Software development for ionic-electronic conductor modeling based on Matlab

From different circuit models of mixed materials containing ions and electrons, the aim is to solve mathematically their impedance, and to adjust automatically to real measurements in order to obtain the parameters that describe the behavior of these materials.A partir de diferentes modelos circuitales de materiales mixtos que conducen iones y electrones, se pretende resolver matemáticamente su impedancia, ajustando automáticamente a medidas reales para obtener los parámetros que describen el comportamiento de estos materiales.A partir de diferents models circuitals de materials mixtes que condueixen ions i electrons, es pretén resoldre matemàticament la seva impedància, i ajustar automàticament a mesures reals per tal d'obtenir els paràmetres que descriuen el comportament d'aquests materials

Experimental investigation of the transient bleed valve noise

This study presents the first step of an experimental study of the transient bleed valve noise. It was carried out on a simplified TBV geometry composed of a cylindrical inlet pipe leading to a diaphragm or a perforated disk for the purpose of generating pressure drops. Numerous diaphragms and grids have been tested in order to identify parameters that influence the acoustic radiation of the TBV and for NPR (Nozzle pressure ratio) from 1.2 to 3.6 to cover both subsonic and supersonic regimes. A large number of acoustic behaviors have been identified. For diaphragms far field acoustic spectra are dominated by mixing noise for all NPR and by shock-associated noise (screech and broadband shock associated noise (BBSAN)) when the critical value of the NPR delimiting the subsonic and supersonic behavior (NPRc = 1.89)is exceeded. For grids the mixing noise is still present but is composed of two humps. The parametric study allowed to associate the first hump to the noise of an equivalent jet having the smallest diameter encircling the grid perforations while the second is associated to the noise of the outer isolated jets. A first prediction model has thus been proposed based on this double source. Furthermore, the grids other a significant noise reduction in the audible range with respect to a diaphragm of the same cross-section by shifting the radiation towards the high frequencies. The noise associated with supersonic phenomena (screech and BBSAN) are also strongly reduced and even suppressed in most of the tested cases

Experimental investigation of the acoustic role of the output duct in the discharge of a high pressure flow through diaphragms and perforated plates

This work presents the second step of an experimental study of the noise radiated by a complete flow discharge/control system allowing to expand or evacuate a flow under pressure by passing though diaphragms or perforated plates. The first step of the study, focused on the study of the noise radiated by the passage of the flow through the perforated plates/diaphragms, allowed to identify the presence of three distinct radiation sources: a broadband noise associated with the mixing of the flow at the exit of the perforations and which is strongly linked to the geometry, a shock noise (screech and broadband shock associated noise) associated with the presence of shock cells in the ow for supersonic regimes and a tonal noise associated with a feedback loop and appearing for low subsonic operating points. By adding a duct downstream to the discharge zone to be closer to real geometries found in industry, the broadband noise is strongly modified by the appearance of strong acoustic resonances in the outlet duct. These resonances are moreover strongly affected by the operating point which drives the flow intensity in the duct. A simple analytical model is proposed in order to quickly predict the different acoustic modificationscations induced by the outlet duct in case of simple geometries. Finally, the shock noise, as observed without duct, is totally suppressed but is replaced by "base-pressure oscillation" responsible for strong low frequency tones for diaphragms and perforated plates with large cross-sections

Experimental study of the noise radiated by an air flow discharge through diaphragms and perforated plates

An experimental analysis of the noise radiated by a high pressure flow discharge through diaphragms and perforated plates is carried out for a large range of subsonic and supersonic operating conditions (nozzle pressure ratio (NPR) from 1 to 3.6). A parametric study of the geometrical parameters is also achieved to characterize their influence onto the acoustic radiation and ways to reduce it. This reaches from single diaphragms to multi-perforated plates with variable hole diameters and arrangements that are placed at the exit of a duct. Different acoustic behaviors are observed: in all cases the far-field acoustic radiation is dominated by a broadband contribution associated with the turbulent mixing in shear layers. In the diaphragm cases, this broadband noise has similar characteristics as the mixing noise of classical unheated jets while in the multi-perforated plates cases, it is composed of two distinct humps associated with different parts of the jets development. For supersonic regimes, in addition to this broadband radiation, shock associated noise (screech and broadband shock associated noise) appears for all diaphragm cases and for the perforated plate with the closest holes. Finally for the smallest NPR, a high frequency tonal noise has been observed in most of the multi-perforated cases and for the smallest diaphragm. Different regimes of this radiation have also been observed with a possible amplitude modulation of the dominant tone. This radiation may be attributed to vortex shedding due to the sharp section reduction that would trigger a flow resonance between the small ducts of the holes and their sharp edges

Experimental investigation of the noise radiated by a ducted air flow discharge though diaphragms and perforated plates

An experimental investigation of the noise radiated by a ducted high pressure flow discharge through diaphragms and perforated plates is carried out for a large range of subsonic and supersonic operating conditions (Nozzle Pressure Ratio (NPR) from 1.2 to 3.6). A parametric study of the geometrical parameters is also conducted to characterize their influence on the acoustic radiation. This covers configurations from single diaphragms to multi-perforated plates with variable hole diameters and arrangements that are placed inside a cylindrical duct. Compared with the free discharge analysed in a first part of the study (perforated plates placed directly at the output of the duct), the discharge into a duct, which is closer to the practical applications, generates strong acoustic modifications. As expected, the broadband noise is disturbed by strong modulations due to acoustic resonances in the output duct (longitudinal resonances and transversal duct modes). However, as in the free configuration, a strong effect of the plate geometries on the mixing noise is observed, allowing to adapt or reduce this source. In particular, the increase of the ratio between the perforation spacing and the perforation diameter allows reducing the maximum amplitude of the mixing noise. Compared to the free-field discharge, the Sound Pressure Level (SPL) in the ducted configuration is on average proportional to the 6-th power of the velocity instead of the 8-th power. Moreover, there are two dominant frequency humps in the sound spectra. The low frequency one is characterized by a constant Helmholtz number, suggesting that the sound is shaped by the duct geometry, whereas the high frequency one is characterized by a constant Strouhal number suggesting that the sound is directly generated by the flow. Finally, for supersonic operating points, the screech radiation appearing with diaphragms in the free configuration is suppressed when the output duct is added but new high amplitude and low frequency tones appear for the largest diaphragms and perforated plates. These lines are due to a coupling between normal shock oscillations and longitudinal resonances