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Abstract
To control the flow separation in the compressors, a novel pulsed jet concept without external energy injection is proposed. The new concept designs a slot in the middle of the blade and sets a micro device to switch the slot periodically. Such a structure is expected to generate a pulsed jet by the pressure difference between the pressure side and the suction side of the blade. In order to analyze the interaction between the pulsed jet and unsteady separated flow, our numerical and experimental study is based on a specific cascade (with a flow separation inside) and a pulsed jet (one of the unsteady flow control method). The experimental and numerical results both show that when the frequency of pulsed jet is approximate to that of the separation vortex, then the control tends to be more effective. Based on the numerical simulations, the proper orthogonal decomposition (POD) is then used to reveal the control mechanism, extracting the different time-space structures from the original field. The results with the aid of POD show that the pulsed jet can redistribute the kinetic energy of each mode, and strengthen or weaken certain modes, particularly, while the steady jet reduces the kinetic energy of high-order modes in whole. Also, pulsed jet with proper parameters can transfer the energy from higher modes to the first flow mode (averaged flow), which is due to the conversion of the spatial vortical structures and the time evolution of the modes.
Highlights
Flow separations are always related to drag increase, lift, and kinetic energy losses, and so on.Many researchers have long been preoccupied with finding the solutions with the declining flow separation
There is no unifying in-depth background on the unsteady control mechanism; for example, some interpreted it as an influence between the separation vortex and vortex pair that is induced by the pulsed jet [11]
The complex coupling of trans-scale vortical structures makes the unsteady control mechanism difficult to reveal, so it is necessary to establish a reduced-order model [20] or to employ a method to extract the useful information from the flow field, such as proper orthogonal decomposition (POD) method
Summary
Flow separations are always related to drag increase, lift, and kinetic energy losses, and so on. This paper presents a novel implementation to control the flow separation in the high load compressors, using the unsteady control method in order to decrease the energy cost for flow control. There is no unifying in-depth background on the unsteady control mechanism; for example, some interpreted it as an influence between the separation vortex and vortex pair that is induced by the pulsed jet [11] Some attribute it to reasonably organizing different coupling vortices in the flow field [19]. The complex coupling of trans-scale vortical structures makes the unsteady control mechanism difficult to reveal, so it is necessary to establish a reduced-order model [20] or to employ a method to extract the useful information from the flow field, such as proper orthogonal decomposition (POD) method.
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