A general correlation for the stagnation point Nusselt number of an axisymmetric impinging synthetic jet

Abstract

Whereas the heat transfer mechanisms in steady impinging jets are well understood, the available knowledge of heat transfer to impinging synthetic jets remains inconsistent. This paper provides an objective comparison of the stagnation point heat transfer performance of axisymmetric impinging synthetic jets versus established steady jet correlations. Furthermore, a general correlation for the stagnation point Nusselt number is proposed including the effect of all appropriate scaling parameters: Reynolds number (500 ≤ Re ≤ 1500), jet-to-surface spacing (2 ≤ H/D ≤ 16) and stroke length (2 ≤ /D ≤ 40). Based on the ratio of stroke length to jet-to-surface spacing L L 0 0 /H, four heat transfer regimes are identified.

Flow regime characterisation of an impinging axisymmetric synthetic jet

“…Valiorgue et al [8] presented flow visualisation and heat transfer data which explored the influence of stroke length relative to nozzle to surface spacing on flow regimes and convective heat transfer mechanisms for an 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 5 impinging synthetic jet but the study was limited to small jet to surface distances. Persoons et al [13] have extended these findings for a more comprehensive range of parameters however no flow measurements were performed. Their study also gives an objective comparison of the stagnation heat transfer coefficient behaviour of an axisymmetric impinging synthetic jet and correlations and data for equivalent steady jets from a number of different sources.…”

“…Comprehensive reviews of heat transfer to impinging synthetic air jets have been conducted by Persoons et al [13], Gillespie et al [14], Wang et al [15], Pavlova and Amitay [16], Travnicek and…”

“…The synthetic jet impinges onto a surface consisting of a heated copper plate (450550mm 2 ,5mm thick) approximating a uniform wall temperature boundary condition as verified in previous studies [13,26]. Heating is provided using a 1.1mm thick silicon heater mat which is adhered to the underside of the plate on one side and insulated on the other.…”

“…8b shows that the stroke length at which maximum impingement velocity occurs roughly scales with the nozzle-to-surface distance. To visualise this, the data are plotted by recasting the stroke length in the form used by Persoons et al [13] to identify heat…”

A new method for fluid input into a hybrid synthetic jet actuator

“…The outgoing fluid is responsible for formation of the coherent vortical structures in the immediate vicinity of the nozzle exit. The large vortex structures and higher jet velocities increasing the Reynolds number lead to an augmentation a e-mail: kordik@it.cas.cz of convective heat transfer of the jet [13,6,25] and removal of the already heated (or cooled) fluid from the neighborhood of the heat transfer surface. This is the reason why the HSJAs producing non-zero-net-mass-flux have a great potential in heat transfer applications, even greater than common SJs (this was confirmed experimentally in [13]).…”