Modeling and simulation of flow pattern and curing during manufacturing of composite wind turbine blades using VARTM process
Vacuum-Assisted Resin Transfer Molding (VARTM) has become a widly used and rapidly growing manufacturing process for wind turbine blades. However, in the case of complex geometries, resin flow pattern during the VARTM process tends to be unpredictable. In addition, increasing the size and thickness of the blades is expected to result in additional technical difficulties. Therefore, use of flow pattern simulation tools has become a necessity in order to avoid costly and time-consuming trial-and-error procedures during manufacturing. In this thesis, a 3-D non-isothermal framework for modeling the VARTM process for a wind turbine blade was developed. The model was utilized in a case study optimizing inlet gate arrangement, resin temperature, and mold temperature to shorten the filling time. Sequential filling scheme was assumed and different inlet gate arrangements and activation times were used in the first phase of the study. It was observed that, although increasing the number of the inlet gates tends to shorten the filling process, its effectiveness kept decreasing monotonically. The generally observed filling issue was the formation of dry spots in the sandwich region at the bottom of the part. In the sandwich region, the core splits the flow and forms two flow fronts, one on the top and another at the bottom of the sandwich region. The two flow fronts converge right after the core. For some cases, the slow moving flow front beneath the core was not able to reach its way out and converge with the flow front on the top of the core. To overcome the problem, activation of the auxiliary inlet gates located on the top of the core was postponed. In the second phase of the study, different resin temperatures were used. Increasing the temperature up to 325°K resulted in shorter filling durations while increasing the temperature further produced dry spots beneath the core. From the flow pattern results in non-sandwich areas, it was concluded that resolving the issue of slow moving flow front at the bottom of the core vii makes it possible to decrease the filling time by 17% through increasing the resin temperature by 20°C. The effect of different mold temperatures on the filling time was examined in the third phase of the study. Increasing the mold temperature from the initial value (330°K) did not result in shorter filling times. To investigate the necessity of employing 3-D non-isothermal model, a 2.5-D non-isothermal model and a 3-D isothermal model were developed and their results were compared to the results of the 3-D non-isotheral model. The 2.5-D non-isothermal model was unable to accurately predict the flow behavior in the sandwich region. In addition, although the same inlet arrangement and activation times were used for all simulations, the predicted filling time using the 2.5-D model was 30% shorter than the filling time using the 3-D non-isothermal model. On the other hand, the predicted flow pattern for the 3-D isothermal model was very similar to that for 3-D non-isothermal model and the difference between the filling times was relatively small. However, since the model does not keep track of the temperature variations and curing during filling, the simulation of cure after the filling would not provide accurate results.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering.