Aerospace Science and Technology 107 (2020) 106268 Contents lists available at ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte Effect of forcing the tip-gap of a NACA0065 airfoil using plasma actuators: A proof-of-concept study Christian Anzalotta 1 , Kamlesh Joshi 2 , Erik Fernandez 3 , Samik Bhattacharya ∗,4 University of Central Florida, Orlando, FL 32816, United States of America a r t i c l e i n f o a b s t r a c t Article history: Received 1 July 2020 Received in revised form 1 October 2020 Accepted 5 October 2020 Available online 14 October 2020 Communicated by Muguru Chandrasekhara Keywords: Tip-leakage vortex Plasma actuator Flow control A proof-of-concept study is presented to understand the effect of continuous forcing by a dielectric- barrier-discharge (DBD) plasma actuator on the strength of the vortices formed in the tip-gap of a single NACA0065 airfoil. The airfoil was mounted with variable tip gaps in the test-section of a suction-type wind tunnel. Continuous forcing was generated by mounting a straight DBD actuator in the tip gap. The flow field was investigated experimentally by dynamic-pressure measurements, and stereoscopic-particle- image-velocimetry (SPIV). In addition, URANS was performed to investigate the flow field in the tip gap region, where SPIV could not be conducted. The results showed that the effectiveness of forcing decreased with increasing tip-gaps and free-stream velocity. The maximum cancellation of the vortex was observed when the blowing ratio was approximately 0.93, with a tip gap of 0.02c (c = chord) and free stream velocity of 2.7 m/s. Both experimental and numerical results showed that in this particular case, the DBD actuator created a strong reverse flow opposing the direction of tip flow. This reverse flow altered the pressure gradient in the tip gap region and canceled the vortex altogether.  2020 Elsevier Masson SAS. All rights reserved. 1. Introduction Tip-leakage vortices (TLV’s) can form in the gap created be- tween a wall and the tip of an airfoil. They form due to the leakage of flow caused by the pressure difference from the pressure side to the suction side of the airfoil. TLV’s cause total-pressure losses in turbo-machinery rotors, and can reduce the efficiency of a turbo machine [1–4]. Hence, many researchers have attempted to cancel or reduce this vortex by using both passive and active flow control. Douville et al. used a squealer tip and a plasma actuator to con- trol the flow in the tip gap of a turbine cascade and showed that the control efficiency of the plasma actuator was largely depen- dent on the unsteady frequency of its operation [5]. Zhang et al. investigated the effect of plasma actuation on the tip leakage flow with respect to a compressor cascade model. They concluded that * Corresponding author. E-mail address: samik.bhattacharya@ucf.edu (S. Bhattacharya). 1 Graduate, Mechanical and Aerospace Engineering Department, University of Central Florida, Orlando, FL, 32816, and AIAA Student Member. 2 Graduate Research Assistant, Mechanical and Aerospace Engineering Depart- ment, University of Central Florida, Orlando, FL, 32816. 3 Assistant Professor, Center for Advanced Turbomachinery and Energy Research, Orlando, Fl, 32826, and AIAA Member. 4 Assistant Professor, Mechanical and Aerospace Engineering Department, Univer- sity of Central Florida, Orlando, FL, 32816, Orlando, Fl, 32826, and AIAA Member. it was the improvement of axial momentum which was a major factor in suppressing the compressor tip leakage flow [6]. Akturk and Camcy used a number of novel tip treatments to control the tip gap flow in an axial flow fan. By using stereo PIV to measure the three-dimensional mean flow observed near the blade tip, they demonstrated significant gains in the axial mean velocity when a proper pressure side tip extension is used [7]. In a follow-up work Akturk and Camci elaborated the tip clearance gap effects with regards to real-world applications in VTOL UAVs and again demonstrated improved performance of the ducted fan [8]. Mat- sunuma and Segawa implemented a string-type and a ring-type design for the plasma actuator and demonstrated reduction of tip- leakage flow in a low-pressure turbine blade [9]. Shavalikul and Camci used RANS based viscous flow simulations showed that a tip platform extension can result in a significant decrease in the tip leakage loss [10]. Curtis et al. demonstrated tip-leakage control using active blowing by an air curtain [11]. However it has still been difficult to completely cancel the TLV’s. Moreover, compared to passive forcing, active forcing has received less attention in this area. Hence it is still worth studying the physics of such TLV’s be- ing perturbed by active forcing. In the present work, we perform a proof-of-concept experiment where we created a tip-gap between a single NACA 0065 airfoil and the tunnel floor. Then we fixed a DBD plasma actuator on the floor of the wind tunnel in the tip- gap. We study, both experimentally and numerically, the effect of active forcing using DBD plasma actuators on TLV’s. https://doi.org/10.1016/j.ast.2020.106268 1270-9638/ 2020 Elsevier Masson SAS. All rights reserved.