A computational study is presented to characterize the flow behavior of independently controlled multiple synthetic jet actuators (SJA). For fixed geometric configuration and Reynolds number ([Formula: see text]) [Formula: see text], the influence of Strouhal number ([Formula: see text]) and phase difference [Formula: see text]) between the actuators on the evolution, and interaction of the vortices are highlighted. Directivity plots are employed to illustrate the effect of [Formula: see text] on the vectoring behavior of a synthetic jet array (SJ array). It has been observed that a high jet vectoring angle ([Formula: see text]) is achieved while operating the SJ array at low [Formula: see text]. The vectoring angle seems to be independent of [Formula: see text] for the low and high [Formula: see text]. However, for an intermediate [Formula: see text], the vectoring angle varies with the [Formula: see text]. The phase averaged vorticity contour for [Formula: see text] reveals that the evolution of the anti-clockwise vortex from the leading actuator (SJA1) decides the vectoring of the jet. By contrast, for higher [Formula: see text]([Formula: see text] and [Formula: see text]), the remnant vortices play a significant role in vectoring the jets toward the leading actuator. Based on the cross-stream distribution of time-averaged streamwise velocity, three distinct flow regimes are characterized: near-field, intermediate-field, and far-field. The strength of the jet is quantified by the downstream distribution of the jet momentum flux. Proper evolution of the vortices results in the enhancement of the jet momentum flux. It is recommended to operate the SJ array at an intermediate [Formula: see text] ([Formula: see text]) to vary the jet vectoring angle with phase differences as well as to achieve maximum jet momentum flux.
The study focusses on the response of a round synthetic jet (SJ) towards the Strouhal number and Stokes number An SJ is formed by issuing a stream of fluid into a low momentum region with the help of an oscillating boundary. The nature of the jet can be controlled by controlling the actuation frequency and amplitude of oscillation, and these two operating parameters are associated with the Strouhal number (St) and Stokes number (S) of the jet respectively. These non-dimensional numbers play a significant role in the effective utilization of SJs in controlling the flow, and heat transfer. The purpose of this article is to numerically investigate the flow behaviour of an SJ issued into a quiescent medium based on these two non-dimensional parameters. For analysis, a two-dimensional axisymmetric SJ is modelled using a finite volume solver integrated with openFOAM. The oscillating boundary resembles the motion of a diaphragm, and deforming mesh is enforced in the flow domain. Range of parameters within which the jet is operated: St – 0.13 to 0.16, and S – 23 to 36. The study highlights the strength, and spreading of the SJ based on St and S. Effect of St and S on the mean jet parameters such as centreline velocity decay, jet half-width, jet momentum flux, and entrainment rate are studied in detail, which can enhance the idea of operating an SJ effectively for better heat transfer and flow control. Time evolution of saddle point, and mean jet centreline decay profiles suggest the spacing between the orifice and a heated plate to be maintained for effective heat transfer. The jet should be operated at a low Strouhal number and high Stokes number for better impingement on a heated plate to be cooled. Low Strouhal number should be maintained to get high-velocity output, which is desirable for better flow control. These results are useful for the effective utilization of SJs for heat transfer, flow control, and other similar applications.
This paper highlights a direct numerical simulation study on the flow field of a coaxial synthetic jet (CSJ) generated from two independently controlled synthetic jet actuators, which are combined coaxially with [Formula: see text] orientation angle. The jet is issued into a quiescent environment from inner and annular openings (orifices) with equal hydraulic diameters, employing an oscillating boundary. Seven different mass flux ratios ([Formula: see text]) such as [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] are considered for the study. The average velocity ([Formula: see text]) of inner jet, measured at orifice exit, is kept at [Formula: see text] m/s (Reynolds number, [Formula: see text]), and the same is varied for the annular jet to achieve the desired [Formula: see text] s. The influence of [Formula: see text] s on the vortex rings, evolved from inner and annular orifices, along with their dynamics, is predicted by furnishing the instantaneous flow field. Also, we examine the effect of [Formula: see text] s on the mean flow parameters of the CSJ. Moreover, the CSJ flow field is compared with the inner cavity synthetic jet (SJ), and annular cavity SJ under identical conditions, to demonstrate the superior performance of the CSJ over the single cavity SJs. For CSJ, the azimuthal instability of the evolved vortex rings can be triggered by decreasing the [Formula: see text], which results in a wide jet. For [Formula: see text], the CSJ retains its axisymmetric nature, and the interaction of vortex rings emanating from the inner and annular cavities influences the strength and spreading of the CSJ. The modal decomposition of the instantaneous flow field is also performed using proper orthogonal decomposition method to gain insight of the coherent vortical structures present in the modes. The study will be useful for deploying such novel coaxial synthetic jets in various applications.
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