Jonathan W. Naughton

Bio: Jonathan W. Naughton is an academic researcher from University of Wyoming. The author has contributed to research in topics: Airfoil & Turbulence. The author has an hindex of 20, co-authored 162 publications receiving 1808 citations. Previous affiliations of Jonathan W. Naughton include Sandia National Laboratories & California Institute of Technology.

Grand challenges in the science of wind energy

Abstract: Harvested by advanced technical systems honed over decades of research and development, wind energy has become a mainstream energy resource. However, continued innovation is needed to realize the potential of wind to serve the global demand for clean energy. Here, we outline three interdependent, cross-disciplinary grand challenges underpinning this research endeavor. The first is the need for a deeper understanding of the physics of atmospheric flow in the critical zone of plant operation. The second involves science and engineering of the largest dynamic, rotating machines in the world. The third encompasses optimization and control of fleets of wind plants working synergistically within the electricity grid. Addressing these challenges could enable wind power to provide as much as half of our global electricity needs and perhaps beyond.

Multi-time-delay LSE-POD complementary approach applied to unsteady high-Reynolds-number near wake flow

Abstract: This investigation compared the application and accuracy of single- and multi-time-delay linear stochastic estimation-proper orthogonal decomposition (LSE-POD) methods in the temporal domain. These methods were considered for low-dimensional estimations of the dynamics of the energy-containing structures in a high Reynolds number flow. The near wake dynamics of a bluff body were used to demonstrate the robustness and accuracy of the investigated LSE-POD methods. Statistically independent two-dimensional particle image velocimetry (PIV) measurements were used to determine spatial POD modes, and time-resolved surface pressure measurements were used to determine LSE coefficients required for estimating the time-varying POD coefficients. A low-order, time-resolved reconstruction of the wake dynamics was accomplished using these estimated time-varying POD coefficients. The paper also provides details concerning the accuracy of the estimation using multi-time-delay LSE-POD. The results demonstrate that the multi-time LSE-POD technique is successful in capturing and reconstructing the important near wake dynamics. It is also shown that optimizing the time delays used for the estimations increases the accuracy of the reconstruction. As a result of its capabilities, the multi-time-delay implementation of the LSE-POD approach offers an alternate method for low-dimensional modeling that is attractive for real-time flow estimation.

Skin-friction measurements on the NASA hump model

Abstract: The skin-friction distribution on a wall-mounted hump model has been obtained using oil-film interferometry. This effort is part of a larger study to provide validation cases for simulations of unsteady flows. The challenges of using oil-film interferometry on this model, including model curvature and close camera proximity, are discussed. Skin-friction measurements are obtained over most of the hump model, including especially high-quality measurements in the separated and reattachment regions. These results highlight the method’s ability to capture a wide range of skin friction including measurements in reverse-flow and high-gradient regions. The wall skin-friction data are shown to complement other experimental data, and the use of independent skin-friction measurements for scaling in wall-bounded flows is emphasized. A comparison with results from several computational simulations of the same flow is presented. The comparison indicates that, for the most part, the computations accurately predict the skin-friction ahead of separation, but fail to predict the reattachment point correctly, and thus the comparison in the separated and recovery regions of the flow is poor. The ability of the skin-friction measurements to pinpoint regions where the computation performs poorly in the near-wall region is also presented. From these results, it is evident that independent skin-friction measurements should be a part of all validation experiments conducted in wall-bounded flows.

