Haut PDF LES analysis of jets in cross flow

LES analysis of jets in cross flow

LES analysis of jets in cross flow

A really great number of experimental campaigns 1 have been conducted upon this subject and the outcomes demonstrated that, typically, thermal loads characterized by ∆T of about 160 K and ω between 3 and 10 Hz, seems to create favorable conditions to crack initiations. Beside the aim of providing the critical intervals of this parameters, experimental data have been also produced to val- idate Computational Fluid Dynamics (CFD) codes and further model’s developments. In fact, due to correctly predict and avoid thermal striping problems, CFD tools shows an interesting potential and its application can lead to an in-depth comprehension upon complex operating conditions and geometries which are difficult and/or expensive to be reproduced for empirical investigations. In a large part of cases, turbulent flows can be described with good accuracy and small computational costs by using two-equation models for solving Reynolds Averaged Navier-Stokes Equations (RANS) whenever the user aims to obtain consistent time-averaged fields. On the other hand, for obtaining reasonable values in terms of local time fluctuations, Large Eddy Simulation (LES) shows higher potentials with better capabilities, despite its greater computational costs, on catching the desired parameters for thermal fatigue analysis. However, detailed validations on CFD codes are still needed to achieve a better comprehension on their limits whenever they’re used for studying such kind of phenomenon. In the present paper, two experimental campaigns are taken in account as a measuring tape for evaluate the TrioCFD code developed in the Saclay research center of CEA.
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Distributions of critical flux: modelling, experimental analysis and consequences for cross-flow membrane filtration

Distributions of critical flux: modelling, experimental analysis and consequences for cross-flow membrane filtration

4.4. Application of DCF model to the gel theory Formation of a gel layer could be considered as one of these phase transitions. This analogy has been underlined by a model [13] for the description of gel and deposit formation from the concentration polarisation where critical flux defines both these transitions. The DCF model developed in this paper could then describe the formation of a gel with heterogeneous properties. As a first confirmation of this assumption, the DCF model has been applied to the description of bovine serum albumin (BSA) ultrafiltration [22]. Prior to these ultrafiltration experiments, the membrane was fouled using the BSA solution, in such a way that adsorption during the UF run could be ignored. In the same way as when considering latex filtration, the curve of steady state flux versus TMP can be fully depicted (Fig. 12) by the distribution parameters with, by analogy, a mean critical flux for gel, J crit , and its
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Distributions of critical flux: modelling, experimental analysis and consequences for cross-flow membrane filtration

Distributions of critical flux: modelling, experimental analysis and consequences for cross-flow membrane filtration

However, such a sharp transition is not often observed in practice and discrepancies between the concept and experiments are observed. Even experimental works carried out with well characterized suspensions and membranes often exemplify this discrepancy [5,6] and this is further presented in the experimental section of this paper. To take this into account, the concept of critical flux has sometimes evolved by distinguishing a weak form of critical flux from the original strong form of critical flux [7]. The weak form of critical flux is based on the subtle difference between slow fouling conditions (inducing permeability smaller than that obtained with a clean membrane filtering pure water) and faster fouling (inducing a deviation from the initial linearity of the J vs TMP curve). The weak form of critical flux thus shows its ability to describe experiments with numerous fluids from model fluids to complex ones [7]. However, this weak form of critical flux loses the original significance of the previous concept of critical flux and has no direct theoretical grounding.
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CFD analysis of non-axial flow in fuel assemblies

