## Type of Work

Article (34) Book (0) Theses (6) Multimedia (0)

## Peer Review

Peer-reviewed only (40)

## Supplemental Material

Video (0) Audio (0) Images (0) Zip (0) Other files (0)

## Publication Year

## Campus

UC Berkeley (1) UC Davis (1) UC Irvine (21) UCLA (0) UC Merced (0) UC Riverside (0) UC San Diego (0) UCSF (2) UC Santa Barbara (1) UC Santa Cruz (2) UC Office of the President (2) Lawrence Berkeley National Laboratory (14) UC Agriculture & Natural Resources (0)

## Department

Research Grants Program Office (RGPO) (2) Physics Department (1)

## Journal

## Discipline

Medicine and Health Sciences (6) Life Sciences (2)

## Reuse License

BY - Attribution required (7) BY-NC-ND - Attribution; NonCommercial use; No derivatives (1)

## Scholarly Works (40 results)

A numerical simulation was performed for a 2D plasma flow control of flow around a circular cylinder at Reynolds number 6.6e3.

The plasma actuator model proposed by Suzen et al. was used. Poisson equations for the electric potential and the charge density were solved to compute the body force field. The body force generated by the plasma actuator model was incorporated into the flow solver as source terms for the momentum equations.

The simulation with plasma actuators demonstrated a smaller wake and reduced vortex shedding behind the cylinder compared to the reference case without the actuators. The influence of the locations of the plasma actuators was investigated with a parametric study. The results indicate that the effectiveness of the plasma actuation is sensitive to the actuator locations.

A thermodynamic property of gases called the fundamental derivative was first proposed by Bethe(1942) and later defined as the dimensionless quantity $\Gamma=\dfrac{c^4}{2v^3}\left(\dfrac{\partial^2 v}{\partial p^2}\right)_s$. The sign of $\Gamma$ reflects the sign of the curvature of the isentrope in the pressure-specific volume plane. The value of $\Gamma$ significantly affects the gas behavior and flow properties. Gases at relatively low pressure away from the critical pressure levels usually have values of $\Gamma$ above 1.0. For an ideal gas, $\Gamma = \dfrac{\gamma +1}{2}$, where $\gamma$ is the ratio of specific heats. Previous studies identified flow behaviors of gases with $\Gamma <0$ that are qualitatively opposite to classical gas dynamic theories based on perfect gas laws. For example, a divergent channel accelerates a subsonic flow and expansion shocks exist for gases with negative $\Gamma$. Although no experimental evidence has yet been found to confirm such non-classical gas flow behaviors, present interests in the use of super-critical heavy gases as well as pure academic curiosity call for more in-depth and definitive studies of such gas flows. A dense gas called $MDM$ is selected as the working fluid in the present work. A region of negative fundamental derivative is found near the critical point using the Van der Waals real gas Equation of State (EoS) for this heavy gas. Contrary to previous studies, the present work considers $\Gamma$ as a local thermodynamic variable instead of a constant in an isentropic flow or across a shock wave. Formulas of the relation of the fundamental derivative to other thermodynamic variables are given. To compare with the ideal gas model, the thermodynamic properties of this dense gas and the gas dynamic behaviors near its critical point are investigated. The conservation laws have been applied to develop the ordinary differential equation system for the quasi-one-dimensional isentropic flow. Since analytical solutions as in the classical theory are no longer possible for the non-ideal gas, numerical simulations are obtained for different upstream conditions. Various seemingly counter-classical gas dynamics flow behaviors are demonstrated. For example, a divergent-convergent nozzle is needed for transonic flow when the gas is within the negative fundamental derivative range. These unconventional gas behaviors are vitally interrelated in a flow of such non-ideal gas as it expands from high pressure to low pressure going through regions of $\Gamma >1$, $0<\Gamma <1$, and $\Gamma <0$ due to changes of its thermodynamic properties in the isentropic expansion process. Specific counter-classical behaviors are identified and discussed in this thesis.

A Navier-Stokes Computational Fluid Dynamics (CFD) code is coupled with a Computa-

tional Structural Dynamics (CSD) code to study the flutter boundary of the NACA64A010

airfoil using Isogai’s structural model in transonic conditions. This model simulates aeroelas-

tic conditions on a sweptback wing. A well-known feature, only present in the inviscid flutter

boundary of this airfoil, is the existence of multiple flutter points for a fixed freestream Mach

number. The fully-turbulent flutter boundary has not been studied by many researchers us-

ing a Reynolds-Averaged Navier-Stokes approach. In the present study, the fully-turbulent

flutter boundary reveals the existence of multiple equilibrium positions for a narrow range

of flight conditions. The system moves away from the initial equilibrium position, finding a

new set of equilibrium points and oscillating around it. This new set of equilibrium points

reveals as stable or unstable for different structural properties of the wing.

We then proceed to study the effect of turbulent transition on flutter boundary. A laminar-

to-turbulent transition model is implemented in the CFD code and validated. The effect of

using a free-transition CFD code vs. a fully-turbulent approach is evaluated on three airfoils

with different characteristics for subsonic and transonic conditions. While free-transition

does not affect the pressure distribution at subsonic conditions, the transonic simulations

reveal a change in the shock-wave position when laminar-turbulent effects are included. The

effect of transition on the flutter boundary of the NACA64A010 airfoil at transonic conditions

is then investigated. A comparison between the free-transition, inviscid and fully-turbulent

flutter boundaries reveals similarities between the inviscid and free-transition elastic re-

sponses. Those similarities are due to the shift in the fully-turbulent shock-wave position,

when accounting for free-transition effects, moving closer to the inviscid shock location.

