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A design engineer has a desire to obtain the best possible design configuration producing the most desirable result. This is especially true in designs involving aerodynamics. This thesis presents a way to design the optimum airfoil for a non-lifting strut-like application. This is achieved by combining the governing laws of aerodynamics with appropriate numerical models to simulate an inputted steady flow regime. By using a robust yet simple parameterization method to represent airfoils and by implementing a genetic algorithm, optimization is achieved and occurs in a timely manner. Performing the optimization across a range of flow fields and for struts in different applications also allows some trends to be deduced, thus providing valuable knowledge to design engineers.

A large direct numerical simulation database spanning a wide range of Reynolds and Schmidt number is used to examine fundamental laws governing passive scalar mixing and turbulence structure. Efficient parallel algorithms have been developed to calculate quantities useful in examining the Kolmogorov small-scale phenomenology. These new algorithms are used to analyze data sets with Taylor scale Reynolds numbers as high as 650 with grid-spacing as small as the Kolmogrov length scale. Direct numerical simulation codes using pseudo-spectral methods typically use transpose based three-dimensional (3D) Fast Fourier Transforms (FFT). The ALLTOALL type routines to perform global transposes have a quadratic dependence on message size and typically show limited scaling at very large problem sizes. A hybrid MPI/OpenMP 3D FFT kernel has been developed that divides the work among the threads and schedules them in a pipelined fashion. All threads perform the communication, although not concurrently, with the aim of minimizing thread-idling time and increasing the overlap between communication and computation. The new algorithm is seen to reduce the communication time by as much as 30% at large core-counts, as compared to pure-MPI communication. Turbulent mixing is important in a wide range of fields ranging from combustion to cosmology. Schmidt numbers range from O(1) to O(0.01) in these applications. The Schmidt number dependence of the second-order scalar structure function and the applicability of the so-called Yaglomﾒs relation is examined in isotropic turbulence with a uniform mean scalar gradient. At the moderate Reynolds numbers currently achievable, the dynamics of strongly diffusive scalars is inherently different from moderately diffusive Schmidt numbers. Results at Schmidt number as low as 1/2048 show that the range of scales in the scalar field become quite narrow with the distribution of the small-scales approaching a Gaussian shape. A much weaker alignment between velocity gradients and principal strain rates and a strong departure from Yaglomﾒs relation have also been observed. Evaluation of different terms in the scalar structure function budget equation assuming statistical stationarity in time shows that with decreasing Schmidt number, the production and diffusion terms dominate at the intermediate scales possibly leading to non-universal behavior for the low-to-moderate Peclet number regime considered in this study. One of the few exact, non-trivial results in hydrodynamic theory is the so-called Kolmogorov 4/5th law. Agreement for the third order longitudinal structure function with the 4/5 plateau is used to measure the extent of the inertial range, both in experiments and simulations. Direct numerical simulation techniques to obtain the third order structure structure functions typically use component averaging, combined with time averaging over multiple eddy-turnover times. However, anisotropic large scale effects tend to limit the inertial range with significant variance in the components of the structure functions in the intermediate scale ranges along the Cartesian directions. The net result is that the asymptotic 4/5 plateau is not attained. Motivated by recent theoretical developments we present an efficient parallel algorithm to compute spherical averages in a periodic domain. The spherically averaged third-order structure function is shown to attain the K41 plateau in time-local fashion, which decreases the need for running direct numerical simulations for multiple eddy-turnover times. It is well known that the intermittent character of the energy dissipation rate leads to discrepancies between experiments and theory in calculating higher order moments of velocity increments. As a correction, the use of three-dimensional local averages has been proposed in the literature. Kolmogorov used the local 3D averaged dissipation rate to propose a refined similarity theory. An algorithm to calculate 3D local averages has been developed which is shown to scale well up to 32k cores. The algorithm, computes local averages over overlapping regions in space for a range of separation distances, resulting in N^3 samples of the locally averaged dissipation for each averaging length. In light of this new calculation, the refined similarity theory of Kolmogorov is examined using the 3D local averages at high Reynolds number and/or high resolution.

The purpose of this study is to quantify the effect of finescale turbulence on copepod behavior in order to shed light on the influence of turbulence on copepod distribution. Specifically, the study will examine the behavioral response of the marine copepod Acartia tonsa to a steady state Burgers' vortex intended to mimic the characteristics of a turbulent vortex (Jumars et al. [2009]) that a copepod is likely to encounter in the coastal zone. A laboratory apparatus was constructed to create a Burgers' vortex with size and strength consistent with turbulence vortices in the coastal zone (and relevant to the marine copepod species). The radius, circulation, and axial strain of the Burgers' vortex were specified to match typical dissipative vortices corresponding to two turbulence intensity levels. The levels are described by Webster et al. [2004] as Level 2 (ϵ = 0.009 cm²/s³) and Level 3 (ϵ = 0.096 cm²/s³), which span an apparent behavior transition in copepods [Yen et al., 2008]. Tomographic particle image velocimetry (Tomo - PIV) was performed to calibrate the device and verify that it produces the desired vortex characteristics, as well as to provide a three dimensional velocity vector field to compare with behavioral assays. The laboratory apparatus, dubbed the "Burgers' Vortex Apparatus", accurately reproduces the appropriate vortex characteristics of the Turbulence Level 2 and 3 vortex cartoons. Copepod behavioral assays were conducted with Acartia tonsa. When exposed to these vortices, Acartia tonsa did not exhibit a meaningful behavioral response to the Level 2 vortices, but drastically altered their swimming behavior in the presence of Level 3 vortices. In the presence of a Turbulence Level 3 vortex, Acartia tonsa increased relative swim speed, decreased turn frequency, increased the angle of alignment with the vortex axis, increased net-to-gross displacement ratio, and increased escape acceleration (relative to control). These alterations in swimming kinematics all served to move the animal away from the vortex core.

In this thesis, the effects of roughness on turbulent boundary layers are investigated by both the experimental and analytical methods. Two aspects of roughness are investigated, including the similarity between the smooth and rough turbulent boundary layers, and the characteristics of the flow over the step changes in roughness. Based on the data from the thesis of Akinlade (2005), the validity of three different kinds of outer scales is examined for the defect law in the context of smooth surface and three different types of rough surfaces. Furthermore, a mathematical relation is derived to further investigate the roughness effects. For the second topic, experiments were performed on a smooth-rough-smooth transition in a wind tunnel using a boundary layer Pitot tube. In addition, the growth rates of internal boundary layer thicknesses are determined using the method of Antonia and Luxton (1971, 1972), and the results are compared with the previous studies.

The second used a pre-heated flat plate in a transient wind tunnel to determine heat transfer rates with freestream turbulence generated by a number of parallel bar grids. Both liquid crystals and thin film gauges were used for heat-flux studies. A correlation has been derived that defines the heat transfer enhancement in terms of turbulence intensity and integral scale, as well as extending the conclusions of previous workers to apply at high intensities and with severe anisotropy.