Research On Drag Reduction Of Blades With Bionic Non-Smooth Surfaces In Hydrodynamic Torque Converter

Hydrodynamic torque converter is a kind of device works between transmission and engine widely used for power transmission in automobile and engineering machinery and other industries with the advantages of load adaptation and can improve the stability etc. The biggest disadvantage of hydrodynamic torque converter is the low efficiency and it always faces challenges that it was replaced by gear on the ship and replaced by the electric transmission on the locomotive and now is challenged by CTV, DCT in automatic speed changing of cars, and is threatened by static fluid in engineering machinery, so it is of great significance to increase its efficiency.The viscosity of fluid will arise boundary layer on the blade surface when the fluid flows through the blade surface of hydrodynamic torque converter. There is the process of turbulence burst in boundary layer and plenty of energy will lose. Otherwise, boundary layer separation and secondary flow etc. due to viscosity effect can cause flow loss of hydrodynamic torque converter which affects the performance and efficiency of the torque converter. Therefore, controlling the flow in boundary layer and restraining the turbulent burst can improve the efficiency of torque converter and reduce the energy loss effectively and reduce the flow resistance and energy loss of the fluid in the torque converter especially in boundary layer. This paper researched the streamlined blade of hydrodynamic torque converter on restraining the turbulent burst on the bionic non-smooth surface and controlling boundary layer flowing to realize drag reduction. The main summaries are as follows:1. Calculation for transient flow of internal flow in the hydrodynamic torqueconverterFirstly, the experiment was used to check the validity of the calculation method for transient flow of internal flow in the hydrodynamic torque converter CFD and used the same CFD mechanism to evaluate the of drag reduction effect and analyze the mechanism. DSL(Dynamic Smagorinsky-Lilly) model of LES was used to set the no slipping boundary conditions, use the structured grid and set appropriate parameters. Comparing the simulation data and experimental data on YJ315 hydrodynamic torque converter, the maximum error of torque ratio is 1.45%, the maximum error of the efficiency is 4.5%, and the maximum error of capacity coefficient is 13.86%. The maximum errors of torque ratio and efficiency are less than 5%. The high calculation accuracy proved the validity and correctness of the numerical simulation method.2. Blade bionic non-smooth design and non-linear optimizationThe bionic structure of bionic groove and mastoid structure were designed on the surface based on the flow states of different surfaces of YJ315 hydrodynamic torque converter stator blade. The surface microstructures of shark, eagle, seal and shell which with good drag reduction effect are selected as biological archetype and four bionic grooves of different shapes was designed on the blade suction surface. Bionic rose mastoid structure was designed on the blade pressure surface to form hydrophobic surface. The numerical simulation of the flow field with the groove bionic blade is made. The result shows that L-shaped groove(seal surface microstructure) has the best drag reduction effect and the drag reduction rate is 9.85%. Then ISIGHT was used to make the non-linear optimization on the structural parameter of L-shaped bionic groove. The maximum drag reduction rate of bionic blade was confirmed as the objective function. The design variables and the constraint conditions were determined. The sample points and testing sample points were obtained by using Latin Hypercube. The Multi-Island Genetic Algoritnm was selected to optimize the blade. The drag reduction performance of optimized bionic blade increases greatly, and the maximum drag reduction rate is 11.498%, which is in a relatively high level in the bionic mechanical design field. The drag reduction is ideal.3. The preparation of bionic blade and the drag reduction experimentThe test on the drag reduction performance of bionic blade was made through the experiment method, and the simulation data was compared to verify the correctness of the bionic design. The L-shaped grooves were manufactured with carved CNC machine and l chemical method was used to make the mastoid hydrophobic surface. The test project of drag reduction performance was confirmed, the test table for drag reduction performance test of fluid machinery fixed component was set. Then the drag reduction performance of designed bionic blade was tested in this paper. Meanwhile, SEM method was used to scan and observe the hydrophobic surface of blade. Finally the validity of the drag reduction of bionic blade is verified.4. The drag reduction mechanism analysis of bionic bladeThe bionic structure can reduce the shear stress and the vortex on the wall of blade and energy loss in the blade flow field. The drag reduction effect area of the transverse groove were defined and analyzed. That tire vortexes are the important vortex structures to realize drag reduction was found. The drag reduction mechanism is: the fluid generates lots of vortexes when through the blade surface. The vortexes interact with grooves to generate secondary vortex, namely tire vortexes. The strengthening and development of tire vortexes weaken the momentum exchange process of turbulent boundary layer, and stabilize the flow field and reduce energy losses. The effect of drag reduction was further improved that the drag reduction rate reached at 13.2% by changing the h+、s+ of groove, which proved the validity of the analysis in this paper. The bionic rose mastoid structure of the blade pressure surface realized the increase of blade outlet flow, and has the hydrophobic effect. The hydrophobic surface has double micro structure by using SEM to scan and observe the hydrophobic surface of blade. The air in hydrophobic surface reduced the contact area between the fluid and the metal surface and the adhesion when the fluid flows through the surface of blade, which realized good drag reduction effect.