The Effect of Thermal Cycling on Deposition in an Impingement/Effusion Cooling Geometry

Experiments were conducted in a high-pressure deposition facility to study the effect of engine cycling on the successive buildup of deposits as aircraft shut down and power up at different intervals. The test facility simulates the pressure and temperature environment of a combustor liner or turbine vane cooling circuit. The coolant flow temperature reaches 894K (1150 °F) and discharges into a 17atm (250 psi) cavity pressure at a nominal pressure ratio of 1.027. AFRL05 test dust with a 0–10μm size distribution is added to the coolant gas stream at a loading that ranged from 80–120mg/m3. The cooling circuit consists of a double-walled impingement cooling plate and effusion cooling plate with nominal hole sizes on the order of 0.5mm in diameter. To simulate the effects of cycling, the facility is brought up to the desired operating conditions where the first batch of dust is delivered (2–8g). The facility is then ramped down to ambient conditions. Following a “dwell” period of approximately 24 hours, another batch of dust is delivered once the facility is brought back up to the desired operating condition again. Test data were acquired for one, two, and four cycles with different dust mass delivered. Values such as discharge coefficient, pressure ratio, Reynolds Number, and temperature are used to evaluate the effects of dust deposition on the impingement/effusion plate setup. Dust capture efficiency and flow blockage time histories are reported. Capture efficiency is shown to be insensitive to cycling whereas flow blockage is negatively impacted by increased number of cycles for the same total mass delivered. The sloughing of deposit structures during the cool down of the cooling circuit is postulated to be responsible for the observed behavior. Implications for engine operation in dust-laden environments are summarized.