## 1 Introduction  
Geological exploration is an important means of identifying geological conditions, analyzing geological problems, and studying geological characteristics and laws of evolution, which play a key role in fields like engineering geology, hydrogeology, mineral investigation, and oil and gas exploration. Taking hydrogeological survey as an example, the causes, distribution, and movement patterns of groundwater and surface water could be obtained using this method, thereby providing a foundation for water evaluation and utilization [1]. In previous geological exploration, groundwater has often been overlooked, resulting in significant accidents. In hydrogeological surveys, activities such as collecting geological and hydrogeological data, conducting geophysical exploration and hydrogeological drilling, analyzing hydrogeological data, and simulating and predicting groundwater behavior, should be involved [2, 3]. Among these, drilling is one of the most commonly used techniques in hydrogeological surveys and is employed to obtain rock samples and create boreholes, thus providing crucial information about stratigraphic texture, formation properties, and groundwater levels. From the perspective of whether or not to obtain cores, drilling can be divided into coring drilling and non-coring drilling. By coring drilling, cores are obtained at target formations [4, 5], which serve as an important source of strata data in hydrogeological surveys. By testing and analyzing the cores, composition, structure, thickness, and properties of formation can be studied, and groundwater properties can be evaluated. With non-coring drilling, boreholes are drilled quickly and safely [6] to provide channels for groundwater collection and hydrological observation. Therefore, in hydrogeological surveys, both coring drilling and non-coring drilling are needed. During the drilling process, depending on the specific drilling purpose, it is sometimes needs to switch between the above two drilling methods. Currently, when switching between coring drilling and non-coring drilling, it is usually necessary to lift all the drilling tools out of the boreholes and replace the current drill bits with the appropriate ones. As the depth of boreholes increases, it will take a longer time to raise and drop the whole set of drilling tools in the boreholes, which reduces drilling efficiency, increases labor intensity, and raises drilling costs [7; 8; 9]. Thus, there is an urgent issue to be solved for switching between coring drilling and non-coring drilling without lifting the whole set of drilling tools. Previous studies on replacing drill bits without lifting all the drilling tools out of the borehole mainly focused on changing the diameter of the drill bit through special structures, which could not achieve the conversion between coring drilling and non-coring processes. In the literature [10], a drilling device for changing between coring drilling and non-coring drilling without lifting the drill pipes was designed. Based on the structure of wireline coring systems, it is only necessary to lift the inner tube assembly and replace the required drill bits when switching between coring drilling and non-coring drilling, which can improve drilling efficiency greatly. Based on that drill structure, a new modular bit for switching between coring drilling and non-coring drilling is proposed. During drilling, the drill bit is driven by rigs or downhole motors to rotate and break rocks in the borehole. While drilling, fluid is pumped into the boreholes to balance formation pressure, cool and lubricate the drilling tools, and remove rock cuttings in a continuous cycle. Drill bit structure will affect the cooling effect of drilling fluid. This is because varying flow field characteristics will be generated when drilling fluid flows in flow channels with different structures.