Degree Type

Dissertation

Date of Award

2021

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

Major

Aerospace Engineering

First Advisor

Hui Hu

Abstract

Atmospheric icing is one of the major problems faced in cold regions. The problems caused by the icing mainly has adverse effect on several engineering structures and machines. For instance, the electric power transmission cables, aircrafts wings and other critical components exposed to atmosphere, wind turbines, suspension bridge cables etc. are some of the engineering structures which are severely affected by atmospheric icing. Some of the icing events can have very critical after-effects. In recent years the damaging effect of atmospheric icing on transmission lines has become an increasingly important. As we become more dependent on reliable energy and communications, even in remote areas, transmission line failure is a costly inconvenience at the very least, and it can threaten human life. At the same time, it is desirable to minimize construction and maintenance costs. These circumstances have called for more research into the causes of atmospheric icing and its effects on transmission lines. Significant progress must be made in our understanding of the problem. One of the most important factors that need attention is the understanding of the combined effect of the wind and the shape of accreted ice on the loads exerted on a conductor. In this study, experimental investigations were conducted to examine the dynamic ice accretion process over the surface of a high-voltage power transmission cable model and characterize the effects of the ice accretion on the aerodynamic forces acting on the test model. The experimental study was carried out by leveraging the unique Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) to generate typical wet glaze and dry rime icing conditions experienced by power transmission cables. In the first phase of the study, a cylindrical power cable model, which has the same diameter as that of typical power transmission cables, was mounted in ISU-IRT for the ice accretion experiments. In addition to using a high-speed digital imaging system to record the dynamic ice accretion process, a novel digital image projection (DIP) based technique was utilized to quantify the 3D shapes of the ice structures accreted on the surface of the power cable model as a function of the ice accretion time. The time variations of the aerodynamic drag force acting on the test model during the dynamic ice accretion process were also measured quantitatively by using high-sensitive force/moment transducers mounted at the two ends of the test model. In the second phase, an aluminum conductor steel reinforced (ACSR) model, which is the most commonly used type of transmission cable model was investigated in the same manner. In the third phase, a series of two ACSR conductors (bundled conductors) were used to understand the effects of the presence of the windward conductor on the ice accretion of the leeward conductor. The ice structures accreted over the surface of the power cable model were found to change significantly under different icing conditions (i.e., rime icing vs. glaze icing). The characteristics of the aerodynamic drag acting on the test model was found to vary significantly during the dynamic ice accretion process, highly dependent on the type of ice structure which accreted on the test model. The acquired snapshots of the ice accretion images and the measured 3D shapes of the accreted ice structures on the test model are correlated with the aerodynamic force measurement results to elucidate the underlying physics. The icing characteristics of smooth cylinder was different from the ACSR conductor indicating that the effects of icing is dependent on the outer profile of the conductor. The ACSR conductor accreted much more ice and was subjected to more severe drag forces. The study using bundled conductors revealed that the effects of icing on the leeward conductor are significantly modified by the presence of a windward conductor. In the next phase, several anti-icing techniques have been investigated. Very recently, dielectric barrier discharge (DBD) plasma actuation has been suggested as a promising, alternative anti-/de-icing method, by leveraging the thermal effects induced by DBD plasma generation. Several anti-icing hydrophobic and super hydrophobic coatings and hybridization with DBD plasma were also investigated and was found to be effective in mitigating the effects of icing. The final phase of the study was conducted in the black wind tunnel at IOWA state university. This study aimed to establish a metamodeling-based technique to optimize the parameters of a dielectric barrier discharge (DBD) plasma used for flow separation over the surface of a wind turbine model in deep stall. The applied voltage and frequency for the NS-DBD plasma actuation were used as the design variables to demonstrate the optimization procedure. The highest possible lift coefficient of the turbine airfoil model at deep stalled angles of attack (i.e., α = 22⁰ and 24⁰) were selected as the objective function for the optimization. It was found that, while the metamodeling-based procedure could accurately predict the objective function within the bounds of the design variables with an uncertainty ~ 2%, a global accuracy level of ~97% was achieved within the whole design space.

DOI

https://doi.org/10.31274/etd-20210609-192

Copyright Owner

Ramsankar Veerakumar

Language

en

File Format

application/pdf

File Size

208 pages

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