On the vorticity characteristics of lobe-forced mixer at different configurations

Abstract

Lobe-forced mixer is one typical example of the passive flow controllers owing to its corrugated trailing edge. Besides the spanwise Kelvin-Helmholtz vortex shedding, streamwise vortices are also generated within its mixing layer. The geometrical configuration of the lobe significantly affects these two types of vortices, which in turn affects the mixing performance of the mixer. In the present investigation, characteristics of mixers with five different configurations were examined and evaluated for two velocity ratios (r = 1, 0.4). The mixers have only one lobe in order to eliminate any possible interactions between neighboring vortices generated by the adjacent lobes. Hotwire anemometer was used to examine the Kelvin-Helmholtz vortices via the spectrum analysis while laser Doppler anemometer was employed to examine the streamwise vortices. It was found that there were two main frequencies for the Kelvin-Helmholtz vortices in the wake of the mixer; and the Strouhal numbers approached their respective maximum values at high Reynolds number. The rectangular mixer had similar mixing performance with the semicircular one; and both of them were better than the triangular mixer. The scalloping modification enhanced mixing by generating additional streamwise vortices while the scarfing modification could not improve the mixing performance. C I Mean streamwise circulation of the plane I, List of symbolse Penetration angle (half divergence angle) of the lobe-forced mixer k Wavelength of the lobe (m)

Effects of Core Flow Swirl on the Flow Characteristics of a Scalloped Forced Mixer

“…Two discrete vortex cores appeared at the x/D,, = 0.36 plane (SVl and SV2). Similar to the experiments of Mao et al [15], an additional streamwise vortex pair (SV3 and SV4) was also formed at x/D/, = 0.72 plane due to the effect of the scalloped notch. The length scale of this additional streamwise vortex pair was much smaller than the lobe height.…”

“…The core flow moved radially outward and the bypass flow moved radially inward. On the bypass side, the low shear region (between LM lines in yellow) was due to the low momentum fluid that accumulated in the lobe valley [15]. In addition, there was a triangle-shaped separation region (SP line in green) at the inlet plane of lobed mixer on the eore atid bypass sides due to the large penetration angle of this mixer.…”

“…Yu et al and Mao et al compared scalloped and unscalloped planar mixers with the same penetration angle and trailing edge profiles [13][14][15]. They showed that the streamwise vorticity was enhanced and its decay rate accelerated in scalloped mixers, largely because of the formation of two pairs of streamwise vortices at each lobe.…”

Parametric Effects on Internal Aerodynamics of Lobed Mixer-Ejector With Curved Mixing Duct

“…Recently, some researches were made for the advancement of lobed mixer contour, such as scalloping and scarfing of the lobes, lobe deflection, flow swirling, etc. Mao et al [23] compared scalloped and unscalloped planar mixers with the same penetration angle and trailing edge profiles. They showed that the streamwise vorticity was enhanced and its decay rate accelerated in scalloped mixers, largely because of the formation of two pairs of streamwise vortices at each lobe.…”

Effect of fuel injection with mixer in TBCC Hyperburner

“…al. [8][9][10] found that there exist a large scale secondary flow downstream the flow field in a lobed mixer from numerical simulation and experiments. Paterson [11] confirmed this discovery by experiments and p roposed a preliminary explanation of the mechanism.…”