Abstract
The automobile sunroof buffeting problem must be avoided in the design of a sunroof system. Insufficient considerations of various design parameters have always resulted in many wind noise problems from prototypes to factory products. In this paper, a process of DOE (design of experiments)-based buffeting simulation at the engineering design stage is presented for the optimal design of an automobile sunroof system. The core methodologies of this process are PowerFLOW which can handle the important effects in the flow simulation and DFSS (design for six sigma) which can find out the optimal solution. Firstly, four main design parameters - angle of deflector, gap between roof and deflector, protrusion of deflector and glass opening length - are chosen as the control parameters of a DOE matrix from the 2D/3D parametric studies and possible levels are determined. After body leakage is adopted as the noise parameter, buffeting levels of nine cases are determined by direct CAE simulations. The analysis of these results leads to an optimal design solution and this is verified from additional simulations and comparisons with real-car experiments.
Through the comparisons with experiments, it is revealed that this approach can effectively capture the vortex shedding at a deflector and the acoustic feedback mechanism. The virtual buffeting test in the initial stage of sunroof and deflector layout design will enable an enormous cost reduction.
The results of this study are summarized as follows:
(1) The sunroof buffeting prediction using CAA is essential for selection of the position of the sunroof and the lay-out design of the sunroof deflector. Relevant virtual test and engineering design process was developed in the present study.
(2) This process can be used in the initial stage of deflector layout design, resulting in the enormous savings of man-hour and cost for problem-solving at later stages.
(3) The order of importance of contributions of the chosen control parameters are: opening length of sunroof glass > deflector protrusion ≒ deflector gap > deflector angle. The buffeting decreases as the opening length of sunroof glass and the deflector angle decreases, respectively, and as the deflector protrusion and the deflector gap increases, respectively.
Keywords: sunroof buffeting, simulation, sunroof design, DFSS, PowerFLOW