This dissertation proposes numerical methods for the Euler and Navier-Stokes equations with spectral discretization in time and a fast space-time coupled LU-SGS (ST-LU-SGS) method for solving the resultant implicit equations. Firstly, the Fourier time spectral method is studied for periodic problems with test cases. The problem of non-symmetric solutions for symmetric periodic flow problems, caused by odd numbers of intervals in a period, is discovered and discussed in detail. The requirement of ensuring symmetric solution is proposed. In problems where frequency is not known a priori, a new frequency search approach based on Fourier analysis of the lift coefficient is proposed to work with the time spectral method. Computational results show that initial guesses of the frequency far away from the exact value can be used if the new approach is applied before employing a gradient based method. A new Chebyshev time spectral method is proposed to solve non-periodic unsteady problems and is validated by test cases. Computational results show that this method is very efficient in simulating both periodic and non-periodic unsteady flows, especially the non-periodic problems.

The use of Fourier or Chebyshev spectral discretization in time results in implicit equations in time marching. Explicit Runge-Kutta methods have often been used to solve such implicit system of equations through the use of the dual-time stepping algorithm. Such methods are, however, slow despite the use of acceleration schemes such as implicit residual smoothing and multigrid. We propose a new space-time LU-SGS (ST-LU-SGS) implicit scheme for both the Fourier and Chebyshev time spectral methods. In this scheme, the time domain is regarded as one additional dimension in space. Computational experiments show that this new scheme is faster than the explicit Runge-Kutta solver. For Navier-Stokes flow test cases, computations using the ST-LU-SGS implicit scheme is over ten times faster than the explicit Runge-Kutta solver. The ST-LU-SGS implicit scheme also works very well with the proposed frequency search approach. The ST-LU-SGS scheme is as efficient as the Block-Jacobi implicit algorithm and is more robust than the Block-Jacobi implicit algorithm. The proposed ST-LU-SGS scheme works for problems with either low frequency or high frequency while the Block-Jacobi implicit algorithm fails for high frequency flow problems.

This thesis explores linear and non-linear computational methods for solving unsteady flow. The eventual goal is to apply these methods to two-dimensional and three-dimensional flutter predictions. In this study the quasi-one-dimensional nozzle is used as a framework for understanding these methods and their limitations. Subsonic and transonic cases are explored as the back-pressure is forced to oscillate with known amplitude and frequency. A steady harmonic approach is used to solve this unsteady problem for which perturbations are said to be small in comparison to the mean flow. The use of a linearized Euler equations (LEE) scheme is good at capturing the flow characteristics but is limited by accuracy to relatively small amplitude perturbations. The introduction of time-averaged second-order terms in the Non-Linear Harmonic (NLH) method means that a better approximation of the mean-valued solution, upon which the linearization is based, can be made. The nonlinear time-accurate Euler solutions are used for comparison and to establish the regimes of unsteadiness for which these schemes fails. The usefulness of the LEE and NLH methods lie in the gains in computational efficiency over the full equations.

The first part of this dissertation explores harmonic methods for both one-dimensional and quasi-one-dimensional flows. The focus is placed on the flow response to oscillating back-pressure for subsonic and transonic conditions. This study includes insight as to the applicability of these methods when resonance of the flow field is expected and estimates of the errors introduced when applying a linearization about a steady-state non-linear flow. The second part explores the unsteady aerodynamics and performance of NASA Rotor 67 when time-varying inlet-distortions are used. A Detached-Eddy Simulation is used to model the flow physics. Within this study, the impact of the inlet distortions are presented based on the unsteady aerodynamics and performance metrics as well as the tonal content of pressure fluctuations within the rotor passage.

It is well recognized that nitric oxide (NO) is involved in tumor progression, including melanoma. Measurement of proliferative and metastatic capacity by MTS and Matrigel invasion assays, respectively, was done and showed that NO-treated melanoma cells exhibited a higher capacity compared with control, especially metastatic Lu1205 cells. Apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE/Ref-1) is a multifunctional protein and its role in tumor biology has attracted considerable attention. To determine whether APE/Ref-1 plays a role in mediating NO stimulation of melanoma progression, we investigated the effect of DETA/NO on levels of APE/Ref-1 and related downstream targets [activator protein-1 (AP-1)/JunD, matrix metalloproteinase-1 (MMP-1), Bcl-2, and inducible nitric oxide synthase (iNOS)] by Western blot and reverse transcription-PCR analysis. Following DETA/NO treatment, APE/Ref-1 and other downstream molecules were induced. Knockdown of APE/Ref-1 or AP-1/JunD by specific small interfering RNA markedly reversed the induction by NO stress of target proteins. These results present evidence for the existence of a functional feedback loop contributing to progression and metastasis of melanoma cells. Resveratrol has been shown to be an APE/Ref-1 inhibitor and significant decreases in AP-1/JunD, MMP-1, Bcl-2, and iNOS protein levels occurred after exposure to resveratrol. This phenolic antioxidant may be an appropriate choice for combining with other compounds that develop resistance by up-regulation of these molecules.