Liquid jet and droplet deformation induced by non-uniform acoustics radiation pressure distribution

International audienceThe present work focuses on non linear acoustic effects on an elliptic cylinder or an ellipsoid. These effects are encountered in acoustic levitation, ultrasonic standing wave atomization or two-phase flow combustion instabili-ties. Theoretical approaches mainly paid attention on the total radiation force, but a modeling of the distribution of acoustic radiation pressure around the object is needed to predict liquid object deformation. In the present study, a semi-analytical model is presented in order to compute the local radiation pressure as the only reason for liquid jet or droplet deformation. The method used here imposes an incident field to, a posteriori, compute the scattered field as a function of the object geometrical properties. A partial wave decomposition(PWD) model is developed to express incident and scattered fields by and immovable object with rigid boundary conditions. Radiation pressure is computed for progressive and standing wave fields. Validation of our method is done by comparing with the radiation force results from the literature. Results show that the larger the deformation, the higher the acoustic effects in a direction perpendicular to the acoustic wave axis. Introduction Non linear effects of acoustics are encountered in applications such as acoustic levitation, ultrasonic standing wave atomization or two-phase flow combustion instabilities occurring in rocket engines [1-4]. Most of the studies dealing with interaction of acoustics and spherical [5-9] or cylindrical [10-14] objects focused on the stationary radiation force. The main objective was there to determine the displacement of these objects. However, their deformation is also of a great interest in applications dealing with liquid objects. In studies on acoustically levitating droplets, some authors considered the radiation pressure distribution as the source of the stationnary deformation of the free surfaces [2, 15, 16]. They showed that spherical droplets became oblate when exposed to the radiation pressure. For cylindrical objects, it was experimentally proven that cylindrical liquid jets subjected to a low frequency standing wave were susceptible to be deformed into elliptic cylinders [17]. Thus, by relying on those results it appeared that knowing radiation pressure distribution around elliptic objects was necessary to correctly analyze the interaction between acoustics and deformed objects. Hasheminejad et al. [18, 19] developed an approach based on elliptic functions, namely Mathieu functions, to describe the acoustic scattered field. This is a powerful method, but limited in its applications due to the occurrence of Mathieu polynomials instability. Other authors considered a theoretical approach based on the expression of the incident and scattered waves by means of the formal cylindrical or spherical functions [17, 20-22]. All the studies cited above focused only on the modeling of the radiation force computed with the far field assumption avoiding the computation of radiation pressure distribution. To tackle the problem of object deformation induced by acoustics, it is needed to model the radiation pressure distribution. This is done here for elliptic cylinders and ellipsoids. The two-way coupling between incident acoustic harmonic plane waves and these objects is explored by computing the radiation pressure field and resulting radiation force. In the first section is presented the method used to compute the acoustic velocity potential field scattered by elliptic objects and the consequent computation of the radiation pressure and radiation force. Results showing the convergence of the method, its validation and the radiation pressure distribution are presented in the second section. Finally, the last section is dedicated to some conclusions

Acoustic response of a feeding system to high-frequency transverse acoustic field

International audienceThe acoustic coupling between the injection system and the acoustic fluctuations in liquid rocket engine combustion chambers is an important issue in the understanding of the thermo-acoustic instability phenomenon. This paper presents results of a large parametric investigation of a two-phase injection system acoustic response, to the excitation produced by a high-amplitude transverse acoustic field forced into a main resonant cavity. Two domes, one for the gas and one for the liquid, were expressly designed to feed three identical coaxial injectors. Characterization of domes internal mode shapes were performed by measuring pressure signals at different locations in the domes. Experimental mode shapes showed good agreement with those predicted by numerical simulations. Acoustic pressure amplitudes up to 17% of the the one induced in the main cavity can be found in both gas and liquid dome. The maximum acoustic response is observed in a configuration in which acoustic boundary conditions does not correspond to the maximum injection system solicitation conditions

Acoustic response of a feeding system to high-frequency transverse acoustic field

International audienceThe acoustic coupling between the injection system and the acoustic fluctuations in liquid rocket engine combustion chambers is an important issue in the understanding of the thermo-acoustic instability phenomenon. This paper presents results of a large parametric investigation of a two-phase injection system acoustic response, to the excitation produced by a high-amplitude transverse acoustic field forced into a main resonant cavity. Two domes, one for the gas and one for the liquid, were expressly designed to feed three identical coaxial injectors. Characterization of domes internal mode shapes were performed by measuring pressure signals at different locations in the domes. Experimental mode shapes showed good agreement with those predicted by numerical simulations. Acoustic pressure amplitudes up to 17% of the the one induced in the main cavity can be found in both gas and liquid dome. The maximum acoustic response is observed in a configuration in which acoustic boundary conditions does not correspond to the maximum injection system solicitation conditions

High amplitude/high frequency acoustic field effects on coaxial inkection

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Response of coaxial air-assisted liquid jets in an acoustic field: atomization and droplets clustering

