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... [31]. Amitay et al. [52] used a synthetic jet rectangular orifice width of 0.5 mm. Crook et al. [41] experimented on jets with a circular orifice diameter of 0.5 mm, while that used by Holman et al. =-=[53]-=- had a diameter of 2 mm. In water, Crook and Wood [26] used synthetic jets with orifices of 5 and 7 diameters. More extensive testing of synthetic jets was done by Mohseni and colleagues [48, 27, 28]....

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...respect to the heated surface. Two prime orientations of the jet have been considered, namely, perpendicular and cross jet impingement on the heater. It is found that if jet is placed at an optimum location in either impingement or cross flow position, it can provide similar enhancement. Keywords: synthetic jets, electronics cooling, thermal management, impingement, jet design INTRODUCTION Synthetic jets have been routinely investigated from the standpoint of flow control [1, 2, 3, 4], thrust vectoring of jets [5], triggering turbulence in boundary layers [6,7], and heat transfer applications [8, 9, 10]. In case of heat transfer applications, the ded From: https://proceedings.asmedigitalcollection.asme.org on 06/29/2019 Terms of Uscooling process can either be facilitated by direct impingement of vortex-dipoles on heated surfaces [11,12] or via employing the jets to enhance the performance of existing cooling circuits [13]. In view of these applications, the jet performance can be assessed with various methodologies. Integral analyses of the time-and-spatially-dependent jet exit velocity profiles serve to quantify the jet performance in terms of the net momentum/energy flux effectively [4,14...

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...strength of each vortex shed has been shown bysDidden [3] to be related to the flux of vorticitysthrough a (x, y) planar slice of the orifice during thesejection phase of the cycle. Holman & Utturkar =-=[4]-=-sdetermined that jet formation is directly related tosthe flux of the vorticity from the synthetic jet. Thesbreakdown of the turbulent jet flow tends to occursas a result of spanwise instabilities of ...

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...sasin2πft for a synthetic jet and u = Uc0 for a continuous jet) is applied at the slot, and a constant static pressure condition, p = 0 Pa, is applied at the inlet and outlet of the duct. Furthermore, a non-slip condition is imposed at the surfaces of solids (the rectangular cylinder, beak on the slot, and side walls). The results calculated under the velocity conditions Us0 = Uc0 = 7.5 m/s (Re = 2480) are presented, where Us0 is given the spatial and time-averaged velocity of the only discharge flow over the cycle at the slot exit, which is defined in accordance with a preceding study Holman [3]. RESULTS AND DISCUSSION The experimental and numerical results obtained under the conditions ε = ±0.5, Re = 2480 (Us0 = 7.5 m/s for a synthetic jet, Uc0 = 7.5 m/s for a continuous jet), H = 300 × 10 −3 m, C = 5, b0 = 5 × 10 −3 m are discussed. Figures 4–9 show typical flow patterns around the rectangular cylinder with an asymmetric slot for continuous or synthetic jets in a duct. Flow visualizations by the smoke wire method (1/13 s) are shown in (a); (b) and (c) show the timeaveraged velocity vectors and time-averaged pressure distributions, respectively, obtained by numerical simulations. Th...

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...the fluid stream in heat sink’s flow passage and perform periodic impingement on the heated wall. The operation over one diaphragm cycle is such, the jet delivers an intense momentum fluid outflow with zero net mass output through the orifice, hence complying with “synthetic jet” or Zero-NetMass-Flux jet condition. The vortex formation associated with synthetic jet is governed by the non-dimensional groups Reynolds number (Re) and Stokes number (S), and occurs under the parametric condition of Re/S2>K, where the constant K ≈ 1 for two-dimensional jets and 0.16 for axisymmetric synthetic jets (Holman et al., 2005). Through due consideration of this requirement, the geometrical dimensions were selected for the 2-dimensional analytical model attempted. They are: orifice width do = 50 μm, orifice length ho = 50 μm, channel height H = 500 μm, channel length D = 2250 μm, heater length L = 750 μm, cavity width dc = 750 μm and cavity height hc = 500 μm. This selection was checked for its compliance with the continuum mechanics for the scale of the attempted problem using Knudsen number Kn, which is the ratio of the molecular free path length to representative length. 2.2 Governing equations This study investi...

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...ing and suction alternately form vortex pairs or vortex rings near the exit and generate a velocity distribution and actual flow similar to those of a continuous jet by entrainment downstream, even though the time-averaged velocity and flow rate are zero at a nozzle exit. Over the past few decades, many experimental and numerical studies [10] have been conducted on synthetic jets, and their onset conditions and structure have been discussed. For example, Holman et al. indicated that the formation of a synthetic jet is governed by K (the ratio of Reynolds number to the square of Stokes number) [3]. Koso and Kinoshita investigated the differences in flow characteristics such as velocity profile, entrainment and momentum between continuous jets and synthetic jets [5]. However, little is known about the detailed structure of the jet and the relation between flow characteristics and fluid force. Especially, the Coanda effect of a synthetic jet near a rigid boundary has not been thoroughly investigated [8]. In the present study, we conducted experiments and numerical simulations to clarify some of the fundamental flow characteristics of synthetic jets near a rigid boundary and a synthetic j...