CFD analysis of non-axial flow in fuel assemblies

F-91191 GIF-sur-Yvette ulrich.bieder@cea.fr ABSTRACT CFD studies with the Trio_U code were performed to evaluate the flow field and pressure drop in rod bundles with a slope angle of 22° between main flow and the axis of the rods. Comparison to the CEA experimental program EOLE is discussed which was performed with inclined rod bundles in in a square channel. Finally, the inter-assembly flow in two adjusted parts of fuel assemblies, separated by the assembly bypass flow, is analyzed. The large eddy simulation (LES) method is used to account for non- isotropic turbulence. A mesh of 1.1 billion control volumes was used for this analysis. The simulation has been performed on 10,000 processor cores of the HPC computer CURIE of the TGCC. The correlation of the EOLE program under estimates the pressure drop of the assembly calculation by a factor of about six. In contrary to the flow in the open, unbounded core region modeled by the assembly calculation, the EOLE experiments have been performed in a square channel. Thus, questions rise concerning the applicability of correlations derived from a channel configuration to the unbounded core region. Simulating the flow in the inclined rod bundle of the EOLE experiment by using the open boundary conditions of the assembly calculation confirms the under prediction of the correlation.
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Parametric optimization of pulsating jets in unsteady flow by Multiple-Gradient Descent Algorithm (MGDA)

Parametric optimization of pulsating jets in unsteady flow by Multiple-Gradient Descent Algorithm (MGDA)

The application of an optimization procedure to such problems is faced to the following difficulties: first, the choice of the optimization algorithm is conditioned by the huge computational time of the unsteady-flow simulation, and second, it is necessary to consider several objectives concurrently. Typically, the improvement of the single time-averaged performance is usually not satisfactory for realistic ap- plications. Secondly, sensitivity analysis is tedious in the context of unsteady flows, due to the backward integration of the adjoint equation, which requires the storage, or partial storage / partial re-computation, of the unsteady solution.
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On the relative impact of subgrid-scale modelling and conjugate heat transfer in LES of hot jets in cross-flow over cold plates

On the relative impact of subgrid-scale modelling and conjugate heat transfer in LES of hot jets in cross-flow over cold plates

KEY WORDS : fluid-structure coupling; conjugate heat transfer; large eddy simulation; hot jet in cross- flow; subgrid-scale modelling; transverse jet 1. INTRODUCTION Aerothermal flows are ubiquitous in industrial applications especially in aeronautics. Some exam- ples are cooling jets along the blades of gas turbines or anti-ice systems on planes, which are both related to the canonical problem of a jet in cross-flow (JCF). To solve this problem numerically, (Unsteady-) Reynolds Averaged Navier–Stokes (RANS) simulations were conducted and it was shown that simple two-equation models such as the standard k   model were able to predict the gross flow field, but did not reproduce well the average lateral jet width and the average jet’s pene- tration in the cross-flow [1, 2]. Turbulent statistics also seem difficult to predict with these methods. Because certain parts of the flow are strongly anisotropic, Reynolds Stress Models were expected to be more accurate but they were not found to do especially better than two-equation models [1]. This may be linked to the need to resolve the temporal behaviour of the jet or to find closures for the pressure–velocity and triple velocity correlations satisfactory for both in a jet regime and in a boundary layer regime. Because computer power is continuously increasing, it is now conceivable to use LESs, which do not suffer from these problems of flexibility, to study some of these complex flows. In comparison to RANS simulations, LES have provided better agreement with experimental data (e.g. [3–5]). During the last two decades, the subgrid-scale (SGS) models used in these LES have considerably evolved since Smagorinsky’s pioneering work [6]. Almost every new model has shown improvements over previous ones when tested in academic simulations. However, it is more
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AC electrified jets in a flow-focusing device: Jet length scaling

AC electrified jets in a flow-focusing device: Jet length scaling

V. CONCLUSIONS Long water jets in a flow focusing device were generated upon application of AC fields. The length of the jet was measured as a function of water conductivity, signal frequency, and voltage amplitude. It was found a threshold voltage above which the jet length increases very fast. The measurements of the length show a hysteresis loop around this threshold voltage. For high frequencies of the AC signal (f 10 kHz), the transition to long jets is not abrupt and the hysteresis disappears. The distributed element circuit model of the system provides a way of evaluating the electric potential at the tip of the jet as a function of the electrical parameters. We found that, for all combinations of these parameters at which a long jet is formed, the elec- tric potential at the tip of the jet is around 550 V. This result, together with the similarity of the tip geometry for all long jets, seems to confirm our hypothesis that the jet breakup occurs for a given electric field distribution around the tip. For low frequencies of the AC signals, we
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Lagrangian and spectral analysis of the forced flow past a circular cylinder using pulsed tangential jets

