Background-Flow Considerations (Cont'd) Boundary layer transition Laminar Laminar Transition- Turbulent boundary boundary boundary layer layer layer V Ren≤2x105 Ren≥2×105 Separation Separation 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? ReDV2×105×15.89×10-6 =14.4 m D 0.22 S But other factors also involved (surface roughness, wind,ball spin,etc.) #7 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        