Background- Flow Considerations(Contd) Boundary layer transition Laminar Laminar ransition Turbulent bound boundary boundary laver a layer → Rep≤2×10 Rep22×10 Separation Separation Momentum of fluid in a turbulent boundary layer is greater, and thus separation occur further along the object Example How fast must a soccer ball travel to expect a turbulent boundary layer? D 2×103×1589×10 144 D 0.22 But other factors also involved (surface roughness, wind, ball spin, etc.) Heat Transfer Su Yongkang School of Mechanical EngineeringHeat Transfer Su Yongkang School of Mechanical Engineering # 7 Background – Flow Considerations (Cont’d) • Boundary layer transition • Momentum of fluid in a turbulent boundary layer is greater, and thus separation occurs further along the object. Example How fast must a soccer ball travel to expect a turbulent boundary layer? But other factors also involved (surface roughness, wind, ball spin, etc.) s m D V D 14.4 0.22 Re 2 10 15.89 10 5 6 =    = = − 