Lagrangian and spectral analysis of the forced flow past a circular cylinder using pulsed tangential jets

This method, referred to as the dynamic mode decomposition (DMD), has successively been applied to image-based flow visualization of a laminar axisymmetric jet (Schmid 2009 ), lid-driven cylindrical cavity particle image velocimetry (PIV) measurements (Schmid, Meyer & Pust 2009 ), jet in cross-flow direct numerical simulation (DNS) data (Rowley et al. 2009 ) or transitional water jet tomo-PIV measurements (Schmid et al. 2010 ). See also Schmid ( 2010 ) for further applications. In particular, Rowley et al. ( 2009 ) demonstrated that whereas a single proper orthogonal decomposition (POD) mode may be associated with more than one frequency, a DMD mode is exclusively linked to one given frequency. The interest for unsteady flow control applications is hence straightforward since DMD has the capability to isolate a specific time scale, allowing, for instance, the characterization of the flow dynamics associated with the actuator by knowing its actuation frequency.
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Analysis of tip leakage flow noise inception in axial fans

Analysis of tip leakage flow noise inception in axial fans

A more complex series of experiments was carried out at Virginia Tech on a linear cascade in order to investigate the inception of tip gap flow features. Work was carried out on a 8 blade compressor cascade at a Reynolds number around 450 000 based on a 254 mm chord length, corresponding to a Mach number of 0.08. Muthanna [Muthanna, 1998], using hotwire sensors, pressure taps and surface oil visualizations, observed the formation of the aforementioned cross-flow perpendicular to the chord across the tip clearance of the blade cascade. The cross-flow then rolled up into the so-called tip leakage vortex (TLV) when encountering the free-stream at the suction side and peeling away towards the pressure side of the following blade. A secondary vortex structure with opposing but relatively lower vorticity when compared to the tip vortex also formed near the suction side tip edge. Varying the tip clearance also influenced the observed vortices, with a larger gap increasing the TLV strength and zone of influence, and moving its detachment point along the blade chord. On the opposite side of the spectrum, a small enough gap prevents the formation of the TLV, instead leading to the formation of a high shear flow layer along the shroud casing originating from the clearance gap. It was observed, however, that with the TLV present, it becomes the main source of turbulence in the flowfield, dominating even the blade wakes downstream of the blade cascade. Wang [Wang, 2000] investigated the effect of adding a moving shroud wall to simulate the relative movement between the blades and the shroud casing in a functional rotor assembly. It was found that it only served to flatten the TLV in the spanwise direction, but did not interfere with the mechanisms behind the formation of the structures. Their findings were also confirmed by laser Doppler velocimetry measurements [Tang, 2004].
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Scaling and dimensional analysis of acoustic streaming jets

