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The applicability of ow control by periodic blowing and suction through a slot in a spatially evolving Stratford ramp ow is investigated by numerical simulations based on the two{dimensional incom-pressible Navier-Stokes equations. The simulations have shown that beyond certain Reynolds numbers, instability waves are developing even when no \con-trolled"… (More)

- A. Gross, H. F. Fasel, M. J. Kloker
- 2010

We carried out direct numerical simulations of the flow past a two-dimensional S822 wind turbine blade section at a chord Reynolds number of Re=100,000 and an angle of attack of α = 5deg. Without blade rotation the separated boundary layer " rolls up " into spanwise vortices which then " break up " into smaller scale structures leading to transition to… (More)

The lack of understanding of most of the relevant physical mechanisms when applying flow control limits the prospects of successfully transitioning flow-control technologies into real flight vehicles. Successful control of boundary-layer separation for lifting surfaces promises major performance gains especially when large laminar runs are desired in order… (More)

Flow separation is always three-dimensional despite the fact that most of the past research has focused on two-dimensional separation. The three-dimensional character of separation is particularly relevant when low-aspect ratio geometries are considered. Separation is often associated with unsteadiness, which is caused by large coherent structures that are… (More)

Flow separation from lifting surfaces such as airfoils is undesirable as it deteriorates performance. For example, when airfoils that are designed for large Reynolds numbers are operated at smaller off-design Reynolds numbers, laminar separation can occur. Laminar separation typically leads to transition and reattachment. Transition is influenced by… (More)

For Navy relevant geometries, separation of wall bounded flows is a highly complex phenomenon. Because of the relatively high Reynolds numbers involved,separation is always associated with considerable unsteadiness. This unsteadiness is caused by large coherent structures that are a consequence of hydrodynamic instability mechanisms of the mean flow. In… (More)

A numerical method is presented for Direct Numerical Simulations (DNS) of a turbulent boundary layer ow over a curved wall. The incompress-ible, unsteady Navier-Stokes equations in vorticity-velocity formulation and curvilinear coordinates are solved using compact diierences of fourth order accuracy and a fourth-order Runge-Kutta method. The resulting DNS… (More)

Operating low-pressure turbines (LPT) at off-design conditions or considering more aggressive designs can lead to laminar separation on the suction side of the LPT blades resulting in significant turbine and overall engine performance losses. In these instances, performance improvements may be achieved with active flow control (AFC). In an extensive… (More)

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