Numerical and Experimental Assessment of a Linear Aerospike

In the present work a linear aerospike nozzle model has been studied with cold flow experiments in various working conditions. A series of numerical 3D RANS simulations have been performed in order to directly compare numerical and experimental results. Mean pressure distributions have been measured on the nozzle model symmetry plane, in order to characterize the flow evolution along the walls of the plug. The presented results show a good agreement between numerical and experimental results

Proportional Opposition Control of Turbulence

Proportional opposition control of sweep events in a turbulent boundary layer has been carried out using a wall-normal jet. Changes to the turbulence structure in the region closer to the wall have been examined using hot-wire anemometry. Control of each detected sweep event has been obtained by using multiple injections whose number is proportional to the duration of the event. Differently from the more conventional opposition control technique with a single injection of a longer duration, the proposed technique with multiple injections allows to control the sweep event over its whole duration without changing the working parameters of the jet actuator

On the Sensor Placement for Flow Field Estimations

PIV09-002

On the Near Field of an Axisymmetric Synthetic Jet

The axisymmetric synthetic jet produced by an oscillating piston has been investigated experimentally. The study was performed in water using digital particle image velocimetry for the instantaneous velocity planar measurements. The near field, up to x/d0 ≈ 6, was investigated for three different Reynolds numbers. The self-similarity of the flow field is already fully reached for the mean velocity profiles at x/d0 ≈ 4 while longer distances are needed for the turbulent intensity profiles. The flow structure investigation shows that a single vortex ring or a train of vortex rings characterizes the near field during the blowing phase, depending on the jet flow parameters. The details of the flow field have also been described in terms of phase-averaged flow analysis and of triple decomposition of the instantaneous velocity field. The near flow fields investigated do not seem to be influenced by the Reynolds number

Opposition control of sweep events in a turbulent boundary layer

Proportional opposition control of sweep events in a turbulent boundary layer has been carried out using a wall-normal jet. Hot-wire anemometry has been used in order to observe the changes to the turbulence structure in the region closer to the wall. Control of each detected sweep event has been obtained by using multiple injections whose number is proportional to the duration of the event. The proposed technique with multiple injections allows to control the sweep event over its whole duration without changing the working parameters of the jet actuato

Characteristics of the flow around a superhydrophobic obstacle

The flow around a partially buried circular cylinder on a smooth plane boundary is studied using Particle Image Velocimetry. The cylinder axis is perpendicular to the incoming flow. The burial ratio B/D is equal to 0.5 , where B is the burial depth and D is the diameter of the cylinder. The ratio between the span of the obstacle and its diameter is equal to 11.7 . The flow is considered nominally two-dimensional. The case in which the obstacle is coated with a random-textured superhydrophobic surface is compared with the case of a smooth surface. In the superhydrophobic case the surface was prepared by using a double layer spray coating method (NeverWet solution). An extreme contact angle of about 165° was evaluated. Measurements were carried out in a closed-loop water tunnel for a Reynolds number, based on the cylinder diameter and on the incoming flow velocity Ue , of about 360. The incoming boundary layer is laminar and the boundary layer thickness, in absence of the obstacle, is of the same order of the obstacle height. The present research is related to the understanding of the role of slip conditions in presence of pressure gradients in order to provide useful information for flow control strategy