Numerical and Experimental Studies of Oscillatory Airflows Induced by Rotation of a Grass-Cutting Blade

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
F. Abbasian ◽  
J. Cao ◽  
S. D. Yu
Keyword(s):  
Background Noise ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Tetrahedral Mesh ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Unstructured Tetrahedral Mesh ◽  
The Stability ◽  
Mesh Convergence

Three-dimensional oscillatory airflows induced by a rotating grass-cutting blade in a cylindrical chamber are studied experimentally and numerically in this paper. Experimental pressure results are obtained using a sound pressure transducer and a data acquisition system. The measured pressure data contain background noise and high-frequency sound signals due to the blade vibrations. The background noise is separately measured; its effect on the signal is determined from a spectral subtraction algorithm. A time-accurate finite volume numerical solution to the three-dimensional incompressible unsteady Navier–Stokes equations is also sought using the sliding frame technique and the unstructured tetrahedral mesh. Convergence studies are conducted using various combinations of mesh sizes and time increments to ensure the stability of the numerical scheme. The experimental and numerical pressure results are in good agreement.

Some stability results on global solutions to the Navier–Stokes equations

Analysis ◽  
2015 ◽  
Vol 35 (3) ◽  
Author(s):  
Isabelle Gallagher
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Global Solutions ◽  
Navier Stokes ◽  
Smooth Solutions ◽  
Navier Stokes Equations ◽  
Global Smooth Solutions ◽  
Whole Space ◽  
The Stability ◽  
Stability Results

AbstractIn these notes we present some results concerning the existence of global smooth solutions to the three-dimensional Navier–Stokes equations set in the whole space. We are particularly interested in the stability of the set of initial data giving rise to a global smooth solution.

Linear Stability Analysis of LPT Rotor Packets: Part II — Three-Dimensional Results and Mistuning Effects

2004 ◽  
Author(s):  
Roque Corral ◽  
Juan Manuel Gallardo ◽  
Carlos Vasco
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Stability Limit ◽  
Mode Shapes ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Reduced Frequency ◽  
Stability Maps ◽  
The Stability ◽  
The One

Part II of this paper compares the aerodynamic damping of a modern Low Pressure Turbine (LPT) interlock bladed-disc to the one obtained when the blades are welded in pairs through the lateral face of the shroud. The damping is computed using the linearized Reynolds averaged Navier-Stokes equations on a moving grid. It is concluded that the increase in stability of the welded-pair with respect the cantilever configuration due to the modification of the mode-shapes, is smaller than the one due to the overall raise of the reduced frequencies of a bladed-disc with an interlock design. The modification of the flutter boundaries due to mistuning effects is taken into account using the reduced order model known as the Fundamental Mistuning Model (FMM). It is shown that the modification on the stability limit of a interlock bladed-disc is negligible, while for a welded-pair configuration an increase of 0.15% on the critical damping may be expected. Two realistic welded-pair bladed-discs are analysed in this work. It is shown that both are aerodynamically unstable, which is in agreement with the experimental observations. Critical reduced frequency stability maps accounting for mistuning effects are derived for both, freestanding and welded in pairs airfoils. The airfoils are assumed to be identical and mechanically uncoupled. The stabilizing effect of mistuning is also retained in these maps.

A HYBRID FINITE-ANALYTIC ALGORITHM FOR SOLVING THREE-DIMENSIONAL ADVECTION-DIFFUSION EQUATIONS

2004 ◽  
Vol 01 (03) ◽  
pp. 407-430 ◽  
Author(s):  
H. M. HU ◽  
K.-H. WANG
Keyword(s):  
Convergence Rates ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Diffusion Equations ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Advection Diffusion Equation ◽  
Advection Diffusion ◽  
The Stability

The hybrid finite-analytic (HFA) method for discretization of a three-dimensional advection-diffusion equation is developed using the superposition of the HFA solutions of locally linearized one-dimensional advection-diffusion equations. An example calculation of a system of three-dimensional nonlinear equations is conducted to test the convergence and accuracy of the 7-point numerical scheme. Good agreements between calculated and analytical solutions are obtained. An algorithm based on the HFA method with multigrid technique and Gauss-Seidel iteration is also developed to solve the three-dimensional Navier-Stokes equations in a staggered grid system. The stability and efficiency of the method are demonstrated by performing calculations of the fluid flow in a three-dimensional cubic cavity with a moving top wall. The proposed procedure is observed to exhibit good rates of smoothing and almost grid-independent convergence rates in comparison with a single-grid iteration method. The results are in excellent agreement with other published computational results.

