Improved delay detached eddy simulation is performed to explore the flow features and aero-optical effects of turrets with different bottom cylinder height at a freestream Mach number Ma = 0.7. Analysis of both the time-averaged and instantaneous flow features demonstrate that the shock motion causes the oscillation of separated shear layer. In flow analysis, two unsteady shock-wake-correlated modes are discerned: the asymmetric shifting mode and the symmetric breathing mode. With the increase of cylinder height, the relative energy of shock gradually increases, which goes from 26% to 59%. The proper orthogonal decomposition analysis yields the single frequency peak for the two dominant modes. The frequency peaks of shifting mode are generally at St_D < 0.23, while the frequency peaks of breathing mode are generally at St_D > 0.26. The dynamic mode decomposition analysis gives range of frequency peak. The frequency peaks of shifting mode are in the range of St_D = 0.11–0.23, and the frequency peaks of breathing mode are in range of St_D = 0.26–0.41. Optical distortion analysis indicates that the distortion calculated in five cases is linked to the breathing mode. When the beam passes through the turbulent wake, it exhibits the high-frequency and high-amplitude characteristics.

One of the primary challenges in developing higher-power laser systems is the aero-optical thermal blooming effect that occurs during laser beam propagation through the inner channel. This effect refers to the phase distortion and degradation of far-field beam quality due to the uneven changes in temperature and density of the flow field within the channel as the gas medium absorbs the laser's energy. Currently, there is still a lack of high-accuracy and systematic coupling numerical simulation method for the study of the thermal effect. In this study, thermal blooming effect was calculated and analyzed based on the research framework of the coupling of light field and flow field. Differences between the geometric ray tracing method and the linear integration method in calculating the wavefront distortion were compared, which proved that the approximate treatment of beam’s rectilinear propagation can be used to deal with the case discussed. The wavefront distortion was fitted by Zernike polynomial, and the distortion level and its influence on far-field intensity characteristics were analyzed in combination with adaptive optical correction. The results indicated that without adaptive optical correction, significant wavefont distortion developed within 0.5 seconds and increased approximately linearly with time. Matintaining the ratio of pipe radius to beam radius greater than 1.5 can effectively reduce the thermal blooming effect. Adaptive optical correction reduced wavefront distortion by about 70%. The affects of phase modulation from inner-channel wavefront distortion and far-field transmission led to substantial light intensity reduction and spot diffusion over long propagation distances without improvement measures. Adaptive optical correction can signifingntly improve far field beam quality. Therefore, optimization of laser transmission channel geometry and adaptive optics correction are effective approoches to reduce the thermal effect.

Improved Delayed Detached Eddy Simulation (IDDES) is used to calculate the flow field around the turret in transonic flow. The ray tracing method is employed to calculate the aero-optical effect at different beam emission angles. The aero-optical effect affected by different flow structures is analyzed. The results indicate that the pressure distribution on the turret exhibits two main characteristics: a symmetric “breathing mode” and an antisymmetric “shifting mode”. Their peak frequency are at 0.26–0.41 and 0.11–0.22, respectively, and these two main features exhibit coherence in the frequency. The drag force of the turret is primarily determined by shear layer oscillation, the lateral force is largely due to the shock wave jitter, and the axial force is influenced by both shock wave jitter and shear layer oscillation. The high-order Optical Path Difference (OPD) is relatively small with little fluctuation when the beam passes through the attached flow region. However, when the beam traverses the shock wave region and the turbulent wake zone, the high-order OPD is significantly large, with the time-averaged OPD being about four times that of the attached flow region, and the peak OPD being 13 times greater than that of the attached flow. The high-order OPD of the beam passing through the shear layer and turbulent wake vortices shows similar energy ratio using Proper Orthogonal Decomposition (POD) analysis. In contrast, the OPD energy of beams passing through the shock wave is more concentrated in the first five modes.