An experimental study of compressible turbulent mixing enhancement in swirling jets

Abstract: Compressible jets with various amounts of swirl and compressibility are investigated experimentally. The mixing-layer growth rate is obtained from time-averaged images of the mixing layer using the planar laser scattering (PLS) technique, and the swirl is quantified with laser Doppler velocimetry and intrusive probes. The results conclusively demonstrate that the addition of swirl to the jet increases entrainment by up to 60% compared to a corresponding non-swirling case. Instantaneous PLS images reveal modified turbulent structure in the mixing layer of the swirling-jet cases. In particular, analysis of these images indicates that both the spatial extent and amplitude of the largest turbulent fluctuations are increased when swirl is added. Based upon these results, a parameter β that correlates the observed growth-rate enhancement is proposed. This parameter is derived assuming that the streamwise vorticity, generated in the mixing layer by the addition of small amounts of swirl, causes additional turbulent mixing that increases the growth rate. When the available growth-rate data for swirling jets are plotted against this parameter, they collapse to a single curve with increased enhancement for higher values of β. This result implies that the degree of enhancement actually increases with compressibility, although the dimensional growth rates for the present compressible swirling-jet cases are still less than those of their incompressible counterparts.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

On Dynamic Mode Decomposition: Theory and Applications

Abstract: Originally introduced in the fluid mechanics community, dynamic mode decomposition (DMD) has emerged as a powerful tool for analyzing the dynamics of nonlinear systems. However, existing DMD theory deals primarily with sequential time series for which the measurement dimension is much larger than the number of measurements taken. We present a theoretical framework in which we define DMD as the eigendecomposition of an approximating linear operator. This generalizes DMD to a larger class of datasets, including nonsequential time series. We demonstrate the utility of this approach by presenting novel sampling strategies that increase computational efficiency and mitigate the effects of noise, respectively. We also introduce the concept of linear consistency, which helps explain the potential pitfalls of applying DMD to rank-deficient datasets, illustrating with examples. Such computations are not considered in the existing literature, but can be understood using our more general framework. In addition, we show that our theory strengthens the connections between DMD and Koopman operator theory. It also establishes connections between DMD and other techniques, including the eigensystem realization algorithm (ERA), a system identification method, and linear inverse modeling (LIM), a method from climate science. We show that under certain conditions, DMD is equivalent to LIM.

Review: Semiconductor Piezoresistance for Microsystems

Abstract: Piezoresistive sensors are among the earliest micromachined silicon devices. The need for smaller, less expensive, higher performance sensors helped drive early micromachining technology, a precursor to microsystems or microelectromechanical systems (MEMS). The effect of stress on doped silicon and germanium has been known since the work of Smith at Bell Laboratories in 1954. Since then, researchers have extensively reported on microscale, piezoresistive strain gauges, pressure sensors, accelerometers, and cantilever force/displacement sensors, including many commercially successful devices. In this paper, we review the history of piezoresistance, its physics and related fabrication techniques. We also discuss electrical noise in piezoresistors, device examples and design considerations, and alternative materials. This paper provides a comprehensive overview of integrated piezoresistor technology with an introduction to the physics of piezoresistivity, process and material selection and design guidance useful to researchers and device engineers.

Interpolation Method for Adapting Reduced-Order Models and Application to Aeroelasticity

Abstract: Reduced-order models are usually thought of as computationally inexpensive mathematical representations that offer the potential for near real-time analysis. Although most reduced-order models can operate in near real-time, their construction can be computationally expensive, as it requires accumulating a large number of system responses to input excitations. Furthermore, reduced-order models usually lack robustness with respect to parameter changes and therefore must often be rebuilt for each parameter variation. Together, these two issues underline the need for a fast and robust method for adapting precomputed reduced-order models to new sets of physical or modeling parameters. To this effect, this paper presents an interpolation method based on the Grassmann manifold and its tangent space at a point that is applicable to structural, aerodynamic, aeroelastic, and many other reduced-order models based on projection schemes. This method is illustrated here with the adaptation of computational-fluid-dynamics-based aeroelastic reduced-order models of complete fighter configurations to new values of the freestream Mach number. Good correlations with results obtained from direct reduced-order model reconstruction, high-fidelity nonlinear and linear simulations are reported, thereby highlighting the potential of the proposed reduced-order model adaptation method for near real-time aeroelastic predictions using precomputed reduced-order model databases.