Effect of nozzle thickness on the self-excited impinging planar jet
TL;DR: In this article, the authors investigated the effect of varying the jet thickness on the pattern of jet oscillation and the frequency of resulting acoustic tone, and found that the jet oscillations are controlled by a fluid-dynamic mechanism for small impingement distances, where the hydrodynamic flow instability controlled the jets oscillation without any coupling with local acoustic resonances.
About: This article is published in Journal of Fluids and Structures.The article was published on 2014-01-01. It has received 18 citations till now. The article focuses on the topics: Jet (fluid) & Jet noise.
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TL;DR: Gosset et al. as discussed by the authors investigated the interaction between the impinging gas jet and the coating liquid film and showed that this self-sustained mechanism is potentially responsible for the non-uniformity of the final coating.
16 citations
TL;DR: In this article, a combination of multiscale Proper Orthogonal Decomposition (mPOD) and correlation analysis is used to identify the dominant traveling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet.
Abstract: We analyze the flow of a planar gas jet impinging on a thin film dragged by a vertical moving wall. In the coating industry, this configuration is known as jet wiping, a process in which impinging jets control the thickness of liquid coatings on flat plates withdrawn vertically from a coating bath. We present three-dimensional (3D) two-phase flow simulations combining large eddy simulation (LES) and volume of fluid techniques. Three wiping configurations are simulated and the results are validated with experimental data from previous works. Multiscale modal analysis is used to analyze the dynamic interaction between the gas flow and the liquid film. In particular, we present a combination of multiscale Proper Orthogonal Decomposition (mPOD) and correlation analysis. The mPOD is used to identify the dominant traveling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet. This allows for revealing a two-dimensional mechanism for wave formation in the liquid coat. Finally, we use the numerical results to analyze the validity of some of the critical assumptions underpinning the derivation of integral film models of jet wiping.
11 citations
Abstract: We analyze the flow of a planar gas jet impinging on a thin film, dragged by a vertical moving wall. In the coating industry, this configuration is known as jet wiping, a process in which impinging jets control the thickness of liquid coatings on flat plates withdrawn vertically from a coating bath. We present three-dimensional (3D) two-phase flow simulations combining Large Eddy Simulation (LES) and Volume of Fluid (VOF). Three wiping configurations are simulated and the results are validated with experimental data from previous works. Multiscale modal analysis is used to analyze the dynamic interaction between the gas flow and the liquid film. In particular, we present a combination of Multiscale Proper Orthogonal decomposition (mPOD) and correlation analysis. The mPOD is used to identify the dominant travelling wave pattern in the liquid film flow, and the temporal structures are used to determine the most correlated flow features in the gas jet. This allows for revealing a two-dimensional (2D) mechanism for wave formation in the liquid coat. Finally, we use the numerical results to analyze the validity of some of the critical assumptions underpinning the derivation of integral film models of jet wiping.
10 citations
01 Jan 2004
TL;DR: In this paper, a simple one-dimensional model problem is used to introduce the concept of "leaky modes" which radiate energy and employ "perfectly matched layers" to solve such radiation problems.
Abstract: In a short introduction examples of open resonators with acoustic, electromagnetic, elastic and water waves are given. A simple one-dimensional model problem is used to introduce the concept of 'leaky modes' which radiate energy. Numerically we employ 'perfectly matched layers (PML)' to solve such radiation problems. In wave guide problems so-called 'trapped modes' can occur in addition to leaky modes. Trapped modes do not radiate energy and are therefore important in applications. A well known example are the 'Parker modes' in wind tunnel testing, heat exchangers or turbomachinery cascades. Finally, as an example of a two-dimensional open resonator we compute the resonances in a classical laser cavity. The acoustic analogon is the 'gap tone' problem which is of importance in airframe noise. Two examples of the latter, namely 'cavity noise' and 'slat noise' are discussed briefly. The latter is still part of ongoing research.
9 citations
TL;DR: In this paper, the optimal value of the preferred Strouhal number (Sd), which is used to determine the chamber length of a self-resonating nozzle, was experimentally studied at inlet pressures of 10 MPa and 20 MPa.