Scaling and dimensional analysis of acoustic streaming jets

(Received 20 November 2013; accepted 25 August 2014; published online 18 September 2014) This paper focuses on acoustic streaming free jets. This is to say that progressive acoustic waves are used to generate a steady flow far from any wall. The derivation of the governing equations under the form of a nonlinear hydrodynamics problem coupled with an acoustic propagation problem is made on the basis of a time scale discrimination approach. This approach is preferred to the usually invoked ampli- tude perturbations expansion since it is consistent with experimental observations of acoustic streaming flows featuring hydrodynamic nonlinearities and turbulence. Experimental results obtained with a plane transducer in water are also presented together with a review of the former experimental investigations using similar con- figurations. A comparison of the shape of the acoustic field with the shape of the velocity field shows that diffraction is a key ingredient in the problem though it is rarely accounted for in the literature. A scaling analysis is made and leads to two scaling laws for the typical velocity level in acoustic streaming free jets; these are both observed in our setup and in former studies by other teams. We also perform a dimensional analysis of this problem: a set of seven dimensionless groups is required to describe a typical acoustic experiment. We find that a full similarity is usually not possible between two acoustic streaming experiments featuring different fluids. We then choose to relax the similarity with respect to sound attenuation and to focus on the case of a scaled water experiment representing an acoustic streaming application in liquid metals, in particular, in liquid silicon and in liquid sodium. We show that small acoustic powers can yield relatively high Reynolds numbers and velocity levels; this could be a virtue for heat and mass transfer applications, but a drawback for ultrasonic velocimetry.  C 2014 AIP Publishing LLC. [ http://dx.doi.org/10.1063/1.4895518 ]
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Design an Experiment for Studying an Elastic Cylinder in Cross-Flow

Design an Experiment for Studying an Elastic Cylinder in Cross-Flow

Figure 1.1: Elastically mounted rigid cylinder in uniform cross-flow (a) single-degree-of-freedom model (b) two-degree-of-freedom model. 1.2 Need for Experimental Study The primary objective of this work is to gather required information to design an experiment to study elastic structures’ response in steady incompressible cross-flow. The motivation for the present work is that we still do not have a full understanding of the vortex-excited oscillations of elastic slender structures. While the response of actual structures is a combination of in-line and cross-flow motion, most of the studies up to now have focused on the cross-flow or in-line oscillations, but not both of them simultaneously. On the other hand the particular case of a cantilever vertical beam has not received enough attention, while it appears in some applications such as smoke stacks and off/onshore meteorological towers. This makes it necessary to perform a thorough analysis to understand the behavior of elastic cylindrical structures undergoing two- degree-of-freedom oscillations in cross-flow.
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Comparison of the Z/γ[superscript ∗] + jets to γ + jets cross sections in pp collisions at √s = 8 TeV

Comparison of the Z/γ[superscript ∗] + jets to γ + jets cross sections in pp collisions at √s = 8 TeV

ph distribution for the data is fitted as a sum of signal and background template distributions, in each pT bin, in order to calculate the purity f : I ph PF (data) = f I ph PF (signal) + (1 − f ) I ph PF (background). In order to model the contribution of the underlying event to the photon component isolation sum around the signal photon candidate, a signal template is obtained from the data through the random-cone (RC) method [ 47 ]. After selecting photon candidates fulfilling a requirement on the shower shape of σηη < 0.011, a cone of ∆R = 0.4 is randomly chosen in φ at the same η as the photon candidate, excluding the back-to-back direction to avoid selecting any recoiling jet. The candidate cone is rejected if it contains objects originating from a hard interaction, e.g., jets with pT > 30 GeV or photons with pT > 20 GeV. The RC templates show a very good agreement over orders of magnitude between data, simulation, and the true-photon MC templates obtained by matching a detector-level photon candidate with an isolated photon at the particle level. Background templates are constructed by selecting photon candidates in the data with an inverted shower shape requirement, 0.011 < σ ηη < 0.014. Since there are a small number of background events with high pT photon candidates, the templates are obtained in wider bins of p γ T than used in the final analysis. After construction of the templates, a binned maximum-likelihood fit to the I PF
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Analysis of membrane fouling during cross-flow microfiltration of wine

