China
Africa
Explore chapters and articles related to this topic
Force and Moment Analysis
Published in George Emanuel, Analytical Fluid Dynamics, 2017
In the lift equation, the ρuw term represents the downwash when w is negative. Downwash, of course, contributes a positive lift force. There is a coupling between drag and the lift through the p + ρu2 and ρuw terms. This coupling is referred to as lift‐induced drag. A positive lift can be generated by the unsteady term, as caused, for example, by an oscillating wing. For this, asymmetry inside the CV in the z direction is required. This type of lift is also coupled to the drag, since ∂(ρw→)/∂t $ \partial (\rho \vec{w})/\partial t $
Vorticity Confinement Applied to Accurate Prediction of Convection of Wing Tip Vortices and Induced Drag
Published in International Journal of Computational Fluid Dynamics, 2021
Alex Povitsky, Kristopher C. Pierson
This study aims to achieve a reliable prediction of lift-induced drag (or simply, induced drag), which is associated with the formation and convection of tip vortices shed by wings, and to minimise numerical dissipation of tip vortices by adopting vorticity confinement (VC) method. The goal was to improve the accuracy of vorticity confinement approach using moderate amount of computational resources and avoid possible over-confinement by combining the VC with total variation diminishing (TVD) approach. The recent study by the authors (Povitsky and Pierson 2020) was limited to 2-D vortices, which were moving in uniform flow, while the current study extended the approach to accurate modelling of vortices shed by stationary and rotating wings and convected by 3-D non-uniform flow behind wings. The method can be used in winglet design optimisation to reduce the strength of tip vortices. The approach will assist in design lift- and thrust- generating air vehicular systems that may include stationary, flapping and rotating wings, and propellers.
Combined Vorticity Confinement and TVD Approaches for Accurate Vortex Modelling
Published in International Journal of Computational Fluid Dynamics, 2020
Alex Povitsky, Kristopher C. Pierson
In the separate recent study by the authors (Pierson and Povitsky 2020), the proposed combined TVD and VC technique was applied to accurate modelling of convection of tip vortices shed by (i) a 3-D stationary wing and (ii) rotating wing using combinations of structured and unstructured grids with variable grid steps. For stationary wing, the 3-D inviscid simulations were post-processed using the wake-integral technique to determine lift-induced drag force. For rotating wing, the VC approach was combined with the Reynolds stress turbulence model, and the results were compared to experimental data of tip vortex evolution to show improved accuracy of the proposed approach for long-scale simulations of convected vortex shed by the tip of rotating blade important for the rotorcraft industry.
RANS simulation of the tip vortex flow generated around a NACA 0015 hydrofoil and examination of its hydrodynamic characteristics
Published in Journal of Marine Engineering & Technology, 2018
Parviz Ghadimi, Araz Tanha, Sasan Tavakoli, Mohammad A. Feizi Chekab
Various numerical and experimental methods have been applied by different researchers for exploring the vortex generation at the tip of aerofoils (Lambard et al. 2015) and hydrofoils (Briggs et al. 2014; Dreyer et al. 2014). To begin with, some important experimental works are reviewed. One of the earliest experimental works in this field was conducted by Brich et al. (2004) in which they concentrated on the generated tip vortex around a NACA 0015 hydrofoil. They measured the lift-induced drag and consequently argued that the maximum size of the vortex can be seen right behind the tip. Brich and Lee (2005) later extended their research and preformed similar studies on a NACA 0015 foil having a flap at its tip and observed that vortices become more concentrated when a flap is used at the trailing edge of the foil. Ramaprian and Zheng (1997) performed a different experimental study in which they used laser Doppler velocimetry (LDV). They reported the rollup of a tip vortex and showed that vortex becomes axisymmetric at two chord lengths downstream of the trailing edge. Boulon et al. (1999) also used LDV in order to study the tip vortices generated near an elliptical hydrofoil. They tried to clarify how a flat plate which is perpendicular to the span may reduce the negative effects of the tip vortices and consequently affect the cavitation phenomenon. Moreover, they discussed how clearance of the tip vortex can benefit the surface by omitting the cavitation. In addition to the mentioned experimental methods, optical-velocimetry may be considered as another effective and accurate method which can help us understand the generated vortices around a foil. This approach was adopted Grant et al. (2006), who investigated the tip vortices generated near a foil.