Time-Resolved Analysis of Circulation Control over Supercritical Airfoil using Digital Particle Image Velocimetry (DPIV)
Hussain, Mian M.
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Active pneumatic flow control methods as applied to aerospace applications have shown noteworthy improvements in lift compared to traditional means. The General Aviation Circulation Control (GACC) concept currently under investigation at NASAâ s Langley Research Center (LaRC) is an attempt at addressing some of the fundamental obstacles related to the successful development and implementation of such techniques. The primary focus of research in the field of high lift pneumatic devices is to investigate ways of obtaining significant improvements in the lift coefficient without resorting to moving surfaces. Though it has been demonstrated that the lift coefficient can be amplified in a variety of ways, the chosen method for the current work is via enhanced circulation stemming from a trailing edge Coanda jet. A secondary objective is to reduce the amount energy expenditure used in these pneumatic techniques by implementing time-variant flow. This paper describes experimental observations of the flow behavior at the trailing edge of a modified water tunnel based supercritical airfoil model that exploits both steady and pulsed Coanda driven circulation control. A total of 10 sets of data, excluding a baseline case of no Coanda jet, were sampled with five cases each for steady and pulsed flow, the latter at a reduced frequency, f+, of 1. Two cases of equal momentum coefficient but with varying forced frequencies were isolated for further study in an attempt to accurately compare the resultant flow dynamics of each method. All measurements were taken at a zero-lift angle of attack by means of a non-invasive time accurate flow visualization technique (DPIV). Vorticity behavior was investigated using TecplotÂ® and a MATLABÂ® program was developed to quantify the Strouhal Number of time-averaged velocity fluctuations moving aft of the Coanda surface for each case.
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