Sensitivity Analysis With Respect to Flutter-Free Design of Compressor Blades

2010 ◽  
Author(s):  
Markus May
Keyword(s):  
Sensitivity Analysis ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Compressor Blades ◽  
Similarity Parameter ◽  
Navier Stokes Equations ◽  
Stability Behaviour ◽  
The Stability ◽  
German Aerospace

In this paper, the rotor geometries of two consecutive design loops are compared numerically with respect to aeroelastic stability. Therefore, the TRACE code of the German Aerospace Center DLR is used to compute the flutter predictions: based on a three-dimensional steady solution, the time-linearized Navier-Stokes equations are solved in order to assess the aerodynamic damping so that the critical inter-blade phase angles can be determined. Apart from the global stability behaviour the computation of local excitation per surface area is presented, facilitating the identification of stabilizing and destabilizing effects due to blade motion and flow field disturbances. Aiming for flutter-free design of compressor blades, an exemplary sensitivity analysis on the first mode is performed. Within the scope of this study, reduced frequency and mass ratio are varied and the influence of these parameters on the stability behaviour is deduced. For a tuned system, the nondimensional flutter equations are derived introducing the flutter index as aeroelastic similarity parameter. Differing tendencies of the aerodynamic work entry and the corresponding logarithmic decrement concerning flutter susceptibility are discussed in detail.

Image-Based Computational Fluid Dynamics in a Carotid Artery

2009 ◽  
Author(s):  
F. Gori ◽  
A. Boghi
Keyword(s):  
Carotid Artery ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Tetrahedral Mesh ◽  
Navier Stokes ◽  
Patient Specific ◽  
Navier Stokes Equations ◽  
3D Geometry ◽  
Specific Geometry ◽  
Flow Through

Literature presents numerical simulations on image-based geometry where blood is treated as a Newtonian fluid, while others simulations assumed a non-Newtonian blood with two or three-dimensional axisymmetric geometry. The present work investigates the non-Newtonian behavior of a pulsating blood flow through a stenosed carotid artery, realistically reconstructed with the patient-specific geometry of a 60 years old man with an intimal thickening of 90% degree of stenosis. Lumen boundary contours are segmented using commercial image-processing software AMIRA for a 3D geometry reconstruction. High-quality tetrahedral mesh is generated using commercial mesh-generator code GAMBIT. The 3-D unsteady incompressible Navier-Stokes equations are solved using the commercial finite volume code FLUENT. The boundary condition is assumed from a flow-rate-wave of the literature using the FFT method and imposing a pressure sinusoidal signal with 20 harmonics.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

2020 ◽  
Vol 14 (4) ◽  
pp. 7369-7378
Author(s):  
Ky-Quang Pham ◽  
Xuan-Truong Le ◽  
Cong-Truong Dinh
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Single Stage ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Stability ◽  
Length Coverage

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

scholarly journals Dynamics of Single Droplet Splashing on Liquid Film by Coupling FVM with VOF

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 841
Author(s):  
Yuzhen Jin ◽  
Huang Zhou ◽  
Linhang Zhu ◽  
Zeqing Li
Keyword(s):  
Liquid Film ◽  
Weber Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Single Droplet ◽  
Navier Stokes Equations ◽  
Volume Method ◽  
The Relationship

A three-dimensional numerical study of a single droplet splashing vertically on a liquid film is presented. The numerical method is based on the finite volume method (FVM) of Navier–Stokes equations coupled with the volume of fluid (VOF) method, and the adaptive local mesh refinement technology is adopted. It enables the liquid–gas interface to be tracked more accurately, and to be less computationally expensive. The relationship between the diameter of the free rim, the height of the crown with different numbers of collision Weber, and the thickness of the liquid film is explored. The results indicate that the crown height increases as the Weber number increases, and the diameter of the crown rim is inversely proportional to the collision Weber number. It can also be concluded that the dimensionless height of the crown decreases with the increase in the thickness of the dimensionless liquid film, which has little effect on the diameter of the crown rim during its growth.

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