Characteristics of combustor diffusers

Results of an experimental investigation of the influence of blade wakes on the performance of several combustor prediffusers are presented. Two curved and two straight wall diffusers of different length, area ratio, and turning angle were tested with a single-stage compressor sited at a number of positions relative to diffuser inlet. Only a small increase in loss was incurred when the wakes from the outlet guide vanes were allowed to decay within the prediffuser. Distance along the mean streamline was found to be the most significant parameter influencing the decay of the wakes. In outwardly curved diffusers, a distance of about four blade chord lengths was required for these effects to be minimized.

The influence of blade wakes on the performance of combustor shortened prediffusers

An experimental correlation is presented between the losses and the inlet flow conditions in short dump diffusers for turbojet combustors. Cascades of compressor blades upstream of the diffuser were used to make the flow field at inlet similar to that in a real jet engine. The flow field was altered in two ways — by varying the distance between the cascades and the diffuser inlet plane and by changing the blade aspect ratio. The measurements show clearly that distortions in the radial direction affect the losses to a much larger extent than non-uniformities in the circumferential direction. In consequence, the performance can be correlated to a satisfactory degree of accuracy simply by using the radial blockage factor at inlet.

The relation between losses and entry-flow conditions in short dump diffusers for combustors

This study experimentally determined the effects of dominant geometric and flow parameters on the aerodynamic performance of an annular combustor-diffuser system. For each parametric configuration, data were obtained at 13 different flow rates through the inner annulus, outer annulus, and combustor dome. The parametric effects investigated included the dump gap dimension, flow splits, prediffuser inlet velocity profile, and combustor channel height. During these measurements, the average prediffuser inlet Mach number was 0.305. The measured static pressure recovery coefficient and the total pressure loss coefficient in the prediffuser as well as the overall system are presented in this paper. The study found that the performance of the combustor-diffuser system improves with increasing dome flow rate or dump gap dimension.

P. Pucher

Papers

The Effect of Blade-Wakes on the Performance of Short Dump-Diffuser Type Combustor Inlets