Experimental Two-Phase Flow Analysis Inside a Laboratory Scale Jet-Engine Combustion Chamber Using PIV

Abstract

The characterization of the two-phase kerosene/air flow near the nozzle of an aero engine combustor is important in order to understand the combustion characteristics of the burner. Typically, Particle Image Velocimetry (PIV) or Laser Doppler Velocimetry (LDV) is used to measure velocities inside aero engine combustors. However, these measurement techniques rely on tracer particles to visualize the flow field and are usually only able to measure the velocity field of one phase at a time. In the case of PIV measurements both the flow tracers and the kerosene droplets scatter the laser light and thus, appear on the PIV recordings. Depending on droplet size and flow velocity, these kerosene droplets do not necessarily follow the airflow leading to errors in the derived velocity field. This work presents a method on how to separate kerosene droplets from flow tracers depending on their optical characteristics in the PIV recording. This phase separation enables the independent measurement of the flow fields of both the gaseous and liquid phase at the same time using a standard PIV setup. The method is demonstrated on a laboratory scale aero engine combustor operated at atmospheric conditions. The test rig features liquid kerosene combustion with realistic inlet temperatures and pressure drop as well as good access for optical measurement techniques. The phases are separated by filtering the images with noise reduction filters for suppressing the signal of the flow tracers, and edge detection filters to detect the kerosene droplets. The detected kerosene droplets are removed from the PIV pictures and the pictures are evaluated using standard PIV cross-correlation. Afterwards the liquid phase images are evaluated using Particle Tracking Velocimetry (PTV). This phase separation can lead to errors in the derived velocity fields because of incorrect and incomplete particle detection or due to errors in the cross correlation at the edges of detected particles. These errors in the phase separation are quantified by evaluating artificial two-phase flow PIV pictures with similar optical properties to the actual two-phase PIV pictures, and comparing the derived velocity fields to the results calculated using the original, unaltered pictures. The obtained results show, that in the setup under investigation, gaseous and liquid phase can have significantly different flow fields with kerosene droplets moving in the opposite direction of the recirculating airflow. The influence of essential parameters like seeding and spray density are discussed and at positions with a sufficient data rate, the instantaneous slip velocity between droplets and gaseous flow is calculated. Generally, the presented method appears to be suitable for studying combustion with liquid kerosene injection.