Small airways have laminar air flow because:
Small airway have low reynold number, large cross sectional area, large diameter and air flows at a very low velocity. Ref: Physiology of respiration By Michael P. Hlastala, Albe J. Berger, Page 52; Review of Medical Physiology by William ganong, 22nd edn/page 583
Reynold's number > 2000
Very small diameter
Extremely low velocity
Low cross sectional area