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- All Subjects: Aerospace Engineering
Description
The current work aims to understand the influence of particles on scalar transport in particle-laden turbulent jets using point-particle direct numerical simulations (DNS). Such turbulence phenomena are observed in many applications, such as aircraft and rocket engines (e.g., engines operating in dusty environments and when close to the surface) and geophysical flows (sediment-laden rivers discharging nutrients into the oceans), etc.This thesis looks at systematically understanding the fundamental interplay between (1) fluid turbulence, (2) inertial particles, and (3) scalar transport. This work considers a temporal jet of Reynolds number of 5000 filled with the point-particles and the influence of Stokes number (St). Three Stokes numbers, St = 1, 7.5, and 20, were considered for the current work. The simulations were solved using the NGA solver, which solves the Navier-Stokes, advection-diffusion, and particle transport equations.
The statistical analysis of the mean and turbulence quantities, along with the Reynolds stresses, are estimated for the fluid and particle phases throughout the domain. The observations do not show a significant influence of St in the mean flow evolution of fluid, scalar, and particle phases. The scalar mixture fraction variance and the turbulent kinetic energy (TKE) increase slightly for the St = 1 case, compared to the particle-free and higher St cases, indicating that an optimal St exists for which the scalar variation increases. The current preliminary study establishes that the scalar variance is influenced by particles under the optimal particle St. Directions for future studies based on the current observations are presented.
ContributorsPaturu, Venkata Sai Sushant (Author) / Pathikonda, Gokul (Thesis advisor) / Kasbaoui, Mohamed Houssem (Committee member) / Kim, Jeonglae (Committee member) / Prabhakaran, Prasanth (Committee member) / Arizona State University (Publisher)
Created2023
Description
Direct Ink Deposition is a type of 3D printing that utilizes a nozzle to coat thin films onto substrates. Electrospray deposition is a subcategory of Direct Ink Deposition wherein a very strong electric field is applied between the nozzle exit and the substrate, which results in the precursor polymer ink to be sprayed onto the substrate in the form of micro- or nano-droplets. As of today, its applications are limited to producing small area polymer solar cells or for biomedical applications, particularly in laboratories, but in the future, with optimization of electrospray deposition, this method can be further expanded to 3D printing components that can be used in the aerospace, automotive, and other such large-scale industries. The objective of this research is to see how application of ultrasonic vibrations during, and post deposition affects the morphology, electrical conductivity, and the respective surface properties of the thin Poly(3,4 – Ethylenedioxythipohene)-Poly(Styrenesulfonate) (PEDOT:PSS) film printed via electrospray deposition. The printing setup was previously designed and constructed, wherein the syringe was loaded with the PEDOT:PSS and Isopropyl Alcohol (IPA) solution which was then printed onto thin and small sized Indium Tin Oxide (ITO) substrates under the application of a high voltage. The distance of the nozzle from the substrate was appropriately adjusted via the vertical linear movable stage before printing, as well as the voltage supply. Deposition time was set using an Arduino code that controlled the horizontal movement of the shutter attached to the bottom of the vertical linear aluminum frame. Horizontally and vertically induced vibrations were turned on during and post deposition to analyze the effect of both on the films’ properties through an ultrasonic transducer. The electrical sheet resistance of the PEDOT:PSS films was measured using a 4-point probe device and the surface contact angle of water on the PEDOT:PSS was measured using a contact angle meter. From the results obtained, it was concluded that the application ultrasonic vibrations improved wettability compared to the films printed without any vibrations. Furthermore, the electrical sheet resistance and contact angle of pure ITO was measured as a reference.
ContributorsRavishekar, Rohan (Author) / Li, Xiangjia (Thesis advisor) / Alford, Terry L (Thesis advisor) / Pathikonda, Gokul (Committee member) / Arizona State University (Publisher)
Created2023
Description
The measurement of the radiation and convection that the human body experiences are important for ensuring safety in extreme heat conditions. The radiation from the surroundings on the human body is most often measured using globe or cylindrical radiometers. The large errors stemming from differences in internal and exterior temperatures and indirect estimation of convection can be resolved by simultaneously using three cylindrical radiometers (1 cm diameter, 9 cm height) with varying surface properties and internal heating. With three surface balances, the three unknowns (heat transfer coefficient, shortwave, and longwave radiation) can be solved for directly. As compared to integral radiation measurement technique, however, the bottom mounting using a wooden-dowel of the three-cylinder radiometers resulted in underestimated the total absorbed radiation. This first part of this thesis focuses on reducing the size of the three-cylinder radiometers and an alternative mounting that resolves the prior issues. In particular, the heat transfer coefficient in laminar wind tunnel with wind speed of 0.25 to 5 m/s is measured for six polished, heated cylinders with diameter of 1 cm and height of 1.5 to 9 cm mounted using a wooden dowel. For cylinders with height of 6 cm and above, the heat transfer coefficients are independent of the height and agree with the Hilpert correlation for infinitely long cylinder. Subsequently, a side-mounting for heated 6 cm tall cylinder with top and bottom metallic caps is developed and tested within the wind tunnel. The heat transfer coefficient is shown to be independent of the flow-side mounting and in agreement with the Hilpert correlation.
The second part of this thesis explores feasibility of employing the three-cylinder concept to measuring all air-flow parameters relevant to human convection including mean wind speed, turbulence intensity and length scale. Heated cylinders with same surface properties but varying diameters are fabricated. Uniformity of their exterior temperature, which is fundamental to the three-cylinder anemometer concept, is tested during operation using infrared camera. To provide a lab-based method to measure convection from the cylinders in turbulent flow, several designs of turbulence-generating fractal grids are laser-cut and introduced into the wind tunnel.
ContributorsGupta, Mahima (Author) / Rykaczewski, Konrad (Thesis advisor) / Pathikonda, Gokul (Thesis advisor) / Middel, Ariane (Committee member) / Arizona State University (Publisher)
Created2024