Çelikkıran, Mehmet Emin
Turbulence and transition to turbulence are still one of the unresolved topics in physics. Multiphase applications of the transitional flows are more complex than their single-phase counterparts due to having many options for the source of instability. From oceanography to rocket engines, from oil industry to astrophysical phenomena, multiphase instabilities have many examples in both nature and industry. Acquiring the knowledge of the starting point of transition is crucial in all these applications. In this study focus is the instability of multiphase flows, especially the instabilities at interfaces. Linear hydrodynamic stability approach is used, and the Orr-Sommerfeld equation is solved in order to capture the behavior of perturbations. For multiphase flow, Orr-Sommerfeld equations for each phase are built, and interface conditions are applied to connect individual phases. The Reynolds number is not the only dimensionless parameter for multiphase flows to affect the perturbations and instability. Stratifications of density and viscosity, the effect of surface tension, gravity, and derivatives of mean velocity profiles will all have characteristic effects on the instabilities at the interface. A spectral method, Chebyshev Collocation method, is used for discretization. Matlab, Octave, and C++ programming languages are used for validation cases. Validation of codes for both single-phase and multiphase flow is acquired by the comparison of numerical results and results from the literature.


A stabilized finite element method for the two-field and three-field Stokes eigenvalue problems
Türk, Önder; Codina, Ramon (2016-10-01)
In this paper, the stabilized finite element approximation of the Stokes eigenvalue problems is considered for both the two field (displacement pressure) and the three-field (stress displacement pressure) formulations. The method presented is based on a subgrid scale concept, and depends on the approximation of the unresolvable scales of the continuous solution. In general, subgrid scale techniques consist in the addition of a residual based term to the basic Galerkin formulation. The application of a stand...
Laser sheet visualization for flapping motion in hover
Kurtuluş, Dilek Funda; Farcy, Alain; Alemdaroglu, Nafiz (American Institute of Aeronautics and Astronautics Inc.; 2006-12-01)
The aim of the present study is to understand the aerodynamics phenomena and the vortex topology of the highly unsteady flapping motion. Instead of the use of real insect/bird wing geometries and motions which are highly complex and difficult to imitate by an exact modeling, a simplified model is used to understand the unsteady aerodynamics and vortex formation during the different phase of the flapping motion.
A Computational analysis on rotor-propeller arm interaction in hovering flight
Yener, Serkan.; Perçin, Mustafa; Department of Aerospace Engineering (2019)
This study presents a computational analysis on the interaction between rotor and different rotor frame-arm geometries in hovering flight. The influence of the frame arm on the aerodynamic performance of the rotor is assessed by using commercially available computational fluid dynamics (CFD) solver software ANSYS Inc. Fluent 17. Numerical results are validated for hovering and forward vertical climb flight conditions with thrust and torque measurements conducted on a 16x4 carbon fiber propeller. The thrust ...
çolak, ılgın; Perçin, Mustafa; Çıray, Cahit; Department of Aerospace Engineering (2022-2-8)
Turbulence is an important phenomenon in aerospace sciences, but it still has aspects that are not fully illuminated. In order to understand the physical mechanisms of turbulence, it is crucial to consider it in terms of eddies. Eddies are the groups of fluid particles that move together and preserve a certain identity for a while, and they constitute the building blocks of turbulence. The motion of eddies in the course of their life span can be expressed as dispersive wave motion. This requires a dispersio...
A Parametrical Study with Laser Sheet Visualization for an Unsteady Flapping Motion
Kurtuluş, Dilek Funda; Farcy, Alain; Alemdaroğlu, Hüseyin Nafiz (2006-06-08)
In order to better understand the vortex dynamics and evaluation of the flow structures during the unsteady flapping motion, experimental visualizations are considered. The visualizations are represented for the phenomenological analysis of the flow. The flow is assumed to be laminar with the Reynolds number of 1000. The evaluation of the complex flow topology is investigated instantaneously for the effect of the different parameters. The vortex identification is performed for the change of incidence positi...
Citation Formats
M. E. Çelikkıran, “A SPECTRAL APPROACH FOR SOLVING TWO-FLUID FLOW STABILITY PROBLEM,” M.S. - Master of Science, Middle East Technical University, 2022.