Numerical Study of Roughness Effects on a NACA 0012 Airfoil Using a New Second-Order Closure of the Rough Wall Layer Modeling

2009 ◽  
Author(s):  
Meng-Huang Lu ◽  
William W. Liou
Keyword(s):  
Numerical Study ◽  
Wall Layer ◽  
Second Order ◽  
Rough Wall ◽  
Roughness Effects ◽  
Naca 0012

A case study in bifurcation theory

2017 ◽  
Vol 28 (08) ◽  
pp. 1750104 ◽  
Author(s):  
Youssef Khmou
Keyword(s):  
Dynamical Systems ◽  
Bifurcation Theory ◽  
Chaotic Behavior ◽  
Numerical Study ◽  
Logistic Map ◽  
Logistic Function ◽  
Second Order ◽  
Short Paper ◽  
Chaotic Region

This short paper is focused on the bifurcation theory found in map functions called evolution functions that are used in dynamical systems. The most well-known example of discrete iterative function is the logistic map that puts into evidence bifurcation and chaotic behavior of the topology of the logistic function. We propose a new iterative function based on Lorentizan function and its generalized versions, based on numerical study, it is found that the bifurcation of the Lorentzian function is of second-order where it is characterized by the absence of chaotic region.

scholarly journals AERODYNAMIC MODELING OF OSCILLATING WING IN HYPERSONIC FLOW: A NUMERICAL STUDY

2016 ◽  
Vol 42 ◽  
pp. 1660177
Author(s):  
JIAN ZHU ◽  
YING-YU HOU ◽  
CHEN JI ◽  
ZI-QIANG LIU
Keyword(s):  
Mach Number ◽  
Hypersonic Flow ◽  
Numerical Study ◽  
Unsteady Aerodynamics ◽  
Order Theory ◽  
Second Order ◽  
Double Wedge ◽  
Piston Theory ◽  
Impact Theory ◽  
Cfd Method

Various approximations to unsteady aerodynamics are examined for the unsteady aerodynamic force of a pitching thin double wedge airfoil in hypersonic flow. Results of piston theory, Van Dyke’s second-order theory, Newtonian impact theory, and CFD method are compared in the same motion and Mach number effects. The results indicate that, for this thin double wedge airfoil, Newtonian impact theory is not suitable for these Mach number, while piston theory and Van Dyke’s second-order theory are in good agreement with CFD method for Ma<7.

scholarly journals Tunable broadband-negative-permeability metamaterials by hybridization at THz frequencies

RSC Advances ◽  
2020 ◽  
Vol 10 (47) ◽  
pp. 28343-28350
Author(s):  
Thi Hien Nguyen ◽  
Son Tung Bui ◽  
Xuan Ca Nguyen ◽  
Dinh Lam Vu ◽  
Xuan Khuyen Bui
Keyword(s):  
Numerical Study ◽  
Second Order ◽  
Negative Permeability

We present a numerical study of thermo-tunable broadband-negative-permeability metamaterial based on second-order hybridization operating at the THz regime.

Numerical study of a transitional synthetic jet in quiescent external flow

2007 ◽  
Vol 581 ◽  
pp. 287-321 ◽  
Author(s):  
RUPESH B. KOTAPATI ◽  
RAJAT MITTAL ◽  
LOUIS N. CATTAFESTA III
Keyword(s):  
Numerical Study ◽  
Time Integration ◽  
Three Dimensional ◽  
Internal Flow ◽  
External Flow ◽  
Second Order ◽  
Synthetic Jet ◽  
Transition To Turbulence ◽  
Step Method ◽  
Fractional Step Method

The flow associated with a synthetic jet transitioning to turbulence in an otherwise quiescent external flow is examined using time-accurate three-dimensional numerical simulations. The incompressible Navier–Stokes solver uses a second-order accurate scheme for spatial discretization and a second-order semi-implicit fractional step method for time integration. The simulations are designed to model the experiments of C. S. Yao et al. (Proc. NASA LaRC Workshop, 2004) which have examined, in detail, the external evolution of a transitional synthetic jet in quiescent flow. Although the jet Reynolds and Stokes numbers in the simulations match with the experiment, a number of simplifications have been made in the synthetic jet actuator model adopted in the current simulations. These include a simpler representation of the cavity and slot geometry and diaphragm placement. Despite this, a reasonably good match with the experiments is obtained in the core of the jet and this indicates that for these jets, matching of these key non-dimensional parameters is sufficient to capture the critical features of the external jet flow. The computed results are analysed further to gain insight into the dynamics of the external as well as internal flow. The results indicate that near the jet exit plane, the flow field is dominated by the formation of counter-rotating spanwise vortex pairs that break down owing to the rapid growth of spanwise instabilities and transition to turbulence a short distance from the slot. Detailed analyses of the unsteady characteristics of the flow inside the jet cavity and slot provide insights that to date have not been available from experiments.

