Session: 31-07 Compressor Off-Design Impacts & Stall Inception

Paper Number: 121637

121637 - Unsteady Flow Mechanism of Non-Synchronized Disturbance During Gas Turbine Compressor Start-Up 

In this paper, unstable unsteady flow phenomenon that occurs during startup in the compressor of a gas turbine for power generation are investigated in detail. After the rotating stall disappears during startup, a large-scale recirculating flow occurs at the tip of the 1st rotor over the entire circumferential direction. This stage mismatch causes a large flow separation on the casing wall and thus, increases the gas temperature of the tip.　This phenomenon ends as the rotational speed increases, and the condition stabilizes at the rated rotational speed, so basically it cannot be a problem. However, under certain IGV-VV schedule conditions, even at the rated speed, Non-Synchronized Disturbance (NSD) flow will be occurred. Based on these cases, the differences in aerodynamic unsteady flow mechanisms between large-scale recirculating flow and NSD flow were investigated using full annulus unsteady numerical simulations. 
In the case of the large-scale recirculating flow with a deeply closed IGV at 70% part speed, the large recirculating flow occurs in the range over 75% span from hub (%Ht) to the tip from the leading edge to about 80% axial chord upstream. 
On the other hand, if the IGV is slightly closed than the design opening at 100% speed, the reverse flow region occurs locally on the tip side near the leading edge of 95%Ht or higher in the 1st rotor tip. It was found that the rotation of the local reverse flow region in the circumferential direction causes NSD with a peak around 40%-60% of the 1st BPF. This was found to be an NSD caused by Kelvin-Helmholtz instability, which occurs when the shear layer between the tip leakage flow and the main flow oscillates.
The mechanism of the unsteady and unstable flow phenomenon which occurred at the start of the gas turbine compressor was clarified by the comparison analysis between the full annulus unsteady numerical simulation and the actual measurement. As a result, it is possible to clarify the direction of improvement measures and contribute to the gas turbine and turbomachinery communities.

Presenting Author: Ryosuke Seki Mitsubishi Heavy Industries, Ltd.

Presenting Author Biography: Ryosuke Seki received M.S. degrees in applied mechanics and aerospace engineering from Waseda University, Japan, in 2013. Since 2013, he has been a researcher at Turbomachinery No.2 Laboratory，Turbomachinery Research Department，Research & Innovation Center，Mitsubishi Heavy Industries (MHI), Japan．He engages in design of axial compressor for industrial gas turbine，development of CFD codes，application of CFD codes to some kind of turbomachines such as centrifugal compressor，turbochargers and steam turbine.
Since 2021,he is engaged in a wide range of turbomachinery business as a Deputy Manager and Professional Engineer, Japan. Obtained NAFEMS Professional Simulation Engineer (Advanced) in 2022. In 2023, he joined Whittle lab., University of Cambridge as an Industrial Fellow. Currently, he is leading and coordinating MHI's research and development of turbomachinery.

Authors:

Ryosuke Seki Mitsubishi Heavy Industries, Ltd.
Sho Bonkohara Mitsubishi Heavy Industries, Ltd.
Hidetaka Okui Mitsubishi Heavy Industries, Ltd.