Dynamic stall control of a S809 airfoil is numerically investigated by implementing a co-flow jet (CFJ). The numerical methods of the solver are validated by comparing results with the baseline experiment as well as a NACA 6415-based CFJ experiment, showing good agreement in both static and dynamic characteristics. The CFJ airfoil with inactive jet is simulated to study the impact that the jet channel imposes upon the dynamic characteristics. It is shown that the presence of a long jet channel could cause a negative effect of decreasing lift and increasing drag, leading to fluctuating extreme loads in terms of drag and moment. The main focus of the present research is the investigation of the dynamic characteristics of the CFJ airfoil with three different jet momentum coefficients, which are compared with the baseline, giving encouraging results. Dynamic stall can be greatly suppressed, showing a very good control performance of significantly increased lift and reduced drag and moment. Analysis of the amplitude of variation in the aerodynamic coefficients indicates that the fluctuating extreme aerodynamic loads are significantly alleviated, which is conducive to structural reliability and improved life cycle. The energy consumption analysis shows that the CFJ concept is applicable and economical in controlling dynamic stall.

Improved delayed detached eddy simulation is performed to investigate aero-optical distortions induced by Mach 0.5 flow over a cylindrical turret with a flat window at a Reynolds number of Re = 5.9 × 10⁵ based on the turret radius. Optical wave-front distortions and associated far-field intensities at elevation angles of 90°, 100°, and 120° are calculated using the geometric ray-tracing method and Fourier optics theory, respectively. The time-averaged properties of the flow fields and the optical distortions are compared with the experimental results, and reasonable agreements are obtained. It is shown that large-scale coherent structures significantly increase the optical distortions and, consequently, degrade the optical performance in terms of the far-field intensity level, while the optical effects of the attached turbulent boundary layers and separation bubbles are trivial and negligible. Very little difference is observed in both instantaneous and statistical optical results calculated with and without defocus and astigmatism components, indicating the adequacy of the removing piston and tilt components for aiding in the design of adaptive optical systems. Both co-flow and blowing jet fluid control methods are introduced with a steady mass flow to alleviate wave-front distortions, and preliminary simulations demonstrate the practicability of these fluid control methods in suppressing the optical distortions. It is shown that both the active control methods are competent to reduce the overall wave-front root-mean-square of the optical path difference.

This study presents the magnetized hybrid nanofluid flow with heat source/sink over an exponentially stretching/shrinking sheet. Slip conditions are implemented to analyze the hybrid nanofluid flow for both slip and no-slip conditions. Additionally, the hybrid nanofluid of alumina and copper (hybrid nanoparticles) with blood (base fluid) has been considered and discussed with both suction and injection parameters. The appropriate similarity variables are used to convert partial differential equations (PDEs) into ordinary differential equations (ODEs) and solved analytically with the help of the homotopy analysis method (HAM). The impact of different embedded parameters has been shown in the form of graphs and tables. The numerical values of skin friction and Nusselt number are presented in the form of Tables for both slip and no-slip cases. It is summarized that the upsurge of the velocity slip parameter and magnetic parameter increases the skin friction, while the rising of the thermal slip parameter and heat generation parameter decreases the Nusselt number.

A comparative study of two combined blowing/suction flow control methods was conducted on the pitching airfoil using the unsteady Reynolds-averaged Navier–Stokes (URANS) method. One used leading-edge blowing and trailing-edge suction, which is referred to as a co-flow jet (CFJ), and a conformal slot CFJ (C-CFJ) was adopted. Another used leading-edge suction combined with trailing-edge blowing, which was called reversed CFJ (R-CFJ). The S809 airfoil was used as the baseline as its stall characteristic is suitable for separation flow or stall control research. Aerodynamic coefficients of these two combined blowing/suction methods were compared under no-stall, mild-stall, and deep-stall cases. The net gain of output power was also discussed if CFJ methods were used for wind energy applications. The influence mechanism of these two methods on the flow around the airfoil was revealed. The results showed that the C-CFJ is suitable for the no-stall and mild-stall cases, while the R-CFJ is suitable for the deep-stall case. Leading-edge suction is more stable than leading-edge blowing when suppressing the dynamic stall. The leading-edge jet flow will cause dynamic stalls when it is detached from the airfoil surface, while the detached jet flow can block the development of the separation when it is placed on the trailing edge.

A new partial circulation control (PCC) method is implemented on the blunt trailing edge DU97-Flatback airfoil, and compared with the traditional full circulation control (FCC) based on numerical analysis. When the Coanda jet is deactivated, PCC has an attractive advantage over FCC, since the design of PCC doesn’t degrade aerodynamic characteristics of the baseline flatback section, in contrast to FCC, which is important in practical use in case of failure of the circulation control system. When the Coanda jet is activated, PCC also outperforms FCC in several respects. PCC can produce much higher lift coefficients than FCC over the entire range of angles of attack as well as the entire range of jet momentum coefficients under investigation, but with slightly higher drag coefficients. The flow field of PCC is less complex than that of FCC, indicating less energy dissipation in the main flow and hence less power expenditure for the Coanda jet. The aerodynamic figure of merit (AFM) and control efficiency for circulation control are defined, and results show that PCC has much higher AFM and control efficiency than FCC. It is demonstrated that PCC outperforms FCC in terms of effectiveness, efficiency and reliability for flow control in the blunt trailing edge wind turbine application.

Two-dimensional flow of the pulsed co-flow jet (CFJ) and the influence of the pulsed parameters on the lift and power consumption are investigated numerically. Firstly, the jet channel of traditional CFJ airfoil is improved. The stall margin is increased by 3° compared with the corresponding traditional CFJ airfoil, and the lift is increased, while the drag is reduced significantly. Then, the influence of the pulsed parameters, such as the pulse waveform, including sinusoidal and rectangular waves, the duty cycle, and the pulse frequency on the lift and power consumption are presented and analyzed in detail. It is concluded that, compared with the steady CFJ, the pulsed CFJ possesses much better ability in suppressing separation and can improve the lift characteristics significantly with limited cost of power consumption. For example, at an angle of attack of 20° flow separation occurs severely, when the steady CFJ is adopted; however, the airflow becomes fully attached on the upper airfoil, when the rectangular pulsed CFJ is employed. As a result, the lift corresponding to the rectangular wave is higher than that of the sinusoidal wave. The results also indicate that the lower duty cycle and pulse frequency can lead to the higher lift but with more power consumption.