Cavitation Bubble Cloud Break-Off Mechanisms at Micro-Channels

This paper provides new physical insight into the coupling between flow dynamics and cavitation bubble cloud behaviour at conditions relevant to both cavitation inception and the more complex phenomenon of flow “choking” using a multiphase compressible framework. Understanding the cavitation bubble cloud process and the parameters that determine its break-off frequency is important for control of phenomena such as structure vibration and erosion. Initially, the role of the pressure waves in the flow development is investigated. We highlight the differences between “physical” and “artificial” numerical waves by comparing cases with different boundary and differencing schemes. We analyse in detail the prediction of the coupling of flow and cavitation dynamics in a micro-channel 20 m high containing Diesel at pressure differences 7 MPa and 8.5 MPa, corresponding to cavitation inception and "choking" conditions respectively. The results have a very good agreement with experimental data and demonstrate that pressure wave dynamics, rather than the “re-entrant jet dynamics” suggested by previous studies, determine the characteristics of the bubble cloud dynamics under “choking” conditions.

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Scaling of Cavitation Bubble Cloud Dynamics on Propellers

Advanced Experimental and Numerical Techniques for Cavitation Erosion Prediction - Fluid Mechanics and Its Applications ◽

10.1007/978-94-017-8539-6_15 ◽

2014 ◽

pp. 345-372 ◽

Cited By ~ 8

Author(s):

Georges L. Chahine ◽

Chao-Tsung Hsiao ◽

Reni Raju

Keyword(s):

Cavitation Bubble ◽

Bubble Cloud ◽

Cloud Dynamics

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Theoretical Insight into the Reversal of Chemoselectivity in Diels-Alder Reactions of α,β-Unsaturated Aldehydes and Ketones Catalyzed by Brønsted and Lewis Acids

Organics ◽

10.3390/org2010004 ◽

2021 ◽

Vol 2 (1) ◽

pp. 38-49

Author(s):

Lakhdar Benhamed ◽

Sidi Mohamed Mekelleche ◽

Wafaa Benchouk

Keyword(s):

Lewis Acids ◽

Major Product ◽

Diels Alder ◽

Unsaturated Ketone ◽

Unsaturated Aldehydes ◽

Aldehydes And Ketones ◽

Theoretical Insight ◽

Insight Into ◽

Good Agreement

Experimentally, a reversal of chemoselectivity has been observed in catalyzed Diels–Alder reactions of α,β-unsaturated aldehydes (e.g., (2E)-but-2-enal) and ketones (e.g., 2-hexen-4-one) with cyclopentadiene. Indeed, using the triflimidic Brønsted acid Tf2NH as catalyst, the reaction gave a Diels–Alder adduct derived from α,β-unsaturated ketone as a major product. On the other hand, the use of tris(pentafluorophenyl)borane B(C6F5)3 bulky Lewis acid as catalyst gave mainly the cycloadduct of α,β-unsaturated aldehyde as a major product. Our aim in the present work is to put in evidence the role of the catalyst in the reversal of the chemoselectivity of the catalyzed Diels–Alder reactions of (2E)-but-2-enal and 2-Hexen-4-one with cyclopentadiene. The calculations were performed at the ωB97XD/6-311G(d,p) level of theory and the solvent effects of dichloromethane were taken into account using the PCM solvation model. The obtained results are in good agreement with experimental outcomes.

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Seasonal predictability of Mediterranean weather regimes in the Copernicus C3S systems

Climate Dynamics ◽

10.1007/s00382-021-05681-4 ◽

2021 ◽

Author(s):

Ignazio Giuntoli ◽

Federico Fabiano ◽

Susanna Corti

Keyword(s):

Mediterranean Region ◽

Climate Models ◽

Reanalysis Data ◽

Seasonal Predictability ◽

Economic Implications ◽

Weather Regimes ◽

Weather Patterns ◽

The Mediterranean ◽

Good Agreement

AbstractSeasonal predictions in the Mediterranean region have relevant socio-economic implications, especially in the context of a changing climate. To date, sources of predictability have not been sufficiently investigated at the seasonal scale in this region. To fill this gap, we explore sources of predictability using a weather regimes (WRs) framework. The role of WRs in influencing regional weather patterns in the climate state has generated interest in assessing the ability of climate models to reproduce them. We identify four Mediterranean WRs for the winter (DJF) season and explore their sources of predictability looking at teleconnections with sea surface temperature (SST). In particular, we assess how SST anomalies affect the WRs frequencies during winter focussing on the two WRs that are associated with the teleconnections in which the signal is more intense: the Meridional and the Anticyclonic regimes. These sources of predictability are sought in five state-of-the-art seasonal forecasting systems included in the Copernicus Climate Change Services (C3S) suite finding a weaker signal but an overall good agreement with reanalysis data. Finally, we assess the ability of the C3S models in reproducing the reanalysis data WRs frequencies finding that their moderate skill increases during ENSO intense years, indicating that this teleconnection is well reproduced by the models and yields improved predictability in the Mediterranean region.

