## 2 Experiment Setup and Model Configuration
### Experimental Setup for PIV Measurements  
In addition to the aerodynamic forces with a six-component force balance and the surface pressure measurements with the DSA pressure transducers, a particle imaging velocimetry (PIV) technique was employed to characterize the flow characteristics of the test models with and without control. The laser plane was located at the center of the seventh row of suction/jet holes, which were numbered from right to left in the span-wise direction (Figure 3). The experimental setup of PIV measurements is illustrated in Figure 1.  
During the PIV measurements, the incoming airflow was seeded with 1-5 \(\upmu\)m oil droplets by using a droplet generator. It was checked whether the seeding particles mixed thoroughly and uniformly or not (i.e., homogeneous seeding) during the experiments. The seeding density was found to be adequate for interrogation with interrogation regions of 32 \(\times\) 32 pixels. This kind of particle seeding has been a long established method. Identical fog machines, oils, and set-ups have been used in a number of previous studies (e.g., [18; 24; 25; 26; 27]). In addition, as proposed in [PERSON] and [PERSON] [28], that particle response could be well characterized by \(\tau\), the ratio of particle response time to the flow time scale (Stokes' number), and only particles with \(\tau\) > 0.05 were found to misrepresent the flow features. In the present experiment, \(\tau\) is estimated as: \(\tau=\tau_{p}/\tau_{f}=1.77\times 10^{-3}\), which is less than 0.05. Therefore, we believe the particle movement is able to represent the fluid velocity. Illumination was provided by a double-pulsed Nd:YAG laser (Vlite 200, Beamtech Optronics Co., Ltd., Beijing, China), which emitted two pulses of 200 mJ at the wavelength of 532 nm with a repetition rate of 2 Hz. The laser sheet was generated by a set of mirrors as well as spherical and cylindrical lenses, which can shape the emitting laser beam. In the measured region, the thickness of the laser sheet was about 1.0 mm. Using two independent laser arms, two laser sheets generated by one laser were manipulated to illuminate both the upper and lower sides of the test models. The laser energy was divided into two parts. This system was elaborately designed and carefully examined by the laser manufacturer. When the center of the target plane was about 1050 mm away from the lens of the laser arms, the laser energy reached the maximum. A 14-bit (1600 \(\times\) 1200 pixels) CCD (charge-coupled device) camera (pco.1600, PCO AG., Kelheim, Germany) was used to record images for the PIV measurements. The CCD camera and double-pulsed Nd:YAG lasers were connected to a workstation (host computer) via a Digital Delay Generator (Model 575-8C, Berkeley Nucleonics, San Rafael, CA, USA), which controlled the timing of the laser illumination and the image acquisition. The CCD camera was carefully aligned and was perpendicular to the laser planes using the spirit level. Figure 4: The distribution of pressure measurement taps. Instantaneous velocity vectors can be obtained by frame-to-frame cross-correlation operation of the images obtained by the PIV system. The MATLAB codes to process the PIV images were developed by the third author and [PERSON] of Iowa State University [18; 24; 26; 29]. There was another post-processing step for filtering/deletion of spurious vectors after image processing. However, the experimental results were maintained high-quality, as the valid vectors are mostly calculated to be about 98% in the present experiment. In the cross-correlation operation, a 32 \(\times\) 32 pixel interrogation window was adopted, with the interrogation window overlapped by 50%. When the instantaneous velocity vector (\(u\), \(v\)) in the flow field was determined, the corresponding span-wise vorticity \(\omega_{x}\) could be calculated.