# A New Flow Control Method of Slat-Grid Channel-Coupled Configuration on High-Lift Device
## 1 Introduction
In order to improve the lift-drag characteristics, grid flow channels can be added to the slats to improve the flow field in the slats. Grid fins [10], as multi-surface control systems consisting of an external frame and an internal grid partition, originate from the lift device composed of multiple elements used in the early design of aircraft, and have the advantages of high control efficiency, a large stall angle of attack, small hinge torque, and easy folding. In particular, their lift characteristics are good, and it is not easy to stall the devices with a high angle of attack, meaning they maintain good linearity. However, due to the defects in the structure, weight, resistance and technology of multi-element lift devices under the technical conditions of the time, single-element lift devices have been dominant in aircraft design for a long time. With the development of technology, the performance characteristics of grid fins derived from multi-element lift devices are increasingly understood, and their advantages as aerodynamic stabilizing and controlling surfaces for various types of aircraft continue to be highlighted. Research from Russia, the United States, Germany, and China has strengthened the understanding of grid fins; as a result, theoretical and applied achievements have been realized [11; 12; 13; 14; 15]. [PERSON] et al. [16] carried out a numerical simulation on four different slotting positions of wind turbine blades by means of a computational fluid dynamic method, and obtained the flow field and lift coefficient of the blades at different angles of attack. They found that, under high angles of attack, the jet formed by slots can effectively inhibit flow separation, and the aerodynamic performance was better when the slotting position was near the separation point. [PERSON] et al. [17] studied the aerodynamic characteristics of multi-element leading slat lift devices using the pressure measurement method and obtained a better leading slat scheme by comparing the influence of different configuration slats on the airfoil lift effect and aerodynamic efficiency. [PERSON] et al. [18] proposed a scheme of symmetrical slitting in the wind separation zone for the vertical axis wind wing NACA0012 studied, which delayed the separation of the airfoil boundary layer and improved the aerodynamic performance of the airfoil. [PERSON] et al. [19], taking the L1T2 three-element airfoil as the research object, proposed carrying out slot control on the leading-edge slat to slow down the boundary layer separation and reduce its impact on the wake. They focused on the slot location, the flow direction at the slot outlet, and the flow control technology in order to improve the stall characteristics of the lift enhancement device. Although there is a lot of research on the flow control of slats, most of this research focuses on the slot position and slot angle. There is relatively little optimization research on the slot layout scheme, slot width, and slot and chord angles of slotted airfoils of multi-element configuration, which limits the potential of the flow control effect of slats. In this paper, a grid-slat flow control configuration is proposed to increase lift, reduce drag and suppress flow separation. The quadratic curve parametric modeling method is used for the slot, and the design of the experiment aims to optimize its design. The optimal design parameters of the grid-slat configuration under the given design space and flow conditions are determined through numerical simulation. Moreover, the flow control mechanism of the optimal configuration and the influence and correlation of each design parameter on the lift-drag coefficient are analyzed. It provides a new idea and method for the design of three-dimensional grid multi-element airfoil lift devices in the future.