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”.

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.

Ionic electroactive polymer (IEAP) transducers are a class of smart structures based on polymers that can be designed as soft actuators or sensors. IEAP actuators exhibit a high mechanical response to an external electrical stimulus. Conversely, they produce electrical signals when subjected to mechanical force. IEAP transducers are mainly composed of four different components: The ionomeric membrane (usually Nafion) is an ion permeable polymer that acts as the backbone of the transducer. Two conductive network composite (CNC) layer on both sides of the ionomeric membrane that enhance the surface conductivity and serve as an extra reservoir to the electrolytes. The electrolytes, (usually ionic liquids (IL)), which provides the mobile ions. And two outer electrodes on both sides of the transducer to either provide a distributed applied potential across the actuators (usually gold leaves) or to collect the generated signals from the sensors (usually copper electrodes). Any variation in any of these components or the operating conditions will directly affect the performance of the IEAP transduces. In this dissertation, we studied some of the parameters dominating the performance of the IEAP transducers by varying some of the transducers components or the transducers operating conditions in order to enhance their performance.

The first study was conducted to understand the influence of ionic liquid concentration on the electromechanical performance of IEAP actuators. The IL weight percentage (wt%) was varied from 10% to 30% and both the electromechanical (induced strain) and the electrochemical (the current flow across the actuators) were studied. The results from this study showed an enhanced electrochemical performance (current flow is higher for higher IL wt%) and a maximum electromechanical strain of approximately 1.4% at 22 wt% IL content. A lower induced strain was noticed for IL wt% lower or higher than 22%.

The second study was to investigate the effect of changing the morphology of the CNC on the sensing performance of IEAP stress sensors. In this study, small salt molecules were added to the CNC layers. Salt molecules directly affected the morphology of the CNC layers resulting in a thicker, more porous, and high conductive CNCs. As a result, the ionic conductivity increased through the CNC layers and sensing performance was enhanced significantly.

In the third study, a non-linear angular deformation (limb-like motion) was achieved by varying the CNC layers of the IEAP actuators by adding some conjugated polymers (CP) patterns during the fabrication of the actuators. It was found that the segments with the CP layers will only expand and never contract during the actuation process. Depending on the direction of motion and the location of the CP layers, different actuation shapes such as square or triangular shapes were achieved rather than the typical circular bending.

In the fourth study, the influence of temperature on the electromechanical properties of the IEAP actuators was examined. In this study, both electromechanical and electrochemical studies were conducted for actuators that were operated at temperatures ranging from 25 à °C to 90 à °C. The electromechanical results showed a lower cationic curvature with increasing temperature up to 70 à °C. On the other hand, a maximum anionic curvature was achieved at 50 à °C with a sudden decrease after 50 à °C. Actuators started to lose functionality and showed unpredictable performance at temperatures higher than 70 à °C. Electrochemically, an enhancement of the ionic conductivity was resulted from increasing temperature up to 80 à °C. A sudden increase in current flow was recorded at 90 à °C indicating a shorted circuit and actuator failure.

Finally, in the fifth study, protons in Nafion membranes were exchanged with other counterions of different Van der Waals volumes. The ionic conductivity was measured for IEAP membranes with different counterions at different temperatures. The results showed higher ionic conductivities across membranes with larger Van der Waals volume counterions and higher temperatures. A different ionic conductivity behavior was also noticed for temperatures ranging from 30 à ºC to 55 à ºC than temperatures between 55 à ºC and 70 à ºC after fitting the data with the Arrhenius conductivity equation.

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.

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.

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.

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.