The Leishman–Beddoes dynamic stall model is a popular model that has been widely applied in both helicopter and wind turbine aerodynamics. This model has been specially refined and tuned for helicopter applications, where the Mach number is usually above 0.3. However, experimental results and analyses at the University of Glasgow have suggested that the original Leishman–Beddoes model reconstructs the unsteady airloads at low Mach numbers less well than at higher Mach numbers. This is particularly so for stall onset and the return from the fully stalled state. In this paper, a modified dynamic stall model that adapts the Leishman–Beddoes dynamic stall model for lower Mach numbers is proposed. The main modifications include a new stall-onset indication, a new return modeling from stalled state, a revised chordwise force, and dynamic vortex modeling. The comparisons to the Glasgow University dynamic stall database showed that the modified model is capable of giving improved reconstructions of unsteady aerofoil data in low Mach numbers.

The Beddoes/Leishman dynamic-stall model has become one of the most popular for the provision of unsteady aerofoil data embedded in much larger codes. The underlying modelling philosophy was that it should be based on the best understanding, or description, of the associated physical phenomena. Even although the model was guided by the flow physics, it requires significant empirical inputs in the formThese conditions are normally associated with pitching and plunging motions and were initially of much interest to helicopter rotor-aerodynamicists, who required an assessment of rotor loads during forward and manoeuvring flight. Today, dynamic stall is also relevant to the performance and durability of wind turbines.Carr [4] gives an illustration for the events of a dynamic stall process, for an aerofoil undergoing a sinusoidal pitch profile, shown in Figure 1. Chronologically, the dynamic stall events start at point (a), where the pitching aerofoil passes the staticstall angle of attack, but without any discernible change in the flow around the airfoil, and the flow remains fully attached.Then the flow reverses near the surface at the trailing edge region starting at point (b), but still with no large separation due to the dynamic effects. This reversal moves up the chord until it covers most of the aerofoil, at which stages ((c) and (d)) the leading edge flow no longer remains attached and a strong vortical flow develops (point (e)). As the vortex enlarges and remains close to the leading edge, there is an obvious increase in the lift-curve slope at (f) and associated vortically induced normal force coefficient, N C , ((g) and (h)). The vortex subsequently convects downstream and finally detaches from the trailing edge, inducing a strong nose-down pitching moment at (i). After that, when the flow over the aerofoil upper surface is fully separated, the lift break (lift stall) occurs (j). As the angle of attack decreases continuously, the reattachment process takes place. According to Niven et al [5], at some angle of attack (close to the static fully-stalled state), the leading edge reattachment occurs. This is characterised by two distinct but related events. First, all the large eddies, due to the stall, are convected over the chord and into the free stream at constant speed and, second, following closely behind is the reestablishment of a fully attached boundary layer. The convective component, i.e. the first, normally takes a few chord lengths of free-stream travel, at which point the lift reaches its lowest value. Then the flow transits to a fully attached state at the end of stage (k). Obviously, the whole process forms a large hysteresis loop, shown in figure 1, which is taken from Carr et al.[6].Leishman [7] explores the flow topology of dynamic stall and summarises that the aerofoil dynamic behaviour is significantly different from the steady case in following three aspects:-Under dynamic conditions, since the circulation is shed into the wake at the trailing edge of the aerofoil, the induced un...

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The International Energy Agency Technology Collaboration Programme for Ocean Energy Systems (OES) initiated the OES Wave Energy Conversion Modelling Task, which focused on the verification and validation of numerical models for simulating wave energy converters (WECs). The long-term goal is to assess the accuracy of and establish confidence in the use of numerical models used in design as well as power performance assessment of WECs. To establish this confidence, the authors used different existing computational modelling tools to simulate given tasks to identify uncertainties related to simulation methodologies: (i) linear potential flow methods; (ii) weakly nonlinear Froude–Krylov methods; and (iii) fully nonlinear methods (fully nonlinear potential flow and Navier–Stokes models). This article summarizes the code-to-code task and code-to-experiment task that have been performed so far in this project, with a focus on investigating the impact of different levels of nonlinearities in the numerical models. Two different WECs were studied and simulated. The first was a heaving semi-submerged sphere, where free-decay tests and both regular and irregular wave cases were investigated in a code-to-code comparison. The second case was a heaving float corresponding to a physical model tested in a wave tank. We considered radiation, diffraction, and regular wave cases and compared quantities, such as the WEC motion, power output and hydrodynamic loading.

This is an investigation on the development of a numerical assessment method for the hydrodynamic performance of an oscillating water column (OWC) wave energy converter. In the research work, a systematic study has been carried out on how the hydrodynamic problem can be solved and represented reliably, focusing on the phenomena of the interactions of the wave-structure and the wave-internal water surface. These phenomena are extensively examined numerically to show how the hydrodynamic parameters can be reliably obtained and used for the OWC performance assessment. In studying the dynamic system, a two-body system is used for the OWC wave energy converter. The first body is the device itself, and the second body is an imaginary “piston,” which replaces part of the water at the internal water surface in the water column. One advantage of the two-body system for an OWC wave energy converter is its physical representations, and therefore, the relevant mathematical expressions and the numerical simulation can be straightforward. That is, the main hydrodynamic parameters can be assessed using the boundary element method of the potential flow in frequency domain, and the relevant parameters are transformed directly from frequency domain to time domain for the two-body system. However, as it is shown in the research, an appropriate representation of the “imaginary” piston is very important, especially when the relevant parameters have to be transformed from frequency-domain to time domain for a further analysis. The examples given in the research have shown that the correct parameters transformed from frequency domain to time domain can be a vital factor for a successful numerical simulation