A preliminary numerical study of a swirling jet behind a circular disc

2008 ◽  
Vol 223 (5) ◽  
pp. 1127-1139
Author(s):  
H T Toh ◽  
R F Huang ◽  
M J Chern
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Saddle Points ◽  
Three Dimensional ◽  
Second Order ◽  
Circular Disc ◽  
Mean Velocity ◽  
Swirling Jet ◽  
First Case ◽  
Axis Of Symmetry

The three-dimensional flow fields behind a circular disc produced by an annular swirling jet alone and by an annular swirling jet with a central jet issuing from the disc centre are studied by solving the three-dimensional incompressible Navier—Stokes equations numerically using the solution algorithm of Hirt et al. ( Los Alamos Scientific Lab. Rept. LA-5852 (1970)). The swirl number and the Reynolds number based on the disc diameter and the volumetric mean axial velocity of the annular swirling jet are S=0.194 and Re=656, respectively. The convective and diffusive terms in the governing equations are discretized using the second-order central difference scheme. The resulting discretized equations are advanced in time using the second-order Runge—Kutta scheme. The simulation shows that the flow field behind the circular disc exhibit periodic oscillating behaviour, with the second case having a higher frequency due to the presence of the central jet. The mechanism responsible for this oscillating behaviour is identified and discussed. An analysis of the mean velocity fields in the mid-plane shows the existence of a stagnation point on the axis of symmetry in the first case and two saddle points off the axis of symmetry in the second case.

Small-scale characteristics of a turbulent boundary layer over a rough wall

1997 ◽  
Vol 342 ◽  
pp. 263-293 ◽  
Author(s):  
H. S. SHAFI ◽  
R. A. ANTONIA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Outer Layer ◽  
Large Scale ◽  
Energy Dissipation Rate ◽  
Wall Layer ◽  
Rough Wall ◽  
Small Scale ◽  
Smooth Wall ◽  
Velocity Derivative

Measurements of the spanwise and wall-normal components of vorticity and their constituent velocity derivative fluctuations have been made in a turbulent boundary layer over a mesh-screen rough wall using a four-hot-wire vorticity probe. The measured spectra and variances of vorticity and velocity derivatives have been corrected for the effect of spatial resolution. The high-wavenumber behaviour of the spectra conforms closely with isotropy. Over most of the outer layer, the normalized magnitudes of the velocity derivative variances differ significantly from those over a smooth wall layer. The differences are such that the variances are much more nearly isotropic over the rough wall than on the smooth wall. This behaviour is consistent with earlier observations that the large-scale structure in this rough wall layer is more isotropic than that in a smooth wall layer. Isotropy-based approximations for the mean energy dissipation rate and mean enstrophy are consequently more reliable in this rough wall layer than in a smooth wall layer. In the outer layer, the vorticity variances are slightly larger than those over a smooth wall; reflecting structural differences between the two flows.

scholarly journals Experimental and numerical study of wall layer development in a tribocharged fluidized bed

2018 ◽  
Vol 849 ◽  
pp. 860-884 ◽  
Author(s):  
Petteri Sippola ◽  
Jari Kolehmainen ◽  
Ali Ozel ◽  
Xiaoyu Liu ◽  
Pentti Saarenrinne ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Fluidized Bed ◽  
Numerical Study ◽  
Single Layer ◽  
Wall Layer ◽  
Small Scale ◽  
Average Charge ◽  
Particle Layer ◽  
Column Wall ◽  
Triboelectric Charging

The effects of triboelectricity in a small-scale fluidized bed of polyethylene particles were investigated by imaging the particle layer in the vicinity of the column wall and by measuring the pressure drop across the bed. The average charge on the particles was altered by changing the relative humidity of the gas. A triboelectric charging model coupled with a computational fluid dynamics–discrete element method (CFD-DEM) model was utilized to simulate gas–particle flow in the bed. The electrostatic forces were evaluated based on a particle–particle particle–mesh method, accounting for the surface charge on the insulating walls. It was found that simulations with fixed and uniform charge distribution among the particles capture remarkably well both the agglomeration of the particles on the wall and the associated decrease in the pressure drop across the bed. With a dynamic tribocharging model, the charging rate had to be accelerated to render the computations affordable. Such simulations with an artificial acceleration significantly over-predict charge segregation and the wall becomes rapidly sheeted with a single layer of strongly charged particles.

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