Abstract: Self-resonating pulsed waterjet (SRPW) is superior to plain waterjet in many ways and is being employed in numerous applications To further improve the performance of SRPW, the optimal value of the preferred Strouhal number (Sd), which is used to determine the chamber length of a self-resonating nozzle, was experimentally studied at inlet pressures of 10 MPa and 20 MPa The axial pressure oscillation peak and amplitude were used to evaluate the performance of SRPW, in order to find the optimum Sd value Results show that Sd value determines the self-resonance behavior of an organ-pipe nozzle and greatly affects the intensity of the axial pressure oscillation Under the experimental conditions, the optimum Sd values are 0315 and 0278 respectively, corresponding to inlet pressures of 10 MPa and 20 MPa Compared with the default value of 03 obtained from air jet experiment, the optimum Sd value at inlet pressure of 10 MPa is a little larger and oppositely a bit smaller at inlet pressure of 20 MPa Thus, if the inlet pressure is not considered, Sd value of 03 is reasonable for determining the chamber length of a self-resonating nozzle for generating effective SRPW
9 citations
References
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1,750 citations
TL;DR: The size specifications for suitable tracer particles for particle image velocimetry (PIV), particularly with respect to their flow tracking capability, are discussed and quantified for several examples.
Abstract: The size specifications for suitable tracer particles for particle image velocimetry (PIV), particularly with respect to their flow tracking capability, are discussed and quantified for several examples. A review of a wide variety of tracer materials used in recent PIV experiments in liquids and gases indicates that appropriately sized particles have normally been used. With emphasis on gas flows, methods of generating seeding particles and for introducing the particles into the flow are described and their advantages are discussed.
1,122 citations
TL;DR: In this paper, heat transfer characteristics of single and multiple isothermal turbulent air and flame jets impinging on surfaces are reviewed, and the effect of crossflow on impingement heat transfer is included.
935 citations
TL;DR: In this paper, the authors show that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance in a high-speed subsonic jet impinging on a flat plate.
Abstract: In a high-speed subsonic jet impinging on a flat plate, the surface pressure fluctuations have a broad spectrum due to the turbulent nature of the high-Reynolds-number jet. However, these pressure fluctuations dramatically change their pattern into almost periodic waves, if the plate is placed close to the nozzle (x0/d < 7·5). In the present study extensive measurements of the near-field pressure provide solid support for the hypothesis that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance. The feedback loop consists of two elements: the downstream-convected coherent structures and upstream-propagating pressure waves generated by the impingement of the coherent structures on the plate. The upstream-propagating waves and the coherent structures are phase-locked at the nozzle exit. The upstream-propagating waves excite the thin shear layer near the nozzle lip and produce periodic coherent structures. The period is determined by the convection speed of the coherent structures, the speed of the upstream-propagating waves as well as the distance between the nozzle and the plate. An instability process, herein referred to as the ‘collective interaction’, was found to be critical in closing the feedback loop near the nozzle lip.
436 citations
TL;DR: In this article, the authors focus on the design of small blower tunnels, and most of the information is applicable to wind tunnels in general, but most of their work is focused on wind tunnels with axial fans.
Abstract: Even with today’s computers, a wind tunnel is an essential tool in engineering, both for model tests and basic research. Since the 1930s, when the strong effect of free-stream turbulence on shear layers became apparent, emphasis has been laid on wind tunnels with low levels of turbulence and unsteadiness. Consequently most high performance wind tunnels were designed as closed-circuit types (Fig. 1(a)) to ensure a controlled return flow. However, as will be seen below, it is possible with care to achieve high performance from an open-circuit tunnel, thus saving space and construction cost. ‘Blower’ tunnels (with the fan at entry to the tunnel, Fig. 1(b)) facilitate large changes in working section arrangements; to cope with the resulting large changes in operating conditions, a centrifugal fan is preferable to an axial one. For ease of changing working sections the exit diffuser is often omitted from small blower tunnels, at the cost of a power factor greater than unity. This paper concentrates on the design of small blower tunnels but most of the information is applicable to wind tunnels in general.
398 citations