Analysis of membrane fouling during cross-flow microfiltration of wine

3.3. Wine analysis For wine component quantification, spectrophotometric analyses were carried out on an Agilent 8453 UV/VIS spectrophotometer. Total polyphenols in wine were estimated by the total polyphenol index (TPI) using the absorption at 280 nm and under 1 cm optical path. Color intensity (IC) is the sum of optical densities at 420 nm, 520 nm and 620 nm under 1 mm optical path. Total polysaccharides were determined using the modified Usseglio-Tomasset method based on the precipitation of the polysaccharides with ethanol ( Usseglio-Tomasset, 1976 ). Total anthocyanins were determined according to the Ribéreau-Gayon method using the sodium bisulphite ( Ribéreau-Gayon et al., 2006 ). Total tannins were also determined according to the Ribéreau-Gayon method by transforming the proanthocyanidins into anthocyanidins ( Ribéreau-Gayon et al., 2006 ). Tannins were also analyzed using the method of thioacidolysis as described by Preys, Souquet, Meudec, Morel-Salmi, and Cheynier (2004) . The measurements were performed with a UHPLC (DIONEX, Ultimate 3000 RSLC) and the used column was a Kinetex® PFP (Phenomenex). pH, alcohol content, malic acid, glucose and fructose concentration were determined on the wine by FTIR spectroscopy (Fourier Transform Infra-Red spectroscopy). Mannoproteins were de- termined using the total polysaccharide method. Wine viscosity is de- termined with a controlled-stress rheometer (AR-2000 ex). Turbidity measurements (NTU) were performed with a Eutech TN-100 turbi- dimeter (Eutech Instruments, Singapore).
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Analysis of membrane fouling during cross-flow microfiltration of wine

Analysis of membrane fouling during cross-flow microfiltration of wine

4.2.1. Pectins impact on cross-flow filtration performances Fig. 8 shows the experimental data of the permeate fluxes as a function of filtered volume during constant ΔP (0.5 and 1 × 10 5 Pa) cross-flow microfiltration for wines containing pectins at different concentrations (0.25 and 0.5 g/l). Transmembrane pressure seems to only affect the initial permeate flux. At the end of the filtrations, no real differences have been noticed in terms of permeate flux for wines containing 0.25 and 0.5 g/l pectins when increasing the trans- membrane pressure. Results showed a severe fouling comparing to filtrations with FW alone. The presence of pectins had a noticeable in- fluence even from the first seconds of filtration independently of pec- tin concentration. This assumption was confirmed by a last trial with the pectin concentration divided by 5 (0.05 g/l) compared to the ini- tial lowest tested concentration (0.25 g/l). At 0.5 bar, mean permeate flux observed for wines containing pectins ranges between 75% (FW + 0.05 g/l pectin) and 85% (FW + 0.5 g/l pectin) lower than the mean permeate flux of the FW.
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Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors

Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors

D l ; (1) where T denotes the stage torque, D the mean wheel diameter and l the blade span. The Alford β parameter was originally conceived as the change in thermodynamic efficiency per unit change in normalized clearance. In practice β has become an em- pirical factor to match computational predictions to experimental data. If β is positive, the net tangential force on the rotor F θ is in the direction of shaft rotation inducing forward whirl. Similarly, a negative β indicates backward whirl tendency. It is recognized that axial flow turbines tend to generate forward rotor whirl. The early analysis for turbines set the foundation for new research and created an important empirical factor that is considered in the design of modern jet engines and gas turbines.
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Oscillations of Continuous Elastic Cylindrical Structures in Cross-Flow

Oscillations of Continuous Elastic Cylindrical Structures in Cross-Flow

The primary objective of the thesis is to study an elastic structures’ response in steady incompressible flow. While the goal is to examine the case of a uniform velocity profile, a linearly varying velocity profile might be considered by the end of the work, as well. The motivation for the present work is that we still do not have a full understanding of the vortex-excited oscillations of elastic slender structures. While the response of actual structures is a combination of in-line and cross-flow motion, most of the studies up to now have focused on the cross-flow or in-line oscillations, but not both of them simultaneously. On the other hand the particular case of a cantilevered vertical beam has not received enough attention, while it appears in some applications such as smoke stacks and off/onshore meteorological towers. In addition to that, most of the studies have considered an elastically mounted rigid cylinder, while in practice elastic cylindrical structures are commonly used. This makes it necessary to perform a thorough analysis to understand the behavior of elastic cylindrical structures undergoing two-degree-of-freedom oscillations in cross-flow.
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Evolution: Why all plumes and jets evolve to round cross sections

