The aerodynamic interference between oscillating models and the walls of slotted windtunnels is controlled by the homogeneous wall boundary condition, which has hitherto been uncertain. In this report a new homogeneous boundary condition for slotted tunnels is suggested which incorporates the important effects of plenum chamber depth and slot parameter.

In particular, this new boundary condition controls the transverse resonance frequencies of the tunnel, which represent a severe form of wall interference. Hence a comparison of measured resonance frequencies with predictions based on such a boundary condition provides a good test of its correctness.

The new homogeneous boundary condition complements that obtained previously for a perforated tunnel and is essentially similar in character. The boundary condition is applicable to oscillatory flows at frequencies ranging from quasi-steady values to multiples of the first resonance frequency.

The flow structure on the upper side of a delta wing is extremely complex. At moderate angle of attack the flowfield is dominated by organised vortical flow structures emanating from the leading edge. The pressure distribution created on the wing surface by these leading edge vortices causes an increment of lift which may be a relevant percentage of the total wing lift, depending on sweep angle.

Delta wing performance is conditioned, however, by a phenomenon known as vortex breakdown or vortex bursting which appears at high angle of attack. This leads to a drastic change in the flowfield which influences the trend of the aerodynamic coefficients.

With the aim of giving a contribution to the understanding of the phenomenon of vortex breakdown, a 65° delta wing has been extensively tested in the low speed windtunnel of Politecnico di Torino (TPI) both in static and dynamic conditions, under forced oscillatory motions.

Many experiments have been carried out in an effort to understand the factors which can affect the breakdown by varying angle of attack, sideslip angle and Reynolds number.

Flow visualizations have been performed using helium bubble tracers. This technique showed a very good capability for visualizing vortical flows and breakdown, both in static and dynamic conditions.

For the static case, pressure distributions are presented, correlated to force measurements and flow visualizations, at different angles of attack and sideslip for different flow conditions.

For the dynamic case force measurements are shown, compared with flow visualizations, for different angles of attack and for different oscillation frequencies.

Previous experimental studies have shown that the development of flow behind the trailing edge of a lobed forced mixer is greatly influenced by the formation of large-scale streamwise vortices. The main objective of the present study is to establish quantitatively the presence and role of the streamwise vortices in the mixing layer in the near field of a lobed forced mixer trailing edge. The near field was defined as the region within five wavelengths (of the trailing edge profile) from the trailing edge. A two-stream mixing layer with a velocity ratio of 0.6 was generated with initially turbulent boundary layers and nominally two-dimensional flow. Mean flow and turbulence measurements were made on fine cross-plane grids across the wake region and at several streamwise locations using a two-component laser-doppler anemometer. Production of turbulent kinetic energy existed in most parts of the near field enhancing the overall mixing process. The streamwise vortex development underwent a three-step process by which it was formed, intensified and quickly dissipated towards the end of the near field. The distance between two rows of streamwise vortices of alternate signs within a lobe reduced with downstream distance causing the amalgamation and annihilation of the vortices. Analysing this movement of vortices, based on inviscid vortex dynamics, suggested that the normal vortices shed at the trailing edge had actually provided a squeezing (pinched off) effect to two adjacent rows of streamwise vortices within a lobe, forcing them to interact with each other.

Two-dimensional Euler equations are solved on unstructured triangular meshes using commonly available minicomputers. The driving algorithm is an upwind biased implicit cell-centred finite volume scheme. The spatial discretisation involves a naturally dissipative flux-split approach that sharply captures Shockwaves. The grid generation method uses a type of advancing front technique which triangulates a given set of points. To demonstrate the application, the steady flow results are presented for single and two component aerofoils. The unsteady results are obtained using a dynamic mesh algorithm for an aerofoil pitching harmonically about the quarter chord. The paper presents a description of the grid generation and movement algorithm and of the Euler solver, along with results and comparison that assess their capabilities.