Effects of a trapped vortex cell on thick wing profile

Experimental investigation on the effects originated from a trapped vortex cell on the NACA0024 airfoi

Aerodynamic drag reduction by means of platooning configurations of light commercial vehicles: A flow field analysis

Platooning configurations of two, three and four commercial vehicles were tested at a Reynolds number based on the vehicle’s length () of. The platoon configurations were obtained using an instrumented model, and three wooden replicas located at different positions with respect to the instrumented one. The reference model presents a slant angle at the leading edge, which can produce, in principle, a significantly different flow field compared to the generally studied Ahmed body. Drag, static pressure distributions and pressure fluctuations measurements were carried out. Additionally, planar PIV measurements were performed to investigate the near wake of the two-vehicles platoon configuration. For the two-models platoon, drag reductions of 30% and 43% were evidenced for the front and for the rear vehicle, respectively, at an inter-vehicle distance () equal to half the vehicle’s length, and corresponding to an average drag reduction of 36.5%. For increasing distance, the benefit associated with the platooning configuration reduces, reaching an average drag reduction of 20% at = 3. We relate the vehicle’s drag to the flow field organization and to the distribution of the modal energy through Proper Orthogonal Decomposition of the microphonic probes located on the base of the instrumented vehicle. We also evidence that the key element that is responsible for the pumping of the wake is the large vortex that generates near the top edge of the vehicle’s base. We show that the slant angle does not affect the drag reduction of the leading vehicle of the platoon, whereas it can lead to larger differences in the case of the rear vehicle. For three and four-vehicles platoons, consistently larger values of the average drag reduction are experienced (35%) and were also obtained for distances >1. A simple model describing the overall drag reduction for a generic number of vehicles is presented and discussed

Bluff Body Flow Control Through Piezoelectric Actuators

Delay separation from bluff bodies leads to drag reduction. An active flow control technique based on piezoelectric actuators has been arranged on a 2D cilynder in subsonic flow. Experimental investigation in precritical and postcritical conditions of the flow has been conducted varying the configurations of the actuators. Drag reduction up to 10% without a complete optimization of the flow control parameters have been obtained

Transitional regime control in a fully developed channel flow

Friction drag reduction is one of the main topic of investigation because of the great beneficial fallout in different engineering field. Laminar transition can be efficiently controlled using suitable flow control techniques [1]. Recent studies focused on the possibility of controlling transitional regimes in wall bounded flow have shown that the generation of streaks with appropriate intensity are able to control the transition in boundary layer. The concept of such control was shown by A1 et al. [2] using small cylinder mounted in the spanwise direction of a flat plate a zero incidence. These devices were able to generate streamwise vortices that in turn gave rise to streaks of well specific amplitude able to attenuate the transition. The paper will present results of an experimental investigation related to the transition control in a fully developed channel flow. For the streaks generation couples of convergent jets are positioned in the spanwise direction. In figure 1 the channel with the injection system are shown

Trapped vortex cell for aeronautical applications: flow analysis through PIV and Wavelet transform tools

Results of the application of a trapped vortex cell to an airfoil with the aim of improving the aerodynamic performances are presented for two complementary experiments arranged at CIRA and at Politecnico di Torino. In the CIRA experiments, PIV measurements on a simplified configuration were carried out to characterize the trapped vortical structure and its effect on the separating flow downstream of the cell. In the experimental investigation at Politecnico di Torino, static pressure distributions were measured around a complete airfoil model, to yield lift and pitching moment coefficients. Wake surveys were also carried out to measure the drag. To study the unsteady phenomena inside the cavity pressure fluctuations signals were also investigated using Kulite sensors. In both experiments, the angle of attack of the airfoil and the Reynolds number were varied. It is shown that the flow inside the cell is highly unsteady with significant shedding of flow structures downstream. This phenomenon results in a large region of separated flow, in higher drag and lower lift. By contrast, the cell flow is considerably stabilized and regularized by applying distributed suction over the cell wall. As a result, the flow downstream of the cell reattaches and lower drag and larger lift are observed

Friction drag measurements in turbulent wall flows

Results of an experimental investigation devoted to the assessment of methodologies aimed at the friction drag measurement in turbulent wall flows are presented. Two techniques for local measurements have been developed. Namely, different versions of the velocity profile method have been used for a turbulent boundary layer developing on a flat plate. The oil flow interferometer has been arranged and results related with measurements performed in a fully developed turbulent channel flow and in the turbulent boundary layer are presented. Moreover a balance based on a floating-buoyancy system finalized to the integral measurement of the friction force acting on the flat plate is presented. The results of the three techniques are compared considering as a reference a well assessed empirical law. Good level of measurement accuracy using the balance has been evidenced highlighting the capability of the balance or the characterization of micro-grooved surfaces addressed for friction drag reduction applications

Multi-time delay, multi-point Linear Stochastic Estimation of a cavity shear layer velocity from wall-pressure measurements

Multi-time-delay Linear Stochastic Estimation (MTD-LSE) technique is thoroughly described, focusing on its fundamental properties and potentialities. In the multi-time-delay ap- proach, the estimate of the temporal evolution of the velocity at a given location in the flow field is obtained from multiple past samples of the unconditional sources. The technique is applied to estimate the velocity in a cavity shear layer flow, based on wall-pressure measurements from multiple sensor