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Guarendi, Andrew NNumerical Investigations of Magnetohydrodynamic Hypersonic Flows
Master of Science, University of Akron, 2013, Mechanical Engineering
Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow are presented for both laminar and turbulent flow over a cylinder and flow entering a scramjet inlet. ANSYS CFX is used to carry out calculations for steady flow at hypersonic speeds (Mach number > 5). The low magnetic Reynolds number (<<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. Turbulence effects are accounted for when applicable and multiple turbulence models are compared. The results demonstrate the ability of the magnetic field to affect the flowfield, and variables such as location and magnitude of the applied magnetic field are examined. An examination of future work is provided through the implementation of a semi-discrete central scheme in-house code toward the solution of the Orszag-Tang vortex system.

Committee:

Abhilash Chandy, Dr. (Advisor); Scott Sawyer, Dr. (Committee Member); Alex Povitsky, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Hypersonic; Hypersonic Flow; Flow over a cylinder; Magnetohydrodynamic; MHD; Lorentz; Hypersonic MHD; Numerical Methods; CFD; Computational fluid dynamics; fluid dynamics; Aerospace;

Bruzzese, John ReedDevelopment Of An Electric Discharge Oxygen-Iodine Laser And Modelling Of Low-Temperature M=4 Flow Deceleration By Magnetohydrodynamic Interaction
Master of Science, The Ohio State University, 2008, Aeronautical and Astronautical Engineering
The present work addresses performance optimization of a small-scale, electric discharge excited, gasdynamic oxygen iodine laser (DOIL). For this, (i) nitric oxide has been added to the laser mixture, and (ii) iodine vapor was dissociated in an auxiliary electric discharge prior to its injection into the laser flow. The addition of NO has a significant effect on the laser performance, increasing small signal gain in the supersonic laser cavity from 0.05 %/cm to 0.08 %/cm. On the other hand, although large iodine dissociation fractions in the laser cavity have been achieved using an auxiliary discharge (up to 50%), only modest increase in gain was detected. The DOIL laser apparatus has been scaled up, with the main electric discharge volume increased by a factor of four and the flow rate through the laser doubled. The scaled-up laser has been tested using a nanosecond pulser / DC sustainer discharge or a capacitively coupled radio frequency discharge (CCRF) sustained at powers up to 2.7 kW and 4.5 kW, respectively. In both these cases, single-delta oxygen yield of up to 3-4% has been measured. Small signal gain up to 0.116 %/cm has been measured in the laser cavity while using the CCRF discharge to generate singlet delta oxygen. Numerical modeling of magnetohydrodynamic deceleration of a low-temperature M=4 flow was conducted using a three-dimensional compressible Navier-Stokes flow code. The results are in good agreement with recent experiments conducted at Ohio State, where flow deceleration by up to 2% has been demonstrated.

Committee:

Igor Adamovich (Advisor)

Subjects:

Engineering

Keywords:

DOIL; e-COIL; MHD; Magnetohydrodynamic; CFD; Laser; singlet delta oxygen;

Bennett, William ThomasComputational and Experimental Investigations into Aerospace Plasmas
Master of Science in Engineering (MSEgr), Wright State University, 2008, Mechanical Engineering
Investigations into two different fields of plasma research are presented here. These include the study of ion engine performance and the use of plasma discharges for flow control. In the area of ion engine performance, optimizing electron confinement is the primary goal of this work. The work of prior researchers was expanded through the study of the cathode emission location and the energy of the primary electrons. Cathode position was shown to have minimal effect on confinement length. For electron energy values greater than 20eV the effect on confinement length was also found to be very small. The strength of the magnetic field was also tested and compared with results from prior researchers. The results showed that for a magnet circuit that is already optimized, increasing the magnetic field strength through adding more magnets or using stronger magnets only decreases the confinement. In the area of plasma actuators for flow control, the objective is to garner a qualitative understanding of both heating and the addition of forces to subsonic and hypersonic flows. This was done through the use of a commercially available CFD package. Results showed that for plasma discharges the dominant effect on surface pressure in the hypersonic regime is that of heating. Representative force sources showed some effect but were smaller. Subsonic computational studies showed that heating had no significant effect on the pressure distribution. Results for the force sources show that it is possible to get some small changes in the surface pressure through the use of a sufficiently large force. Experimental results conducted in a subsonic wind tunnel confirmed the minimal influence of the heating effect. Long range Lorentz forces were obtained by placing magnets within the plate. The resulting forces on the plate match well with the Lorentz force law, but due to limitations in power, the plasma discharge did not reach the desired length.

