A scheme based on the Boundary Element Method (BEM) for solving the problem of steady flow of an incompressible viscous fluid is presented in this thesis. The problem is governed by both Navier-Stokes (N-S) equations and the continuity equation. The fundamental solution of the two-dimensional N-S is derived, and the partial differential equations are converted to an integral equation;The computer code is flexible enough to handle a variety of boundary and domain elements with different degrees of interpolation polynomial. Boundary and domain integrals over corresponding elements are evaluated analytically. The Newton Raphson iteration scheme accompanied by a relaxation factor is used to solve the nonlinear equations. The code includes a post processor that calculates the velocity components at any point inside the domain;The scheme has been applied to three test problems. The first concerns Couette flow, which has been used as a test case for testing the rate of convergence and accuracy. The second and the third concern the driven cavity and the flow in a stepped channel, respectively;In the integral equation formulation, the primary unknowns are tractions on the domain boundary and velocities in the interior. Because the shear stress, drag, and lift can be simply computed from the values of tractions along the boundary, such a formulation is markedly superior to either the finite-difference or the finite-element formulation. In customary pressure-velocity or streamfunction-vorticity formulations, employed in the finite-difference or finite-element methods, calculation of stress, drag, and lift involves extensive postprocessing.

This work has two primary parts: (1) an exhaustive literature review highlighting the need and the direction to study broadband noise generation from the fan stage of a modern high bypass ratio turbofan engine, and (2) a benchmark study of noise generation by the flow over a rod and an airfoil in tandem arrangement. The literature review highlights that not all the experimental data has been consistently explained with the theory and thus these gaps are required to be filled in to improve the fan noise prediction during the design phases. The benchmark case provides flow conditions where the upstream located circular rod sheds periodic vortices and creates turbulence which interacts with downstream located symmetric airfoil at zero angle of attack. This interaction produces noise which radiates to farfield. The periodic shedding and the resulting turbulence provides energy to the tonal and broadband components of the total noise. This test case is used to validate a new approach to predict noise in farfield which uses incompressible flow solver, pimpleFoam (part of OpenFOAM), along with Amiet's theory.

Downstream turbines in a wind farm often operate under the influence of wakes from upstream turbines. Aerodynamic losses and aeromechanical issues (stochastic loads) associated with such wake-turbine interactions have been investigated before. However, the role such interactions play in the generation of aerodynamic noise has not been evaluated. This paper presents a two-step approach for predicting noise due to wake-turbine interaction. The first step involves an aerodynamic analysis of a wind farm using large eddy simulations. Time accurate data and turbulence statistics in the turbine wakes are obtained from this simulation just ahead of the downstream wind turbines. The second step uses the turbulence information with aeroacoustic models to predict radiated noise in the far field. Simulation results of two simplified model problems corresponding to these two steps are presented in this paper.

Pitot probes are one of the most important components of an airplane, directly responsible for the flight safety and secure decisions of pilots by providing crucial airspeed and altitude data. They are constantly at risk of performance deterioration due to ice accretion that can block the stagnation port, thereby, providing incorrect readings to the pilot that can lead to fatal accidents if not treated immediately. By leveraging the unique Icing Research Tunnel at Iowa State University (i.e., ISU-IRT) a series of experimental studies are conducted to investigate the dynamic ice accretion process over the surface of a commonly-used aircraft pitot probe and to evaluate the effectiveness of various anti-/de-icing methods for Pitot probe icing mitigation. During the experiments, in addition to using a high-resolution imaging system to record the dynamic ice accretion and anti-/de-icing processes over the surface of the Pitot probe under different icing test conditions, a high-speed Infrared (IR) thermal imaging system is also used to map the corresponding surface temperature distributions on the Pitot probe in order to characterize the unsteady heat transfer process associated with the ice accretion and anti-/de-icing process. In addition to performing a parametric study to evaluate the performance of a conventional thermal-based icing protection system embedded inside the Pitot-probe as a function of the electric power input for the anti-/de-icing operation, a novel hybrid icing protection strategy is proposed that combines the electric heating with a bio-inspired superhydrophobic (SHS) coating to coat the Pitot probe in order to minimize the power consumption for the anti-/de-icing operation. In comparison to that required by the conventional thermal-based system to heat up the Pitot probe brutally for icing protection, the proposed hybrid strategy is found to be able to achieve completely ice free conditions over the entire surface of the Pitot probe with only about 35% of the required power input (i.e., up to 65% power consumption) for the anti-/de-icing operation.

