Electrostatic Effects on Airborne Particle Deposition in Gas Turbine Engines

Abstract Experiments were conducted to determine the effects of electrostatics on the deposition of airborne dust particles within a gas turbine hot section. One experiment simulates particle-laden flow through an impingement cooling jet. Dust (0–5 μm Arizona Road Dust) was entrained with hot air through a 3.66 m long, 6.35 mm diameter tube at a mean velocity of 57 m/s. The gas temperature ranged from 755 K to 1005 K to test temperature sensitivity of any electrostatics effect. As the dust travels through the pipe, it collides with the pipe’s walls and other dust particles resulting in tribocharging. The dust-laden jet impinges on a charged plate (−12 kV to +12 kV) where a deposit is formed. The effect of plate charge on the deposit formation was assessed pertaining to its size, shape, and volume. A second experiment was performed to determine the effect of electrostatics on deposition in a double-walled cooling circuit. A charge (−5 kV to +5 kV) was applied to both the effusion interior and impingement exterior enclosures. Dust (0–5 μm Arizona Road Dust) was entrained in an 810 K flow with a pressure ratio (PR) of 1.03 to simulate gas turbine cooling flow operating conditions. No significant electrostatic effect was observed for this geometry. These two results at relevant temperatures for gas turbine cooling were corroborated by additional gravity drop experiments at lower temperature: through charged parallel plates and through a charged cylindrical pipe. These more fundamental tests confirmed the finding that ARD particles tribocharge negatively and are thus attracted to positive potential surfaces. This effect appears to be augmented at higher temperature. Also, the cylindrical pipe gravity drop results confirmed that when particles are in an enclosed geometry, no electrostatic effect is observed due to the lack of electric field lines.