Committee:

James Menart, PhD (Committee Chair); Scott Thomas, PhD (Committee Member); J. Mitch Wolff, PhD (Committee Member)

Subjects:

Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

plasma; MHD; hypersonic; joule heating

Rosenblatt, Heather LeahAsymptotics and Borel Summability: Applications to MHD, Boussinesq equations and Rigorous Stokes Constant Calculations
Doctor of Philosophy, The Ohio State University, 2013, Mathematics
We consider two problems where Borel summation based methods can be used to obtain information about solutions to differential equations. In the first problem, we analyze the initial value problem for the Boussinesq equation for fluid motion and temperature field as well as the magnetic Benard equation which models electro-magnetic effects on fluid flow under some simplifying assumptions. This method has previously been applied to the Navier-Stokes equation, which is a limiting case for each of these equations. We show that this approach can be used to prove local existence for the Boussinesq and magnetic Benard equation, in two or three dimensions. We prove that an equivalent system of integral equations in each case has a unique solution, which is exponentially bounded for p on the positive real line, p being the Laplace dual variable of 1/t. This implies local existence of a classical solution to the Boussinesq and magnetic Benard equations in a complex t-region that includes a real positive time axis segment. Further, it is shown that within this real time interval, for analytic initial data and forcing f, the solution remains analytic and has the same analyticity strip width. Further, under these conditions, the solution is Borel summable, implying that the formal series in time is Gevrey-1 asymptotic for small t. We also determine conditions on the computed solution to the integral equation in each case over a finite interval in p that results in a better estimate for existence time for the corresponding solution to the partial differential equation. The second problem is to give rigorous bounds on the Stokes constant values for a nonlinear ordinary differential equation (ODE) that arises in the context of selection of limiting finger width in viscous fingering -the so called Saffman-Taylor problem. Specifically, it was proved that the selected finger width asymptotically corresponds to values of a parameter C in a nonlinear ODE such that the Stokes constant on the real positive line vanishes. The full asymptotic expansion for the solution includes not only inverse powers of the independent variable, but also exponentially small corrections. We prove rigorous estimates on the Stokes constant and find intervals in C for which the Stokes constant vanishes, in agreement with earlier numerical computations.

Committee:

Saleh Tanveer (Advisor)

Subjects:

Mathematics

Keywords:

PDE; Asymptotics; Borel summability; MHD; Boussinesq; Stokes constants

Kalapurakal, DipinNumerical Simulation of Magnetohydrodynamic (MHD) Effect on Forced, Natural and Mixed Convection Flows
Master of Science in Engineering, University of Akron, 2012, Mechanical Engineering
The accurate simulation of magnetohydrodynamic (MHD) ows and heat transfer is critical to the understanding of the complex physics in liquid metal flows for coolant and breeder blankets used in fusion power plants such as tokamaks, metallurgy,aerospace applications and crystal growth. These issues will be addressed through an effort investigating low-magnetic Reynolds number (Rem), high-Hartmann number(Ha), MHD flows in a square cavity, using a 2D parallel vorticity-streamfunction-based incompressible Navier-Stokes code. Numerical simulations of MHD flow and heat transfer are carried out in a square cavity with emphasis on specific classical benchmark problems like the lid-driven cavity with and without heat transfer (forced convection), natural convection and mixed convection (forced + natural). Effects of Ha and Pr are investigated to assess MHD in heat transfer under various conditions. Quantities analyzed include streamfunction, vorticity, velocities, temperature and Nusselt number. Computations are carried out on in-house supercomputing desktops and clusters. This study provides a fundamental understanding of MHD effects on flow behavior and heat transfer in the context of a series of simple benchmark problems. Also created through this eort is an accurate and efficient incompressible code capable of calculating a variety of added complex physics in fluid mechanics.

Committee:

Abhilash J. Chandy, Dr. (Advisor); Alex Povitsky, Dr. (Committee Member); Gaurav Mittal, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Numerical simulation; MHD; Magnetohydrodynamcis; driven cavity; Forced convection; Natural convection;Mixed convection