This paper was developed from the remarks delivered to honor Don Thompson by the banquet speakers at the 40th QNDE meeting, July 2013. Don died peacefully at his home just days later on July 29th after a two year battle with cancer. “Don was a tenacious fighter for what he believed in, and his vision and perseverance did much to establish NDE in both the US and wider global R&D community. He will be greatly missed by his many friends and colleagues in the NDE community”.

Noise produced by aerodynamic interaction between a circular cylinder (rod) and an airfoil in a tandem arrangement is investigated numerically using incompressible large eddy simulations. Quasi-periodic shedding from the rod and the resulting wake impinges on the airfoil to produce unsteady loads on the two geometries. These unsteady loads act as sources of aerodynamic sound and the sound radiates to the far-field with a dipole directivity. The airfoil is set at zero angle of attack for the simulations and the Reynolds number based on the rod diameter is Red = 48 K. Comparisons with experimental measurements are made for (a) mean and root mean square surface pressure on the rod, (b) profiles of mean and root mean square streamwise velocity in the rod wake, (c) velocity spectra in the near field, and (d) far-field pressure spectra. Curle’s acoustic analogy is used with the airfoil surface pressure data from the simulations to predict the far-field sound. An improved correction based on observed spanwise coherence is used to account for the difference in span lengths between the experiments and the simulations. Good agreement with data is observed for the near-field aerodynamics and the far-field sound predictions. The straight leading edge airfoil is then replaced with a test airfoil with a serrated leading edge geometry while maintaining the mean chord. This new configuration is also analyzed numerically and found to give a substantial reduction in the far-field noise spectra in the mid- to high-frequency range. Source diagnostics show that the serrations reduce unsteady loading on the airfoil, reduce coherence along the span, and increase spanwise phase variation, all of which contribute to noise reduction.

A new nonequilibrium turbulence closure model has been developed for computing wall bounded two-dimensional turbulent flows. This two-layer eddy viscosity model was motivated by the success of the Johnson-King model in separated flow regions. The influence of history effects are described by an ordinary differential equation developed from the turbulent kinetic energy equation. The performance of the present model has been evaluated by solving the flow around three airfoils using the Reynolds time-averaged Navier-Stokes equations. Excellent results were obtained for both attached and separated flows about the NACA 0012 airfoil, the RAE 2822 airfoil, and the Integrated Technology A 153W airfoil. Based on the comparison of the numerical solutions with the available experimental data, it is concluded that the new nonequilibrium turbulence model accurately captures the history effects of convection and diffusion on turbulence.

Aerodynamic noise produced by aerodynamic interaction between a cylinder (rod) and an airfoil in tandem arrangement is investigated using large eddy simulations. Wake from the rod convects with the flow, impinges of the airfoil to produce unsteady force which acts as a sound source. This rod-airfoil interaction problem is a model problem for noise generation due to inflow or upstream-generated turbulence interacting with a turbomachine bladerow or a wind turbine rotor. The OpenFoam and Charles (developed by Cascade Technologies) solvers are chosen to carry out the numerical simulations. The airfoil is set at zero angle of attack for the simulations. The flow conditions are specified by the Reynolds number (based on the rod diameter), Red = 48 K, and the flow Mach number, M = 0.2. Comparisons with measured data are made for (a) mean and root-mean-squared velocity profiles in the rod and airfoil wakes, (b) velocity spectra in the near field, and (c) far-field pressure spectra and directivity. Near-field flow data (on- and off-surface) is used with the Ffowcs Williams-Hawkings (FW-H) acoustic analogy as well as Amiet’s theory to predict far-field sound.

Simplified representations of the leading edge serrations in owl feathers are modeled numerically to investigate their effectiveness in reducing inflow turbulence noise. The rod wake-airfoil interaction problem is selected for this investigation. Two numerical methods utilizing compressible- and incompressible large eddy simulation techniques are used for the analyses. The methods are first validated against experimental results for the baseline airfoil (no serrations). Good agreement is observed between measurement and predictions for mean surface pressure, near-field velocity spectra, and far-field sound spectra. Two serrated leading edge blade designs are then analyzed for noise. The leading edge serrations are found to give a noise reduction of up to 5 decibels in the mid-to-high frequency range.