Fig 1.
(A) Three temporal profiles at the nozzle exit investigated in this study; (B) schematic diagram of the test apparatus; and (C) the two nozzles used in this study (unit: mm). The large nozzle (D = 10 mm) was for the food dye experiments, and the size of the small nozzle (D = 4 mm) was chosen by using the similarity protocol for the particle experiments. xp is the streamwise penetration distance, and x0 is the virtual origin.
Table 1.
Summary of data on cough flow penetration distances.
tinject is the injection duration in the starting jet stage, tmax is the time when dx/dt < 0.01 m/s and the cough flow is considered to reach the maximum distance.
Fig 2.
Visualizations of the turbulent round starting and interrupted jets.
Case 1 [pulsation], Case 5 [sinusoidal] and Case 8 [real-cough]. Rec = 5200 and Q/AD = 100 for all cases. The flow transition from the starting to the interrupted jet stage occurred at Uct/D = 100 when the source supply is terminated.
Fig 3.
Streamwise penetration distance as a function of time in the complete process of Case 3 [Pulsation, Re = 12900, Q/AD = 150].
Fig 4.
Streamwise penetration distances of the jet tips as a function of time.
(A) starting-jet stage; (B) interrupted-jet stage.
Fig 5.
Streak pictures of particles in Case 4 [Pulsation, Re = 12900, Q/AD = 250].
The jet boundary is indicated by the red dashed line. The pictures overlap from t = 0 to (A) the time when the jet is interrupted (t = tinj), and (B) t = 10tinj.
Fig 6.
The instant dispersion pattern of large particles in the interrupted jet (t = 4.5tinj).
The leading vortex is illustrated by red arrows, and white arrows indicate the particle motion.
Fig 7.
Particle streak lines from a long starting jet (Rec = 12,900, Q/AD = 5,000).