Jixian Yao

Unsteady Interaction Between a Transonic Turbine Stage and Downstream Components

Results from a numerical simulation of the unsteady flow through one quarter of the circumference of a transonic high-pressure turbine stage, transition duct, and low-pressure turbine first vane are presented and compared with experimental data. Analysis of the unsteady pressure field resulting from the simulation shows the effects of not only the rotor/stator interaction of the high-pressure turbine stage but also new details of the interaction between the blade and the downstream transition duct and low-pressure turbine vane. Blade trailing edge shocks propagate downstream, strike, and reflect off of the transition duct hub and/or downstream vane leading to high unsteady pressure on these downstreamcomponents. The reflection of these shocks from the downstream components back into the blade itself has also been found to increase the level of unsteady pressure fluctuations on the uncovered portion of the blade suction surface. In addition, the blade tip vortex has been found to have a moderately strong interaction with the downstream vane even with the considerable axial spacing between the two blade-rows. Fourier decomposition of the unsteady surface pressure of the blade and downstream low-pressure turbine vane shows the magnitude of the various frequencies contributing to the unsteady loads. Detailed comparisons between the computed unsteady surface pressure spectrum and the experimental data are shown along with a discussion of the various interaction mechanisms between the blade, transition duct, and downstream vane. These comparisons show-overall good agreement between the simulation and experimental data and identify areas where further improvements in modeling are needed.

Massively Parallel Simulation of the Unsteady Flow in an Axial Turbine Stage

The results from two numerical simulations of the unsteady flow in a 11 stage axial-flow turbine are presented and compared with experimental data to show both the effect of blade count on the solution accuracy and the time-averaged and unsteady flow physics present. TFLO, the three-dimensional, multiblock, massively parallel turbomachinery flow solution procedure is used to simulate the flow through the Aachen 36-vane/41-blade/36-vane 1 ½-stage turbine rig. Comparisons of the time-averaged and unsteady flow solutions of 1-vane/1-blade/1-vane and 6-vane/7-blade/6-vane configurations with the available experimental data are used to show the importance of matching actual blade counts in unsteady flow simulations as closely as possible. In addition, these comparisons are used to quantify the predicted aerodynamic performance differences and highlight the different unsteady flow physics in the two simulations.

Computational approach for predicting stall inception in multistage axial compressors

A new time-accurate computational approach for predicting stall inception due to long- and short-wavelength phenomena in multistage axial compressors is introduced. The computational approach uses a time-accurate single-blade-passage multi-blade-row strategy that includes many of the primary unsteady modes associated with the early symptoms of stall. High-frequency unsteadiness due to self-excited flow at scales of the blade passage and rotor tip clearance as well as low-frequency unsteadiness due to longitudinal system modes are included in this model. The new approach is demonstrated using the NASA Stage35 single-stage configuration with an extended up- and downstream duct. Nothing precludes the use of this model, however, for multistage and/or multipassage per blade-row configurations if the computer resources are available. The results from a series of time-accurate simulations near stall with this new approach are presented to demonstrate the self-excited unsteady pressure levels and frequencies that are computed to exist before, during, and just after stall. Results show that the self-excited flow has significant unsteady pressure amplitude and a spectrum containing both low-frequency system waves and high/moderate-frequency waves corresponding to the passage self-excited viscous flow in each blade row.

Unsteady flow investigations in an axial turbine using the massively parallel flow solver TFLO

The results from two numerical simulations of the unsteady flow in a 1-1/2 stage axial-flow turbine are presented and compared with experimental data to show both the effect of blade count on the solution accuracy and the time-averaged and unsteady flow physics present. The TFLO three-dimensional, multi-block, massively parallel turbomachinery flow solution procedure is used to simulate the flow through the Aachen 36-vane/41-blade/36-vane 1-1/2 stage turbine rig. Comparisons of the time-averaged and unsteady flow solutions of 1-vane/1-blade/1-vane and 6-vane/7-blade/6-vane configurations with the available experimental data are used to show the importance of matching actual blade counts in unsteady flow simulations as closely as possible. In addition, these comparisons are used to quantify the predicted aerodynamic performance differences and highlight the different unsteady flow physics in the two simulations.