CFD VALIDATION OF NASA STAGE 67 WITH A ROTOR WAKE MODELLING APPROACH AND AN UNEQUAL PERIODIC BOUNDARY TREATMENT

Abstract

The flow field of the NASA Stage 67 has been computed numerically using the ANSYS Fluent solver (2021). The upstream rotor and downstream stator domains of the compressor stage were computed separately. The rotor domain was validated firstly, and good consistency are shown between the numerical results of the rotor-only case and the experimental data. A comprehensive analysis and modelling of rotor wakes in the rotor-only case was then presented. The Gaussian distribution approximations are shown to approximate the rotor wake mean velocity profiles well within the middle and higher span surfaces and a 2D expression for the rotor the far-wake at these surfaces has been developed. The study also focused on the rotor-wake-stator interactions which was implemented through CFD simulations of three rotor-stator cases with the same rotor and stator blade counts (22 blade) and different rotor-stator gaps using a sliding mesh method. Certain positions where the stator influence on the rotor wake was found limited and can be ignored, and the downstream blade flow can be simulated separately from that upstream. The streamwise plane at about 0.38 stator blade chord upstream of the stator leading edge was chosen to split the stator-only case from the rotor-stator case. The stator-only case selected this plane as inlet where the rotor wake profiles were modelled using Gaussian distributions and taken as inlet boundary conditions, which, however, was concluded as the wake modelling approach. The wake modelling approach was also extended into the stator-only case with 34 blades, which was a non-integral rotor-stator blade counts case. A new method to account for unequal rotor and stator blade pitches is developed, based on using a short streamwise distance to relax the solution from one based on the periodicity of the rotor blade geometry to one based on the stator blade geometry periodicity. Both the time-resolved and time-averaged results of this case were shown good consistent with the experimental ones. Simulations have also been conducted with both a 2-pitch and 3-pitch wide domain to quantify the influence of the number of stator blades contained in the downstream domain. The differences between the results from the two domains was sufficiently small, and a 2-pitch wide domain is sufficient to yield reliable results. The rotor wake modelling approach studied in the thesis can provide a reliable and efficient method for use in the CFD simulation of multistage turbomachines. The method can simplify the simulation through splitting the domain in different rotational and stationary components.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Timothy Craft (Supervisor)