Simulation of unsteady turbulent flows around moving aerofoils using the pseudo-time method

SUMMARYResults are reported of an unsteady Reynolds-averaged Navier -Stokes (RANS) method for simulation of the boundary layer and wake and wave field for a surface ship advancing in regular head waves, but restrained from body motions. Second-order finite differences are used for both spatial and temporal discretization and a Poisson equation projection method is used for velocity -pressure coupling. The exact kinematic free-surface boundary condition is solved for the free-surface elevation using a body-fitted/freesurface conforming grid updated in each time step. The simulations are for the model problem of a Wigley hull advancing in calm water and in regular head waves. Verification and validation procedures are followed, which include careful consideration of both simulation and experimental uncertainties. The steady flow results are comparable to other steady RANS methods in predicting resistance, boundary layer and wake, and free-surface effects. The unsteady flow results cover a wide range of Froude number, wavelength, and amplitude for which first harmonic amplitude and phase force and moment experimental data are available for validation along with frequency domain, linear potential flow results for comparisons. The present results, which include the effects of turbulent flow and non-linear interactions, are in good agreement with the data and overall show better capability than the potential flow results. The physics of the unsteady boundary layer and wake and wave field response are explained with regard to frequency of encounter and seakeeping theory. The results of the present study suggest applicability for additional complexities such as practical ship geometry, ship motion, and maneuvering in arbitrary ambient waves.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unsteady RANS method for surface ship boundary layer and wake and wave field

Rhee

Stern

2001

“…In spite of this, since one is often concerned with only mean ow quantities and steady owÿelds are less computationally demanding, unsteady ow simulations have historically been more rare. Contemporary computer resources now render three-dimensional unsteady owÿeld computation viable [1]. As these simulations consume vast computational resources, their e ciency is of great importance.…”

Section: Introductionmentioning

confidence: 99%

Iterative solution techniques for unsteady flow computations using higher order time integration schemes

Bijl

Carpenter

2005

Computational study of unsteady turbulent flows around oscillating and ramping aerofoils

Barakos

Drikakis

2003

SUMMARYThe aim of this work is to computationally investigate subsonic and transonic turbulent ows around oscillating and ramping aerofoils under dynamic-stall conditions. The investigation is based on a highresolution Godunov-type method and several turbulence closures. The Navier-Stokes and turbulence transport equations are solved in a strongly coupled fashion via an implicit-unfactored scheme. We present results from several computations of ows around oscillating and ramping aerofoils at various conditions in order to (i) assess the accuracy of di erent turbulence models and (ii) contribute towards a better understanding of dynamic-stall ows. The results show that the employed non-linear eddyviscosity model generally improves the accuracy of the computations compared to linear models, but at low incidence angles the Spalart-Allmaras one-equation model was found to provide adequate results. Further, the computations reveal strong similarities between laminar and high-Reynolds number dynamicstall ows as well as between ramping and oscillating aerofoil cases. Investigation of the Mach number e ects on dynamic-stall reveals a delay of the stall angle within a range of Mach numbers. Investigation of the reduced frequency e ects suggests the existence of an (almost) linear variation between pitch rate and stall angle, with higher slope at lower pitch rates. The pitch rate a ects both the onset of dynamic-stall as well as the evolution of the associated vortical structures.