Numerical Study of Flow Control on Simplified High-Lift Configurations

Enhancement in the aerodynamic performance of wings and airfoils is very notable when Active Flow Control (AFC) is applied to Short Take-off and Landing aircraft (STOL). The present numerical study shows the application of steady, pulsed and synthetic tangential jets applied to the plain flap shoulder of a modified NASA Trapezoidal Wing. Pulsed jets are modeled by sinusoidal and square waveforms while synthetic jets are modeled only by pure sine waveform. The freestream airflow conditions are Mach number equal to ۰.۲ and Reynolds number equal to ۴.۳ million based on the mean aerodynamic chord. The presented simulations are two-dimensional and based on RANS for steady jet cases and URANS for pulsed and synthetic cases, compiled with the open-source suite SU۲ and adapted for time varying boundary conditions. Numerical results for modified configurations based on the same baseline wing profile considering different leading edges, jet slot height, flap position, blowing mass flow, type and frequency of the jets are presented. Curves of pressure coefficient distribution revealed a substantial influence upstream of the AFC, around the slat and main element. The jet slot height analysis showed that the lift gain is also influenced by the slot size due to the change of the local flow velocity considering the same blowing momentum coefficient. Regarding the jet frequency, no significant differences on the lift coefficients were found between the reduced frequencies F+ equal to ۱ and ۲. Results of aerodynamic loads showed an improved lift coefficient in relation to the baseline airfoil when pulsed and steady jets are employed. Pulsed jets under square waveform were effective even at high deflected flap condition at ۵۰°, with a significant gain in the lift coefficient of ۳۶%, in relation to the uncontrolled case, combined with a drag reduction of ۲۰%, and a decrease in mass flow up to ۴۹% in relation to the steady jet for the same lift gain. Although sine and square waveform results presented similar improvements for lift, the drag is around ۱۵% higher for the former. When compared with the steady jet case, the mass flow reduction is ۳۶% for the sinewave. Synthetic jets with zero-net-mass-flux proved superior to the baseline conventional multi-element airfoil only with deployed flap at ۵۰°, where a modest lift improvement of ۵% was observed.

Keywords:

Active flow control , Tangential jet , Steady jet , Pulsed jet , Synthetic jet , STOL aircraft