Spray Transport Past Cylindrical Elements found in a Generic Aircraft Engine Nacelle
Figure 1: Clutter Array Spray Facility
Figure 2: PDA Optic Schematic
The characterization was performed upstream and downstream of a cylindrical tube array, which is of special interest in aircraft engine nacelle fire suppressant transport and distribution. Comparisons between these measurement techniques were conducted, the strengths and limitations of each technique were highlighted when applied to practical applications with large dynamic ranges.
Although the velocity determination of the two laser based systems were shown to be qualitatively consistent, Figure 5, with matching jet profile widths at half maximum velocity point, the PDA system recorded higher streamwise velocities compared to the PIV system. Regions of vortex shedding and high shear behind the clutter elements may also contribute to the discrepancy between the two measurement approaches.
Figure 5: Velocity Measured at 5.5 D Downstream of the Clutter
Furthermore, a histogram of drop sizes acquired downstream of the nozzle exit on the nozzle centerline, Figure 7, shows that the average drop diameter at this location was approximately 143 microns, and that the drop sizes typically ranged from 50 to 500 microns.
To address fire protection challenges which exist in aircraft engine nacelles, it is important to first understand the transport of high boiling point liquids as they are sprayed past clutter found in engine nacelles.
Unfortunately, there is a lack of reliable velocity/drop-size data downstream of generic clutter elements, Figure 1, found in nacelles.
ESI has undertaken a vigorous evaluation of two common optical methods,
Phase Doppler Anemometry (PDA)
Particle Image Velocimetry (PIV)
to ascertain their strengths and weaknesses. This was achieved by applying both methods to the transport of a suppressant.
Figure 3: PDA Measurement Volume Produced by the Intersection of Three Pairs of Laser Beams
Figure 4: PIV System Setup
The following data suggests that careful consideration must be taken when choosing an optical approach for the measurement of applications with large dynamic ranges, similar to those found in fire suppressant transport. As an example, drop size profiles were acquired 2D downstream of the spray nozzle as shown in Figure 6. The drop size is presented as both the arithmetic mean droplet diameter and the Sauter mean droplet diameter.
Figure 6: Mean and Sauter Diameter Profile Downstream of the Spray Nozzle
Figure 7: Droplet Size Histogram Acquire
Downstream of the Spray Nozzle