the acoustic waves with respect to the mean flow. Average travel time in the presence of turbulence was shorter then in the undisturbed media. The effect of the time shift between the travel times in turbulent and undisturbed media is associated with Fermat’s principle. The travel time and log-amplitude variance of acoustic waves were investigated as functions of travel distance and mean velocity over a range of Reynolds number varying from 4000 to 20000. Experimental data are interpreted using classical ray acoustic approach and the parabolic acoustic equation approach together with the perturbation method. It was experimentally demonstrated that there is a strong dependence of the travel time on the mean velocity even in the case where the propagation of acoustic waves is perpendicular to the mean velocity. The effect of thermal fluctuations, which result in fluctuations of sound speed, was studied for two temperatures of the grid: (no grid heating) and . A semi analytical acoustic propagation model that allows determination of the spacial correlation functions of flow field is developed based on the classical flow meter equation and statistics of the travel time of acoustic waves traveling through the velocity and the thermal turbulence. The basic flow meter equation is reconsidered in order to take into account sound speed fluctuations and turbulent velocity. The resulting equation is written in terms of correlation functions of travel time, sound speed fluctuation and turbulent velocity fluctuations. Experimentally measured travel time statistics data with and without grid heating are approximated by Gaussian function and used to solve the integral flow meter equation in terms of correlation functions analytically."

An isolated wing-tip vortex from a square-tipped NACA 0012 wing at an angle of attack of 5 degrees was studied in a water tunnel at a chord based Reynolds number of approximately 24000. Measurements were taken using stereo particle image velocimetry at three measurement planes downstream of the wing under each of three freestream turbulence conditions. The amplitude of wandering of the vortex axis increased with increasing distance downstream of the wing and with increasing freestream turbulence intensity. The magnitude of the peak azimuthal velocity decreased with increasing distance from the wing as well as with increases in the freestream turbulence intensity. The streamwise velocity in the vortex core was less than the freestream velocity in all cases. Time resolved histories of the instantaneous waveform shape and location of the vortex axis were determined from sequences of images of fluorescent dye released from the wing.

An isolated wing-tip vortex from a square-tipped NACA 0012 wing at an angle of attack of 5 degrees was studied in a water tunnel at a chord based Reynolds number of approximately 24000. Measurements were taken using stereo particle image velocimetry at three measurement planes downstream of the wing under each of three freestream turbulence conditions. The amplitude of wandering of the vortex axis increased with increasing distance downstream of the wing and with increasing freestream turbulence intensity. The magnitude of the peak azimuthal velocity decreased with increasing distance from the wing as well as with increases in the freestream turbulence intensity. The streamwise velocity in the vortex core was less than the freestream velocity in all cases. Time resolved histories of the instantaneous waveform shape and location of the vortex axis were determined from sequences of images of fluorescent dye released from the wing.