Valentina Motta

Three-dimensional simulation of a complete Vertical Axis Wind Turbine using overlapping grids

Abstract Three-dimensional simulations of the aerodynamic field around a three-blade straight-axis Vertical Axis Wind Turbine (VAWT) are presented for two values of the Tip Speed Ratio λ (TSR), namely λ = 1.52 and λ = 2.5 . Numerical simulations were carried out using the over-set grid solver ROSITA (ROtorcraft Software ITAly). The Reynolds-Averaged Navier–Stokes equations are completed by the Spalart–Allmaras turbulence model. A strong interaction between the blade and the blade wakes is evidenced. Dynamic stall is observed in the case λ = 2.5 . The computed flow-field presents diverse three-dimensional effects, including the interaction between the blades and the tip vortices and the aerodynamic disturbances from the turbine shaft and the support arms. Three-dimensional effects are more relevant for λ = 2.5 . The comparison to experimental data confirms the general features of the flow.

Linear Reduced-Order Model for Unsteady Aerodynamics of an L-Shaped Gurney Flap

The purpose of the work is to investigate the mechanism that underlies the development of unsteady loads by a novel L-shaped Gurney flap conceived to perform vibration control on rotorcraft blades. The device is combination of a spoiler with a Gurney flap. Exploiting the capabilities of a Reynolds-averaged Navier–Stokes flow solver employing the overset mesh approach, several numerical simulations are carried out at low Mach number. These simulations are used to develop a physically based linear reduced-order model in the frequency domain for the unsteady lift and pitching moment of a NACA 0012 airfoil, considering as input the pitch and plunge harmonic oscillations of the airfoil, together with the oscillations of the L-shaped Gurney flap. The aerodynamic assessment of the L-tab shows that the behavior of the loads can be predicted using an equivalent flat-plate model to represent the airfoil composed by three segments: the first representing the fixed part of the airfoil, the second representing the lon...

Numerical assessment of an L-shaped Gurney flap for load control

The aerodynamic performance of a novel trailing edge L-shaped flap design is characterized numerically by means of computational fluid dynamics. The device is primarily thought for aerodynamic load adaptation to flight conditions. The device could be applied on a broad range of flying vehicles, like rotorcraft, for which it has been primarily designed, and also fixed wing aircraft and wind turbines. The operation of this movable surface is twofold. On one side, when the device is deployed downward, it acts as a Gurney flap, allowing the increase of the aerodynamic lift, without severe drawbacks in terms of drag rise. On the other side, when it is deflected upward, it is found capable to significantly alleviate the negative effects of stall. Simulations are carried out on a NACA 0012 airfoil equipped with the present L-shaped device at several angles of attack, both in linear and stall regimes. The reliability of numerical computations is supported by comparisons with pressure measurements and PIV surveys. Moreover, for small angles of attack, a Mach sensitivity analysis is performed, to assess the effects of compressibility on the L-shaped flap. Additionally, this work highlights how such device, when designed appropriately, can even delay the static stall onset.

A low Speed Compressor Test Rig for Flutter Investigations

ABSTRACT A test facility for aereolastic investigations has been installed at the chair of Aero Engines at the Technische Universit¨at Berlin.The test rig provides data for tool and code validation and is used for basic aeroelastic experiments. It is a low speed wind tunnel which allows free and controlled flutter testing. The test section contains a linear cascade with eleven compressor blades. Nine of them are elastically suspended. The paper presents a detailed description of the test facility, results to evaluate the overall flow quality and an aeroelastic model to predict the flutter velocity and critical interblade phase angles. Hot-wire anemometry has been applied to examine the inlet flow for several Mach- and Reynolds numbers. The results show small turbulence intensities. The blade surface pressure distribution and the flow field of the blade’s suction and pressure side has been accessed by oil flow visualization.