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The Role of Equatorial Rossby Waves in Tropical Cyclogenesis. Part I: Idealized Numerical Simulations in an Initially Quiescent Background Environment

Monthly Weather Review ◽

10.1175/2009mwr3114.1 ◽

2010 ◽

Vol 138 (4) ◽

pp. 1368-1382 ◽

Cited By ~ 15

Author(s):

Jeffrey S. Gall ◽

William M. Frank ◽

Matthew C. Wheeler

Keyword(s):

Tropical Cyclone ◽

Large Scale ◽

Phase Speed ◽

Tropical Cyclogenesis ◽

Initial Amplitude ◽

Low Level ◽

Wave Simulation ◽

Horizontal Momentum ◽

Good Agreement

Abstract This two-part series of papers examines the role of equatorial Rossby (ER) waves in tropical cyclone (TC) genesis. To do this, a unique initialization procedure is utilized to insert n = 1 ER waves into a numerical model that is able to faithfully produce TCs. In this first paper, experiments are carried out under the idealized condition of an initially quiescent background environment. Experiments are performed with varying initial wave amplitudes and with and without diabatic effects. This is done to both investigate how the properties of the simulated ER waves compare to the properties of observed ER waves and explore the role of the initial perturbation strength of the ER wave on genesis. In the dry, frictionless ER wave simulation the phase speed is slightly slower than the phase speed predicted from linear theory. Large-scale ascent develops in the region of low-level poleward flow, which is in good agreement with the theoretical structure of an n = 1 ER wave. The structures and phase speeds of the simulated full-physics ER waves are in good agreement with recent observational studies of ER waves that utilize wavenumber–frequency filtering techniques. Convection occurs primarily in the eastern half of the cyclonic gyre, as do the most favorable conditions for TC genesis. This region features sufficient midlevel moisture, anomalously strong low-level cyclonic vorticity, enhanced convection, and minimal vertical shear. Tropical cyclogenesis occurs only in the largest initial-amplitude ER wave simulation. The formation of the initial tropical disturbance that ultimately develops into a tropical cyclone is shown to be sensitive to the nonlinear horizontal momentum advection terms. When the largest initial-amplitude simulation is rerun with the nonlinear horizontal momentum advection terms turned off, tropical cyclogenesis does not occur, but the convectively coupled ER wave retains the properties of the ER wave observed in the smaller initial-amplitude simulations. It is shown that this isolated wave-only genesis process only occurs for strong ER waves in which the nonlinear advection is large. Part II will look at the more realistic case of ER wave–related genesis in which a sufficiently intense ER wave interacts with favorable large-scale flow features.

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C-V and DLTS Investigations of GaAs/InGaAs/GaAs Strained Quantum Well Structures

MRS Proceedings ◽

10.1557/proc-300-115 ◽

1993 ◽

Vol 300 ◽

Author(s):

S. Subramanian ◽

B. M. Arora ◽

A. K. Srivastava ◽

S. Banerjee ◽

G. Fernandes

Keyword(s):

Quantum Well ◽

Band Offset ◽

Full Width ◽

Single Quantum ◽

Single Quantum Well ◽

Quantum Well Structures ◽

Strained Quantum Well ◽

Good Agreement

ABSTRACTIn this paper we report a modified Kroemer's analysis for the determination of the band offset (ΔEc) of single quantum well (SQW) structures from simple C-V measurements. The experimental carrier profile from an MOVPE grown pseudomorphic GaAs/InGaAs/GaAs strained SQW structure shows a sharp accumulation peak bounded by depletion regions on either side. The full width at half maximum of the accumulation peak is comparable to the width of the quantum well. The value of ΔEC obtained from C-V measurement is in good agreement with the values determined by simulation and photoluminescence measurements. DLTS measurements on our SQW samples do not show any peaks which is contrary to the published reports. We believe that it is necessary to carefully isolate the role of interface states, before assigning a DLTS peak to emission from the quantum well.

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Prediction of Cavitation Inception Within Regions of Flow Separation

Journal of Fluids Engineering ◽

10.1115/1.4037505 ◽

2017 ◽

Vol 140 (1) ◽

Cited By ~ 3

Author(s):

Eduard Amromin

Keyword(s):

Experimental Data ◽

Turbulent Flow ◽

Flow Separation ◽

Computational Method ◽

Average Flow ◽

Cavitation Inception ◽

The Core ◽

Good Agreement

Cavitation within regions of flow separation appears in drifting vortices. A two-part computational method is employed for prediction of cavitation inception number there. The first part is an analysis of the average flow in separation regions without consideration of an impact of vortices. The second part is an analysis of equilibrium of the bubble within the core of a vortex located in the turbulent flow of known average characteristics. Computed cavitation inception numbers for axisymmetric flows are in the good agreement with the known experimental data.

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Cavitation Inception Behind a Jet-Propelled Body

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2007-37026 ◽

2007 ◽

Cited By ~ 1

Author(s):

William Hambleton ◽

Eduard Amromin ◽

Roger E. A. Arndt ◽

Svetlana Kovinskaya

Keyword(s):

Velocity Ratio ◽

The Body ◽

Force Balance ◽

Water Tunnel ◽

Minimum Diameter ◽

Cavitation Inception ◽

Initial Comparison ◽

Jet Velocity ◽

Good Agreement

Cavitation inception behind an axissymmetric body driven by a waterjet has been studied experimentally and numerically. Water tunnel tests have been performed with the body mounted on a force balance. The transom of the body contained a nozzle located along the centerline. Tests were carried out for various water tunnel speeds such that jet velocity ratio, VJ/U, could be varied in the range 0 to 2. Distinctly different cavitation patterns were observed at zero jet velocity (when cavitation appeared in spiral vortices in such flows) and at a various jet velocity ratios (when cavitation appeared between counter-rotating vortices around the jet in such flows). Cavitation inception/disappearance has been determined visually. The body drag was also measured. An analytical method for determination of cavitation inception index has been developed on the basis of a viscous-inviscid interaction concept, with employment of special semiempirical approximations for vortices and consideration of surface tension. These approximations have been preliminarily validated for nozzle jet cavitation (for nozzle discharge in co-flow). It was assumed that visualization allows detection of cavities (bubbles) of 0.4mm-0.5mm diameter or larger. The cavitation inception index is defined as the cavitation index for cavities of such minimum diameter when these cavities are located between counter-rotating vortices. The initial comparison of predicted and measured values of the cavitation inception index shows good agreement.

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