Evolution: Why all plumes and jets evolve to round cross sections

question and explain in this paper: the jet cross section evolves from nozzle-shaped to round, not the other way. At bottom, the phenomenon explained in this paper adds to the growing evidence that the tendency toward evolutionary organiza- tion in nature is governed by a physics principle. In particular, the tendency toward round cross sections in simple (one stream) con- figurations unites the animate with the inanimate flow systems. Without exception, the cross sections tend to the round shape: blood vessels, pulmonary airways, subterranean rivers, large pores (‘‘pipes’’) in the hill slope, underground galleries of moles and earth- worms, tunnels, intestines and many other features of animal design. In river channels, this natural tendency is made visible by the pro- portionality between depth and width in rivers of all sizes 4,19 .
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Spectral analysis of unsteady flow simulation in a small VAWT

Spectral analysis of unsteady flow simulation in a small VAWT

wind turbines from Hau (2000) In 2008, F. Penet, P. de Bodinat and J. Valette gained an innovation price for an idea in which this kind of turbine is used to make a publicity panel lighted by wind energy. They created the society Windisplay to design, create and send such a product. The present study concerns this kind of VAWT technology in which each blade combines a rotating movement around its own axis and a rotating movement around turbine’s axis. It is an extensive study of a work given by this young people. This paper concerns the industrial one.
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Numerical and experimental study of mini synthetic jets actuators for flow control

Numerical and experimental study of mini synthetic jets actuators for flow control

The effects of the SJA on the boundary layer of the cross flow are clearly visible on these profiles (figure 8). At the slot level, the velocity magnitude is strongly increased for z < 2 mm. This is mainly due to the vertical component of the synthetic jet velocity at the slot exit. It was not possible indeed to identify z and x components of the velocity with a single hot wire probe. Nevertheless, it can be seen that the synthetic jet is bended by the cross flow : the z position of the interaction zone is increasing, moving downstream from the SJA position up to x = 100 mm. On the following profiles, the flow velocity is reduced, mainly in the boundary layer, when the SJA is switched on. This is due to the presence of a recirculation zone created by the "right" vortices generated by the SJA and convected downstream by the cross flow. This phenomena apparition is dependent on the ratio between the synthetic jet maximum velocity at the slot exit plane and the cross flow free stream velocity. In their numerical study, Mittal (Mittal et al., 2001) have observed
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Measurement of Top Pair Production Cross-Section in l + jets Channels in ATLAS at 7 TeV

Measurement of Top Pair Production Cross-Section in l + jets Channels in ATLAS at 7 TeV

energy deposit width w η2 in the second sampling are efficient to reject jets of high energy and wide showers. Photon conversions are further reduced by requiring a good quality track pointing to an electromagnetic cluster with good energy-momentum match. After the electron candidates are selected, an “isem” flag is used to define whether any of the electron identification cuts has passed or not. Basically there are three levels “loose”, “medium” and “tight” of “isem”, where “medium” is used on the first stage of our analysis. Once in the future, the variables which are used to define the “isem” flag are better understood, “tight” electrons are more favorable. Figure 3.8 displays the transverse energy and pseudo rapidity spectra for the “medium” electron candidates with comparison between 7 TeV data and Monte Carlo. Generally, shower shape variables of the second calorimeter layer and hadronic leakage variables are used in the “loose” electron selection. First calorimeter layer cuts, track quality requirements and track-cluster matching are added at the level of the “medium” electron selection. The “tight” electron selection adds E/p ratio, b-layer hit requirements and the particle identification potential of the TRT. All those variables used in the “loose”, “medium” and “tight” selections are listed in Table 3.4
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