Computation of Aerodynamic Forces Under Nonequilibrium Conditions: Flow Past a Spinning Cylinder

AIAA Journal ◽  
2018 ◽  
Vol 56 (11) ◽  
pp. 4219-4224 ◽  
Author(s):  
Benzi John ◽  
Xiao-Jun Gu ◽  
David R. Emerson
Keyword(s):  
Aerodynamic Forces ◽  
Flow Past ◽  
Nonequilibrium Conditions ◽  
Spinning Cylinder

Characteristics of Flow Past a Symmetric Airfoil at Low Reynolds Number: A Nonlinear Perspective

2012 ◽  
Author(s):  
M. Saif Ullah Khalid ◽  
Imran Akhtar
Keyword(s):  
Reynolds Number ◽  
Period Doubling ◽  
Nonlinear Behavior ◽  
Phase Portraits ◽  
Aerodynamic Forces ◽  
Flow Past ◽  
Time Histories ◽  
Lift And Drag ◽  
Naca 0012 ◽  
Even Harmonics

Flow separation in airfoils have been extensively studied to analyze the underlying physics of the phenomenon. The phenomenon being nonlinear requires tools to reveal various features involving stall, bifurcation, and transition to chaos. In this study, we perform numerical simulations of the flow past a symmetric airfoil (NACA-0012) at 1,000 Reynolds number to compute the aerodynamic forces at different angles of attack (α). The time histories and spectral analysis reveal important features of nonlinear behavior in the flow around the airfoil. We find that the steady state temporal solutions for aerodynamic forces; lift and drag, contain both odd and even harmonics which indicate the presence of quadratic as well as cubic nonlinearity in the system. These results also help to understand nonlinear behavior of the system as a function of α. Considering the angle of attack for airfoil as a control parameter, we observe that to achieve the static stall, flow becomes chaotic adopting a route through period-doubling and quasi-periodic regimes. Using phase portraits and Poincare maps between the states of the system, period-doubling is observed in this nonlinear system at α = 22° leading to chaos at α = 27°.

scholarly journals Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder

2014 ◽  
Vol 26 (10) ◽  
pp. 104101 ◽  
Author(s):  
Philippe Meliga ◽  
Edouard Boujo ◽  
Gregory Pujals ◽  
François Gallaire
Keyword(s):  
Turbulent Flow ◽  
Square Cylinder ◽  
Aerodynamic Forces ◽  
Flow Past ◽  
Laminar And Turbulent Flow

Aerodynamic excitation of the harmonium reed

1971 ◽  
Vol 49 (4) ◽  
pp. 803-816 ◽  
Author(s):  
Arthur O. St Hilaire ◽  
Theodore A. Wilson ◽  
Gordon S. Beavers
Keyword(s):  
Growth Rate ◽  
Flow Visualization ◽  
Flow Velocity ◽  
Potential Flow ◽  
The Self ◽  
Aerodynamic Forces ◽  
Flow Past ◽  
Wake Instability

An investigation of the mechanism responsible for the self-excited oscillations of a harmonium reed is presented. Experiments show that the amplitude of vibration of the reed grows exponentially, and measurements of the growth rate as a function of the flow past the reed are reported. Flow visualization studies lead to the conclusion that jet or wake instability is not important in exciting the reed vibration. An analysis of the flow around the reed as an unsteady potential flow results in the evaluation of the aerodynamic forces exciting the reed. The analysis shows that the pressure which excites the reed motion is of the order of $\rho U_0\dot{a}$, where U0 is the flow velocity and $\dot{a}$ is the reed velocity.

Three-Dimensional Instabilities in Flow Past a Rotating Cylinder

2004 ◽  
Vol 71 (1) ◽  
pp. 89-95 ◽  
Author(s):  
S. Mittal
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Side Wall ◽  
Navier Stokes ◽  
Stabilized Finite Element ◽  
Stabilized Finite Element Method ◽  
Flow Past ◽  
Two Dimensional Flow ◽  
Spinning Cylinder ◽  
Set Up

Flow past a spinning circular cylinder placed in a uniform stream is investigated via three-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier-Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and freestream speed of the flow is 200. The nondimensional rotation rate, α, (ratio of the surface speed and freestream speed) is 5. It is found that although the two-dimensional flow for α=5 is stable, centrifugal instabilities exist along the entire span in a three-dimensional set-up. In addition, a “no-slip” side-wall can result in separation of flow near the cylinder ends. Both these effects lead to a loss in lift and increase in drag. The end conditions and aspect ratio of the cylinder play an important role in the flow past a spinning cylinder. It is shown that the Prandtl’s limit on the maximum lift generated by a spinning cylinder in a uniform flow does not hold.

Microstructural observations of the “Wustite-Spinel” coexistence following quenching of cation-excess spinels, Ni2(1+x)Ti1-xO4

1990 ◽  
Vol 48 (4) ◽  
pp. 1058-1059
Author(s):  
Ian M. Anderson ◽  
Arnulf Muan ◽  
C. Barry Carter
Keyword(s):  
Film Growth ◽  
Spinel Phase ◽  
Model Systems ◽  
Ion Milling ◽  
Coexistence Of Phases ◽  
Nonequilibrium Conditions ◽  
Diffraction Patterns ◽  
Spinel Structures ◽  
Highly Porous ◽  
Standard Techniques

Oxide mixtures which feature a coexistence of phases with the wüstite and spinel structures are considered model systems for the study of solid-state reaction kinetics, phase boundaries, and thin-film growth, and such systems are especially suited to TEM studies. (In this paper, the terms “wüstite” and “spinel” will refer to phases of those structure types.) The study of wüstite-spinel coexistence has been limited mostly to systems near their equilibrium condition, where the assumptions of local thermodynamic equilibrium are valid. The cation-excess spinels of the type Ni2(1+x)Ti1-xO4, which reportedly exist only above 1375°C4, provide an excellent system for the study of wüstite-spinel coexistence under highly nonequilibrium conditions. The nature of these compounds has been debated in the literature. X-ray and neutron powder diffraction patterns have been used to advocate the existence of a single-phase, non- stoichiometric spinel. TEM studies of the microstructure have been used to suggest equilibrium coexistence of a stoichiometric spinel, Ni2TiO4, and a wüstite phase; this latter study has shown a coexistence of wüstite and spinel phases in specimens thought to have been composed of a single, non- stoichiometric spinel phase. The microstructure and nature of this phase coexistence is the focus of this study. Specimens were prepared by ball-milling a mixture of NiO and TiO2 powders with 10 wt.% TiO2. The mixture was fired in air at 1483°C for 5 days, and then quenched to room temperature. The aggregate thus produced was highly porous, and needed to be infiltrated prior to TEM sample preparation, which was performed using the standard techniques of lapping, dimpling, and ion milling.

Sign in / Sign up

Export Citation Format

Share Document