Ismail, Mohd Azmi bin (2014) Enhancement of heat transfer performance on nacelle lip-skin for swirl anti-icing. (PhD thesis), Kingston University, .
Abstract
Ice accretion on the wing and nacelle leading edges diminishes aerodynamic performance and increases fuel consumption and chances of aircraft crash. For these reasons, the Federal Aviation Administration mandates aircraft manufacturers to demonstrate that their aircraft can fly safely in icing conditions. This study has investigated the thermal performance and measures for improvement of Swirl Anti‐Icing (SAI) systems in preventing ice accretion on nacelle leading edges. A Piccolo Tube Anti‐Icing (PTAI) system with experimental data was used as the benchmark of this study. PTAI consists of perforated pipe and is installed inside the wing and/or nacelle leading edge. The hot air from the compressor is directed onto inner skin through the holes/nozzles in a perforated pipe. As a result, the inner skin is warmed up and free from icing. In this study, numerical simulations have been performed to analyse the thermal performance of PTAI at 4 different altitudes/scenarios namely Ground Run, Climb, Hold and Descent. The FLUENT CFD results demonstrated excellent agreements with the experimental data obtained by Bombardier Aerospace. Based on the results, the gradient coefficients of the empirical equations proposed by colleagues have been modified to take into account the ambient air temperature in order to make the correlations suitable for all the 4 conditions analysed. In future, Bias flow Acoustic Liner (BAL) is expected to be employed in engine nacelle and to form part of the inner skin of nacelle lip. The hotspots produced by PTAI would possibly destroy BAL. Thus, an old and mature technology, SAI, was further investigated in the present study with a hope to get rid of hotspot phenomenon on the inner skin and to increase the efficiency of the system. SAI has better temperature distribution along nacelle lip‐skin than that of PTAI. In addition, SAI contains fewer components, requires simple plumbing, and is light and inexpensive both for the system itself and for maintenance of the system compared to PTAI. Some potential modifications of nozzle including sloped nozzle, altered nozzle length and nozzle outlet, rotated nozzle towards inner skin, decreased exhaust area and increased nozzle diameter have been proposed and investigated in order to improve thermal performance of SAI. According to the results, only nozzle directions and nozzle diameters had significant effects on the thermal performance of SAI although all the modifications would have certain effects on anti icing performances of SAI. Thermal performance of SAI was inversely related to nozzle diameter. The hotspot temperature decreased by 18.53°C and cold spot temperature increased by 2.30°C respectively as the nozzle rotated 13° towards inner skin at hot air mass flow rate of 0.0118kg/s. For hot air mass flow rate of 0.04536 kg/s, the cold spot temperature decreased from 28.78 to 6.37°C as nozzle diameter increased from 0.0127m to 0.0254m. In addition, the temperature distribution on the nacelle lip‐skin has improved as the angle of nozzle direction towards inner skin increased. Based on the results, novel empirical correlations for SAI system have been developed and presented. The augmentor was employed in SAI system in order to enhance momentum and heat exchanges between hot air and cold air in the D‐chamber. As a result, the uniformity of temperature distribution and thermal performance of SAI on the nacelle lip‐skin were improved. The results showed that the thermal performance of SAI with augmentor increased with the increase of hot air mass flow rate. Although SAI with Augmentor 3 at 2° rotation showed poor thermal performance than SAI without augmentor but nozzle rotating at 13° with hot air mass flow rate above 0.028kg/s, the former showed better thermal performance than latter for hot air mass flow rate equal to or lower than 0.028kg/s. The performance of the Final nozzle was also tested and compared with the performances of Circle nozzle and ellipse nozzle 1. The final design of the nozzle has demonstrated the best performance at any given hot air mass flow rate, especially at 0.04356 kg/s. At this mass flow rate, Ctem deviation, hotspot temperature and cold spot temperature were 13.19%, 371.42K and 322.02K respectively. The hotspot temperature, temperature difference between hotspot and cold spot, standard temperature deviation and coefficient of temperature deviation produced by SAI were lower, while anti‐icing efficiency and cold‐spot temperature of SAI were higher than PTAI despite PTAI having higher average inner skin temperature than SAI. In other words, SAI showed better uniform temperature distribution on the nacelle lip‐skin compared to PTAI.
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