Vortex Generators (VGs) are one of the most commonly used passive flow control devices. Recent studies have shown that it is beneficial to use sub-boundary layer vortex generators (SBVGs). The height of these generators varies between 10% - 50% of the boundary layer thickness. However, the reduced height causes the induced vortices to be substantially weaker. Therefore, using SBVG is beneficial only when the regions of flow separation are well defined. To better understand and comprehensively predict the effectiveness of these devices for flow control over a range of operating conditions, two different SBVG profile: rectangular vortex generators (RVGs) and triangular vortex generators (TVGs) are analysed when subjected to a laminar boundary layer. The topics of interest are instantaneous flow, mean flow, far-field acoustic properties and influence of the angle of attack on the VG vane. The results emphasise the unsteady nature of the induced vortices for both the VG profiles. For RVGs, mean flow visualisation indicates the presence of local re-circulation zones in between the vanes with an increase in angle of attack. Additionally, secondary vortices are noted for both the VGs. These secondary vortices significantly influence the properties of the primary vortices thereby, suggesting that, effectively managing the secondary vortices using suitable design changes to VG profile could be one of the possible ways to accomplish better flow control.

One of the most commonly used flow control techniques to trim the aerodynamic performance of wind turbine blades are vortex generators. This passive device, which does not require any active energy, is gaining an increasing interest in this sector especially due to the trend of increasing wind turbine size. Vortex generators are a flow control technique used to prevent or at least lessen the severity of flow separation. The streamwise vortices shed at the free tips of the vortex generators increase the mixing between the high-energy flow in the outer part of the boundary-layer with the low energy regions near the walls. The shed vortices are defined by the strength of the vortices just downstream of the device, the streamwise decay of the vortex strength and the vortex trajectory. In order to assess and optimise the use of vortex generators, there is a need to accurately model the effect of this device in a cost and time efficient way. This could be achieved by modelling vortex generators using integral boundary-layer codes. XFOIL and RFOIL are two well-known integral boundary-layer codes. These two codes rely on Prandtl’s theory stating that a flow field around an object can be divided into two areas: the inviscid outer flow and the viscid inner flow. The inviscid part of the flow is solved using a streamfunction panel method while the viscid boundary-layer solution is prescribed by the boundary-layer equations and additional closure relations. Both solutions are strongly interconnected to each other. A suitable methodology to model the effect of vortex generators into integral boundary-layer codes is the source term approach. This approach was already initiated by Kerho and Kramer1 but is revised carefully in this thesis. The introduction of the streamwise vortices results in an increase in dissipation. To simulate this, the shear-lag equation is modified by introducing an additional source term to the equilibrium shear stress coefficient. The strength of this additional source term is varied over the chord to mimic the downstream decay of the shed vortex circulation. Implementing the source term into XFOIL and RFOIL allows to capture the expected effect of vortex generators on the boundary-layer properties. The source term shape function is prescribed by three parameters: the source term strength, the decay rate and the location of the vortex generators. Because the source term depends on the vortex generator geometry and the local flow properties, its value is calibrated for different airfoil/vortex generator configurations using reference data. Afterwards, these calibrated source terms are related back to the vortex generator parameters and local boundary-layer properties to establish an empirical relation for the source term integral. To do so, a multiple variable linear regression is applied in which the independent variables are the vortex generator height, vortex generator length, inflow angle, local boundary-layer momentum thickness and edge velocity. The source term empirical relation is implemented in XFOIL and RFOIL. Implementing the source term empirical relation led to the development of the foundations of the design tools XFOILVG and RFOILVG. These two codes are extensively validated to evaluate the performance and identify code limitations. Validating the source term empirical relation and its implementation, is realised by comparing the codes’ predictions with reference data from the data base that was already used to set up the source term relation. To further validate the robustness and generality of the code with respect to airfoil selection and Reynolds number, external data sets adopted from literature are used. Based on the validation results, it is believed that the source term approach to model vortex generators within the integral boundary-layer theory is very promising. To further elaborate on this method, recommendations for further work are made. These recommendations concern the data base used to set up the source term empirical relation, the effect of vortex generators on the friction coefficient and the role and value of adding a transition model.

The continued grow of the wind industry has resulted in an increase in turbine cluster density in wind farms. This has made the topic of wind turbine and wind farm wake aerodynamics more relevant than ever. Wind turbine wake models are used to predict the deficit and recovery of the wind velocities in the wake. The currently used wake models in the industry contain a relatively simple approach to model the near-wake of the turbine, assuming an initial hat or Gaussian deficit profile at a fixed location in the wake. This thesis presents an alternative near-wake model based on discrete, inviscid, perfectly circular vortex rings for use in conjuncture with existing far-wake models.