GAMMA VE BC GEÇİŞ MODELLERİNİN DIŞ AKIŞLAR İÇİN DEĞERLENDİRİLMESİ VE KARŞILAŞTIRILMASI

Abstract

Modelling of transition from the laminar to turbulent flow became a hot topic due to recent developments in renewable energy, UAV technologies and similar aerospace applications. The transition from laminar flow to turbulence is challenging to model in CFD analysis. The drag is overestimated if the transition is neglected in CFD solutions by assuming the flow is fully turbulent. This results in missing the fundamental characteristics of the flow and inaccurate predictions of the flow field. The most popular transition models are Menter's models applied to the SST turbulence model and the Baş-Çakmakçıoğlu (BC) transition model applied to the Spalart-Almaras model. We have focused on Menter's simpler but more popular γ model and Baş Çakmakçıoğlu models. The γ model relies on the local turbulence intensity, which makes applying the model challenging in external flows. This difficulty stems from the complex relationship between turbulence decay and transition onset. BC transition model utilizes the free stream turbulence intensity. Both models are verified using the Klebanoff and ERCOFTAC flat plate cases and several 2D external flow cases. Skin friction coefficient results are compared to experimental data. Results show that both models predict transition very similarly. BC model is computationally cheaper and easier to implement than the γ model. Also, γ model suffers from boundary conditions ambiguity.