Measurements of fuel thickness for prefilming atomisers at elevated pressure

© 2020 Elsevier Ltd This work describes an experimental study of the fuel flows on the prefilmer of an aerospace gas turbine airblast atomiser at elevated pressure. The work identifies the physics leading to contradictory findings within the literature. This concerns an important atomisation boundary condition, whether the thickness of the fuel film on the prefilming surface influences the downstream drop size distribution. Analysis of the experimental data shows that fuel film thickness becomes uncorrelated with the downstream drop size if surface tension forces dominate inertia at the prefilmer tip. Fuel film thickness however provides the initial length scale for primary atomization if fuel inertia exceeds surface tension forces. It is the high inertial conditions that are associated with gas turbine operation, but the low inertial conditions that are readily achievable at laboratory scale through momentum flux scaling. Additionally, a detailed statistical description of the fuel flow has been provided for the atomiser tested. This reveals the importance of upstream hydrodynamic and aerodynamic boundary conditions on the probability of a ligament forming. Surprisingly, operating pressure is shown to have limited effect on the probability of ligament formation, a significant advantage for future modelling of the primary atomization processes

Integrated OGV design for an aggressive S-shaped compressor transition duct

Within gas turbines the ability to design shorter aggressive S-shaped ducts is advantageous from a performance and weight saving perspective. However, current design philosophies tend to treat the S-shaped duct as an isolated component, neglecting the potential advantages of integrating the design with the upstream or downstream components. In this paper such a design concept is numerically developed in which the upstream compressor outlet guide vanes are incorporated into the first bend of the S-shaped duct. Positioning the vane row within the first bend imparts a strong radial gradient to the pressure field within the vane passage. Tangential lean and axial sweep are employed such that the vane geometry is modified to exactly match the resulting inclined static pressure field. The integrated design is experimentally assessed and compared to a conventional non-integrated design on a fully annular low speed test facility incorporating a single stage axial compressor. Several traverse planes are used to gather five-hole probe data which allow the flow structure to be examined through the rotor, outlet guide vane and within the transition ducts. The two designs employ almost identical duct geometry, but integration of the vane row reduces the system length by 21%. Due to successful matching of the static pressure field, the upstream influence of the integrated vane row is minimal and the rotor performance is unchanged. Similarly the flow development within both S-shaped ducts is similar such that the circumferentially averaged profiles at duct exit are almost identical, and the operation of a downstream component would be unaffected. Overall system loss remains nominally unchanged despite the inclusion of lean and sweep and a reduction in system length. Finally, the numerical design predictions show good agreement with the experimental data thereby successfully validating the design process

An aggressive S-shaped compressor transition duct with swirling flow and aerodynamic lifting struts

In a multistage intermediate pressure compressor an efficiency benefit may be gained by reducing reaction in the rear stages, and allowing swirl to persist at the exit. This swirl must now be removed within the transition duct that is situated between the intermediate and high pressure compressor spools, in order to present the downstream compressor with suitable inlet conditions. This paper presents the numerical design and experimental validation of an initial concept which uses a lifting strut to remove tangential momentum from the flow within an S-shaped compressor transition duct. The design methodology uses an existing strut profile with the camber line modified to remove a specified amount of the inlet tangential momentum. A linear strut loading was employed in the meridional direction with a nominally constant loading in the radial direction. This approach was applied to an existing aggressive S-duct configuration in which approximately 12.5° of swirl remains at OGV exit. 3D CFD predictions were used for preliminary assessment of duct loading and to determine how much swirl could be removed. Consequently, a fully annular test facility incorporating a 1 1/2 stage axial compressor was used to experimentally evaluate four configurations; an unstrutted duct, a non-lifting strut and lifting struts designed to remove 50% and 75% of the inlet tangential momentum. Despite the expected large increase in loss caused by the introduction of struts there was not a significant additional loss measured with the inclusion of turning. No evidence of flow separation was observed and the data suggested that it may be possible to remove more swirl than was attempted. Although the turning struts did not remove the entire targeted swirl due to viscous deviation the data still confirm the feasibility of using a lifting strut/duct concept which has the potential to off-load the rear stages of the upstream compressor