The characterisation of liquid sprays injected from circular and non-circular nozzles into high speed subsonic cross-airstreams

Regan, Nicholas J (2012) The characterisation of liquid sprays injected from circular and non-circular nozzles into high speed subsonic cross-airstreams. Doctoral thesis (DPhil), University of Sussex.

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This study was motivated by a need to better understand the sprays that can develop when oil leaks occur in gas turbine engines. Current gas turbine engines incorporate an extensive network of oil distribution pipes which deliver lubrication oil to bearings and seals at various locations across the engine. Parts of the oil pipe network are situated in hot, high pressure engine cavities where an oil leak, from a fractured pipe or leaking seal, could ignite and lead to an engine fire.

Oil leaks in gas turbine engines create liquid injection in cross-airstream situations, a subject which has been widely studied for combustion systems. However, previous studies are almost exclusively based on circular nozzle geometries. For a fractured oil pipe, the geometry through which the oil leaks approximates to a slot shape rather than a circular nozzle.

Sprays which develop in cross-airstreams are most sensitive to the parameters of Weber number (Weg eq) and momentum flux ratio (q). A wide range for these parameters are considered to be possible in engine oil leak scenarios because of the variety of crack dimensions possible and range of airflow conditions across the different sections of the engine; from zero to in excess of We g eq = 4000 and q = 300 could be possible in extreme cases.

The aim of this study was to generate and then characterise sprays in representative conditions. The main focus was the characterisation of the droplets which formed in the sprays, with the key objective of providing validation data for CFD codes. Droplet characterisation was performed using a phase Doppler particle analysis system. High speed video as well as pulsed laser sheet digital imaging were also used in the study to provide insight into upstream features of the spray field.

A 0.5 x 5.38 mm slot shaped nozzle geometry was used in two orientations; perpendicular alignment ↓↓⦶ and parallel alignment ↓↓⦶ . Water was injected into a cross-airstream over a twelve point test matrix with momentum flux ratios (q) values within the range of 4 ≳ q ≳ 32 and Weber number (We g eq) values within the range of 300 ≳ We g eq ≳ 1600.

The position of the spray was highly dependent on slot nozzle orientation. The spray was considerably further offset from the nozzle injection wall in parallel alignment ↓↓⦶ , compared to the perpendicular alignment ↓↓⦶. However, the centre-line distribution of Arithmetic Mean Diameter (AMD) was similar for both orientations, albeit offset further from the injection wall for the parallel slot nozzle. The underlying structure of droplet size distribution was consistent with results for sprays from circular nozzles.

At low liquid injection pressures the sprays produced by the perpendicular aligned slot ↓↓⦶ exhibited impingement, producing large droplets in the near wall region. Where impingement was not present, the data showed that AMD was not significantly influenced by the orientation of the slot nozzle; with all tests generating results in the range of 16 μm ≳ AMD ≳ 80 μm.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Engineering and Informatics > Engineering and Design
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA0349 Mechanics of engineering. Applied mechanics > TA0357 Applied fluid mechanics
T Technology > TJ Mechanical engineering and machinery > TJ0751 Miscellaneous motors and engines Including gas, gasoline, diesel engines
Depositing User: Library Cataloguing
Date Deposited: 23 Apr 2012 11:19
Last Modified: 10 May 2017 09:30

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