21 research outputs found
Overset grid techniques for the simulation of supersonic jet noise
In the present research project the method
of overset grid techniques is used to simulate a compressible supersonic jet and its
emanated aeroacoustic noise field. The computational domain includes the geometry of the
jet nozzle, simulated on curvilinear grids, which are embedded in a cartesian grid. On
all grids the Navier-Stokes equations are solved based on high order compact finite
difference schemes. We will present simulation results for anoverexpanded jet at
low Reynolds numbers
Bumblebees minimize control challenges by combining active and passive modes in unsteady winds
The natural wind environment that volant insects encounter is unsteady and
highly complex, posing significant flight control and stability challenges.
Unsteady airflows can range from structured chains of discrete vortices shed in
the wake of an object to fully developed chaotic turbulence. It is critical to
understand the flight control strategies insects employ to safely navigate in
natural environments. We combined experiments on free flying bumblebees with
high fidelity numerical simulations and lower order modeling to identify the
salient mechanics that mediate insect flight in unsteady winds. We trained
bumblebees to fly upwind towards an artificial flower in a wind tunnel under
steady wind and in a von Karman street (23Hz) formed in the wake of a cylinder.
The bees displayed significantly higher movement in the unsteady vortex street
compared to steady winds. Correlation analysis revealed that at lower
frequencies, less than 10 Hz, in both steady and unsteady winds the bees
mediated lateral movement with body roll, typical casting motion. At higher
frequencies in unsteady winds there was a negative correlation between body
roll and lateral accelerations. Numerical simulations of a bumblebee in similar
conditions permitted the separation of the passive and active components of the
flight trajectories. Comparison between the free-flying and numerical bees
revealed a novel mechanism that enables bees to passively ride out high
frequency perturbations while performing active maneuvers and corrections at
lower frequencies. The capacity of maintaining stability by combining passive
and active modes at different timescales provides a viable means for volant
animals and machines to tackle the control challenges posed by complex
airflows
Multiparametric approach to unravel the mechanism of Strombolian activity at a multivent system: Mt. Etna case study
On 5th July 2014 an eruptive fissure (hereafter referred to as EF) opened at the base of North-East Crater (NEC) of Mt. Etna. EF produced both Strombolian explosions and lava effusion. Thanks to the multiparametric experiment planned in the framework of MEDSUV project, we had the chance to acquire geophysical and volcanological data, in order to investigate the ongoing volcanic activity at EF. Temporary instruments (2 broadband seismometers, 2 microphones, 3-microphone arrays, a high-speed video camera and a thermal-camera) were deployed near the active vents during 15-16 July 2014 and were integrated with the data recorded by the permanent networks.
Several kinds of studies are currently in progress, such as: frequency analysis by Fourier Transform and Short
Time Fourier Transform to evaluate the spectral content of both seismic and acoustic signals; partitioning of
seismic and acoustic energies, whose time variations could reflect changes in the volcanic dynamics; investigation on the intertimes between explosions to investigate their recurrence behaviour; classification of the waveforms, of infrasound events. Furthermore, joint analysis of video signals and seismic-acoustic wavefields outlined relationships between pyroclasts ejection velocity, total erupted mass, peak explosion pressure, and air-ground motion coupling.
This multiparametric approach allowed distinguishing and characterizing individually the behavior of the two
vents active along the eruptive fissure via their thermal, visible and infrasonic signatures and shed light in the
eruptive dynamics.UnpublishedVienna (Austria)5V. Processi eruttivi e post-eruttiv
Computing Supersonic Jet Noise
Understanding and finally minimizing
supersonic jet noise is a fundamental task in the design of supersonic jet engine. The
computation of supersonic jet noise is a formidable challenge ad the last years saw
substantial progress in that direction. In the talk methods for the computation will be
presented. But the successful computation is only a small step towards understanding and
reducing jet noise. In our group, we work on optimization techniques based on adjoint
methods for the reduction if jet noise. Methods and results of forward and backwards
computations of the full compressible Navier-Stokes equations will be presented in the
talk
DNS study of dust particle resuspension in a fusion reactor induced by a transonic jet into vacuum
This paper reports on a two-phase flow Direct Numerical Simulation (DNS) aimed at analyzing the resuspension of solid particles from a surface hit by a transonic jet inside a low pressure container. Conditions similar to those occurring in a fusion reactor vacuum vessel during a Loss of Vacuum Accident (LOVA) have been considered. Indeed, a deep understanding of the resuspension phenomenon is essential to make those reactors safe and suitable for a large-scale sustainable energy production. The jet Reynolds and Mach numbers are respectively set to 3300 and 1. The Thornton and Ning impact/adhesion model is adopted and improved. An advanced resuspension model, which takes into account the dynamics (rolling and slipping) of particles at the wall, is implemented. The use of this model combined with a DNS represents a great novelty in simulating the particle resuspension process. The particles initially deposited at the wall have constant density, whereas their diameters are drawn according to a log-normal distribution, with parameters obtained from experimental data. It has been found that the flow induced motion of wall deposited particles is highly linked with the instantaneous fluid structures and the resuspension phenomenon predominantly affects particles with the largest diameters. Moreover, the jet-deposit interaction is mostly confined within a circumference around the jet of radius approximately equal to the jet diameter