In this paper, unsteady numerical simulation of jet Circulation Control (CC) is carried out with the NACA0012-CC airfoil as the research object. The dynamic process from the opening of jet slot and adjustment of jet intensity to the stable state of jet control effect is explored. The time-delay effect and flow mechanism of jet are analyzed. The mechanism of jet momentum coefficient and moment coefficient fluctuating with time is revealed. The fluctuation of jet momentum coefficient is caused by the change of the pressure coefficient distribution on the Coanda surface or the structure of the wave system inside the jet, and the oscillation frequency of the wave system structure of the under-expansion supersonic jet reaches 1481 Hz at the opening moment. Based on the aerodynamic model and Proportional-Integral-Derivative (PID) control theory, the closed-loop control system of CC airfoil is designed. The parameters of PID control system are adjusted by the Genetic Algorithm (GA), which significantly improves the response ability of the control system to step, ramp and sine signals, and improves the dynamic performance of the system. Aimed at the special time-delay effect of jet control, Long Short-Term Memory (LSTM) neural network module is added to the control system to predict the target input signal, which strengthens the prediction ability of GA-PID control system to the target signal at the next time moment. By using LSTM neural network correction, the control hysteresis caused by jet time-delay effect is alleviated, and the response ability of the control system is effectively improved. Finally, the designed LSTM-GA-PID control system is applied to the NACA0012-CC airfoil for the pitch control simulation test. The test results show that the control system designed in this paper has good dynamic performance and can respond quickly and accurately to complex input signals, which confirms the effectiveness of the control system.

Aiming at the problem of dynamic stall of helicopter rotors under variable free stream during forward flight, a dynamic stall control method of airfoils based on the co-flow jet (CFJ) is developed. Taking NACA0012 airfoil as the research object, the unsteady Reynolds-averaged Navier-Stokes equations are solved based on the transition SST turbulence model, and numerical simulations of the dynamic stall of airfoils controlled by CFJ under different parameters are carried out. The results show that CFJ can effectively suppress the dynamic stall of airfoils. Under the condition of variable free stream, the jet channel has a negative impact on the original aerodynamic characteristics of the airfoil, and the power coefficient increases much faster than the jet momentum coefficient. There is an optimal working condition for CFJ to achieve the best control effect. CFJ accelerates the evolution of multi-vortex by mixing with the mainstream to suppress the dynamic stall, and enhances the kinetic energy of the chordwise flow to overcome the adverse pressure gradient to suppress flow separation and promote flow reattachment. Under the condition of Mach number 0.283, reducing frequency 0.151 and advance ratio 0.25, CFJ can increase the lift of the airfoil, reduce the drag and the negative pitching moment peak, and advance the reattachment of the flow. The overall aerodynamic characteristics of the airfoil are obviously improved by the CFJ control.

Delayed detached eddy simulation (DDES) is used to simulate the flow field around the conformal optical window turret and the flat optical window turret. The aero-optical effect and the far-field diffraction result of the two optical windows at 0°, 90° and 180° angles are quantitatively analyzed based on the flow field around the turret. Zernike polynomial is applied to fit the wavefront distortion, and the adaptive optics is used to analyze the propagation performance of the two optical windows. The results show that the beam transmission performance of the flat optical window is better than that of the conformal one at the angles of 0° and 180° without adaptive optical correction, while the beam transmission performance of the conformal window at 90° angle is better than that of the flat one. When the adaptive optics correct these low-order terms including piston, tilt, defocus and astigmatism, the beam transmission performance of the conformal optical window is better than that of the flat one at the angles of 90° and 180°. At the angle of 0°, the beam transmission performance of the two optical windows is similar. With the increase of the angle, the high-order terms of the two windows decrease continuously. It is worth noting that the peak intensity of the distorted beam after diffraction in the far field may be larger than that of the undistorted beam in the far field. Meanwhile, the location of the peak intensity will be seriously offset.