1994 Volume 29 Issue 10 Pages 709-718
In industrial nozzles typically used for high load combustoos, the exit velocities are sufficiently large for the flow to be turbulent at nozzle exit. The flow issues from an annular nozzle whereby a region of reverseflow forms in the wake part of the bluff-body. The reverse-flow is instrumental to flame stabilisation.
Considerable understanding of the role of bluff-bodies has been achieved by measurements of aerodynamic flow patterns. However, in order to get a more detailed understanding of the role of bluff-bodies in the combustion of high speed spray flows, it way be necessary to investigate the distribution of size, number density and velocity of spray particles in the regions surrounding the bluff-body.
In the present study, a cone-type of bluff-body was fixed in the jet 23 mm from the nozzle exit. The experimental fuel is fed through a nozzle whose inner diameter is 0. 5mm. The nozzle pressure drop was selected to be either 20kPa or 50kPa.
For this work a Phase Doppler Particle Analyzer (PDPA) and Laser Sheet Photography (LSP) system were used to analyze the apray. The PDPA, Model DSA 3000 from Aerometrics, was set up for 2 axis velocity measurements and fiber-optic transmitter and collecter units. Detailed profiles of spray droplets were measured based on the PDPA together with overall visualization of the spray flow from the photographs.
The following are noted summarily from the experimental results:
(1) The mean diameters (D32 and DA) lie within the limits of 10-50μ m and 4-40μm, respectively. The particle sizes become significantly smaller in the side surface regions and wake parts of the bluff-body. However, the number density is higher in those areas.
(2) The volume flux of particle flows increases slightly near the side surface regions of the bluff-body, but was significantly lower in the wake part.
(3) The velocity of particles was higher at the top part, and was lower along the side surface region of the bluff-body. The recirculating vortex system was established in the wake regions of the bluff-body.