International audienceHigh-frequency combustion instabilities have been proven to be extremely harmful to liquid rocket engine operation , even leading to the destruction of the combustion chamber. The coupling between acoustic field and combustion heat release rate in the combustion chamber is considered as the driving phenomenon. Experiments have shown that intense acoustic field can deeply affect atomization process thereby causing a non-uniform heat release distribution which can couple with the resonant mode shapes of the combustion chamber and consequently trigger or sustain combustion instability. The effects of acoustic acting on atomization of coaxial air-assisted liquid jets have been investigated experimentally and results are presented in this paper. The experimental setup is composed of three coaxial injectors installed on the roof of a semi-open resonant cavity provided with 4 compression drivers. An acoustic field corresponding to the 2 nd transverse mode of the cavity is forced into that at a frequency of 1 kHz. Acoustic levels up to 174 dB are produced. High speed visualizations are performed in order to observe the response of the jet to the acoustic perturbations. In the case of low Weber numbers (We < 30) the jet can be considered as cylindrical and depending on the position of the injector with respect to the acoustic axis different responses can be observed. If the injector is placed in correspondence of the velocity antinode the jet is flattened into a liquid sheet perpendicular to the acoustic axis, if the injector is located in correspondence of an intensity antinode the jet is deviated toward the velocity antinode. Combined response can be observed at intermediate positions. For higher Weber numbers the jet is no more cylindrical and a spray is formed, characterized by with a certain spray angle. Such a spray is can still be affected by the acoustics but it is not always possible to get evidence of this from observation of raw images. To quantify these effects, image analyses have been carried-out to determine how spatial distributions of droplets are affected by acoustics. Results are presented for Weber numbers ranging from 30 to 1500, with and without acoustic. Clustering of droplets is shown as well as improvement of atomization process

Acoustic response of an injection system to high-frequency transverse acoustic fields

International audienceThe acoustic coupling between the injection system and the acoustic fluctuations in liquid rocket engine combustion chambers is an important issue in the understanding of the thermo-acoustic instability phenomenon. This paper presents the results of a wide-ranging parametric investigation of the acoustic response of a two-phase injection system submitted to a forced high-amplitude transverse acoustic field. Two domes, one for the gas and one for the liquid, were expressly designed to feed three identical coaxial injectors. The internal mode shapes of the domes were characterized by measuring pressure signals at different locations in the domes. Experimental mode shapes showed good agreement with those predicted by numerical simulations. Acoustic pressure amplitudes up to 23% of those induced in the main cavity can be found in both the gas and liquid domes. The response efficiency in a dome depends on the position of the injectors' exit in the acoustic field

Mitochondrial Dysregulation in the Pathogenesis of Diabetes: Potential for Mitochondrial Biogenesis-Mediated Interventions

Muscle mitochondrial metabolism is a tightly controlled process that involves the coordination of signaling pathways and factors from both the nuclear and mitochondrial genomes. Perhaps the most important pathway regulating metabolism in muscle is mitochondrial biogenesis. In response to physiological stimuli such as exercise, retrograde signaling pathways are activated that allow crosstalk between the nucleus and mitochondria, upregulating hundreds of genes and leading to higher mitochondrial content and increased oxidation of substrates. With type 2 diabetes, these processes can become dysregulated and the ability of the cell to respond to nutrient and energy fluctuations is diminished. This, coupled with reduced mitochondrial content and altered mitochondrial morphology, has been directly linked to the pathogenesis of this disease. In this paper, we will discuss our current understanding of mitochondrial dysregulation in skeletal muscle as it relates to type 2 diabetes, placing particular emphasis on the pathways of mitochondrial biogenesis and mitochondrial dynamics, and the therapeutic value of exercise and other interventions

Sternal reentry in a patient with previous deep sternal wound infection managed with horizontal titanium plate fixation

Redo open-heart surgery and sternal reentry in patients with previous deep sternal wound infection (DSWI) and absence of sternal integrity can be a delicate and morbid task due the lack of a dissection plane between the heart and the surrounding soft tissues. Delayed sternal reconstruction and osteosynthesis with horizontal titanium plating fixation (Synthes) following vacuum assisted therapy (KCI) has recently been proposed and adopted for the treatment of DSWI. We present such a case of a patient who was successfully reoperated for valve replacement three years after coronary artery bypass grafting complicated by DSWI and initially treated with titanium plate fixation

Metabolic syndrome increases operative mortality in patients undergoing coronary artery bypass grafting surgery

OBJECTIVES: The aim of this study was to determine the impact of the metabolic syndrome (MS) on operative mortality after a coronary artery bypass grafting surgery (CABG). BACKGROUND: Diabetes and obesity are highly prevalent among patients undergoing CABG. However, it remains unclear whether these factors have a significant impact on operative mortality after this procedure. We hypothesized that the metabolic abnormalities associated with MS could negatively influence the operative outcome of CABG surgery. METHODS: We retrospectively analyzed the data of 5,304 consecutive patients who underwent an isolated CABG procedure between 2000 and 2004. Of these 5,304 patients, 2,411 (46%) patients met the National Cholesterol Education Program-Adult Treatment Panel III criteria for MS. The primary end point was operative mortality. RESULTS: The operative mortality after CABG surgery was 2.4% in patients with MS and 0.9% in patients without MS (p < 0.0001). The MS was a strong independent predictor of operative mortality (relative risk 3.04 [95% confidence interval (CI) 1.73 to 5.32], p = 0.0001). After adjusting for other risk factors, the risk of mortality was increased 2.69-fold (95% CI 1.43 to 5.06; p = 0.002) in patients with MS and diabetes and 2.36-fold (95% CI 1.26 to 4.41; p = 0.007) in patients with MS and no diabetes, whereas it was not significantly increased in the patients with diabetes and no MS. CONCLUSIONS: This is the first study to report that MS is a highly prevalent and powerful risk factor for operative mortality in patients undergoing a CABG surgery. Thus, interventions that could contribute to reduce the prevalence of MS in patients with coronary artery disease or that could acutely modify the metabolic perturbations of MS at the time of CABG might substantially improve survival in these patient

Zénon (de Citium ou) d’Athènes

Dictionnaire des philosophes antiques, vol. VI