Particle image velocimetry (PIV) measurements at relatively low Reynolds numbers in a turbulent boundary layer over a three-dimensional roughened surface, consisting of pyramidal rows, have been presented. Measurements have been taken in a streamwise wall-normal plane intercepting the apex of a row of pyramids and the diagonal of the square base. The results shown in this paper point out the non-homogeneity of the flow in the roughness sub-layer. The different flow behaviour along the ascendant and the descendent part of the pyramids and in the region between two consecutive pyramids has been visualised. Low values of the streamwise component of the mean velocity and high values of the streamwise and wall-normal component of the Reynolds normal stresses, turbulent kinetic energy and Reynolds shear stresses are present in the downstream part of the pyramids, near their base. The mean representation of the flow shows swirling patterns in correspondence of the top of the pyramids. It is suggested that this representation is produced mainly by vortical structures travelling along the wall, retarded and intensified when interacting with the flow around the roughness element and by swirling patterns originating from the interaction of the incoming flow with the pyramids. In order to understand the origin of the high turbulence activity observed downstream the pyramids, near their base, a conditional analysis based on the quadrant method has been performed. It has been shown that sweep events are the major contributor to the very high values of the Reynolds shear stresses observed in this region and are due to the combination of the vortical flow at the top of the pyramid and a large scale (with respect to the roughness element) inflow motion.

The work focuses on the characterization of the flowfield over a truncated linear aerospike by combining theoretical grounds, numerical simulations and experimental tests. The experimental investigations are carried out on a test rig designed at Politecnico di Torino for advanced nozzle testing. Fully three-dimensional CFD analyses are performed on the actual geometry of the experimental nozzle model. At low nozzle pressure ratios (nprs) the analysis combines numerical simulations and experimental testing, which are also used for validating the CFD results. At higher nprs, the flowfield characterization is performed only by three-dimensional CFD analyses. In addition to the validation of the numerical method, the edge effects at different nprs have been observed.

The paper describes the design, development and testing of an automated, programmable pressure measurement system based on low-cost sensors. To improve the accuracy of the measure, multiple sensors with different pressure range are used. A micro-controller drives the automatic switching logic and activates the suitable sensor for the measured pressure range. A practical application is described, where the device measures the velocity profile at the inlet of a micro-jetengine and computes the instantaneous inlet mass-flow rate.

The performances of two linear aerospike nozzles, generated by truncating the same plug contour at 40% and 20% of its ideal length, are investigated numerically within a two-dimensional approximation and compared with each other. The nozzle geometry is a 2D representation, extracted from the CAD model of the actual nozzles under experimental investigation. In the working conditions studied here, the nozzle is throttled differentially, by setting different flow conditions on the upper and lower inlet, with the aim of generating thrust vectoring effects. The performances and flowfield of both aerospikes are investigated for values of the nozzle pressure ratio (npr) ranging from 3.7 up to the design condition ($\mathrm{NPR}=200$), and for several levels of differential throttling. The CFD approach adopted is based on a two-dimensional RANS flow model. Comparisons between the numerical and experimental data are performed at two nozzle working conditions: without and with differential throttling. The numerical results are in good agreement with the experimental data. Moreover, the numerical simulations of the throttling case have shown a thrust deflection of about 5 degrees, with a differential pressure of approximately 10 percent.

This study investigates the use of a feed-forward neural network (FNN) and a hybrid approach combining an FNN with proper orthogonal decomposition (POD) to estimate the effect of control on sweep events within an opposition control framework. Conditionally averaged sweep events (CASEs) were experimentally sampled in a fully turbulent channel flow at a friction Reynolds number of 350. The two architectures were then trained to reconstruct the controlled CASEs using the control parameters (frequency, voltage amplitude, and delay time) as input. The results indicate that both approaches are able to reproduce the control signature across different actuation parameters with comparable accuracy. At the same time, the hybrid POD–FNN architecture requires over two orders of magnitude fewer trainable parameters. Finally, both local and global sensitivity analyses were performed, leveraging the differentiability of the trained models and their rapid inference times. The Jacobian matrix and Sobol indices were computed to conduct a local and a global sensitivity analysis, respectively. The findings revealed a high sensitivity to the actuation frequency and delay time parameters, whereas a lower sensitivity was observed with respect to the voltage amplitude.