1 Copyright Rolls-Royce Energy Systems, Inc. 2014

Proceedings of 2014 ASME Turbo Expo Turbo Expo 2014

June 16-20, 2014, Dusseldorf, Germany

GT2014-26989

UNSTEADY AERODYNAMICS AND FORCED RESPONSE STUDIES ON AERODERIVATIVE GAS TURBINE EXHAUST SYSTEM

ABSTRACT

Industrial and aeroderivative gas turbines use exhaust systems

for flow diffusion and pressure recovery. These processes result

in a three-dimensional, unsteady, turbulent, and complex flow

in the exhaust diffusers. The downstream balance-of-plant

systems such as heat recovery steam generators or selective

catalytic systems require, in general, a steady, uniform flow out

of the exhaust system.

Aeroderivative gas turbines for power generation application

have a wide operational envelope. Even though the exhaust

systems are designed for 70% load to 110% load, its

performance is significantly altered at low power operations.

Application of gas turbines at low power can increase exhaust

diffuser vibrations because of diffuser flow separations and

wakes from the last stage of the power turbine. Aerodynamic

excitations which result in excessive structural vibration can

cause the units to trip and the power plant to stop, resulting in

customer revenue loss.

The primary motivation for this research is to investigate an

aerodynamic mechanism to ensure reliable operation of the

exhaust system by identifying the regimes where aerodynamic

instabilities can occur. In-house and university supported

initiative to predict unsteady aerodynamics at low power

conditions shows the presence of turbulent and time dependent

flow.

The frequency spectrum results are discussed for low power

and high power gas turbine operating conditions. The numerical

predictions are in good agreement with test results.

NOMENCLATURE

TDC exhaust diffuser top dead center

U primary dependent variable vector

Fi flux vector

Gi stress vector

Pr Prandtl number

R body force vector

Re Reynolds number

S surface area

T temperature

E total internal energy

k turbulent kinetic energy

p pressure

s complex frequency

t time

ui velocity vector

xi spatial vector

y+ non-dimensional distance from wall

reference domain

ij kronecker delta

turbulent kinetic energy dissipation rate

ratio of specific heat

wave number

bulk viscosity

viscosity of air

t turbulent viscosity

ij viscous stress tensor

density of air

turbulent kinetic energy specific dissipation rate

Luca Di Mare Lecturer Whole Engine Modeling

Imperial College London London, UK

Deepak Thirumurthy Aerothermal Specialist

Rolls-Royce Energy Systems, Inc. Mount Vernon, Ohio, USA

Jeffrey S. Green Associate Fellow Vibrations

Rolls-Royce plc. Moore Lane, Derby, UK

John Myers Lead Experimental and Design Systems

Rolls-Royce Energy Systems, Inc. Mount Vernon, Ohio, USA