Higher Gas Turbine Operation Flexibility by Improved Diffuser Vanes of a Radial Compressor STAR EUROPEAN CONFERENCE 2011 23 March 2011 Amsterdam, The Netherlands Dipl.-Ing. Anis Haj Ayed GmbH, Aachen, Germany
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Background Motivation & Task Compressor Geometry Operation Range Improvement Full Model Verification Conclusion Content
Advanced gas turbine process: high efficiency, complex process: Experiments showed need for operation range extension. uses STAR-CCM+ to investigate and improve single components with respect to operation range. High pressure compressor improvement case is presented. Background
Complex gas turbine control due to large number of components Repeated gas turbine trips due to stall of HP compressor Limited operating range of HP compressor: Limited gas turbine operation and control range Limited experimental flexibility Limited components life time due to increased vibrations levels and gas turbine trips (sudden shut down) Enlarge compressor operation range as much as possible by modifying as less parts as possible!! Motivation & Task
compressor inlet outlet scroll impeller inlet case vaned diffusor Compressor Geometry: Overview
outlet scroll impeller 17 vanes vaned diffusor 20 blades Compressor Geometry: Diffusor
Simplified segment model (rotational periodicity) One blade passage and one vane passage Simplified inlet case to include the bend in front of the impeller Coarse Calculation Grid - Fast calculation of full speed lines for different Vane configurations: operation range - Comparative evaluation of different vane designs Modeling Strategy
Turbulence Model: Realizable k,ε two layer, all y+ wall treatment Upstream Boundary: stagnation inlet Downstream Boundary: pressure outlet Interface type: Mixing plane diffusor outlet diffusor vane air inlet impeller blade coarse calculation grid (approx. 30000 cells) cyclic boundaries Calculation Model
surge at m = 4.38 kg/s surge point choke at m = 5.41 kg/s Calculation Result: original vane
velocity [m/s] original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Calculation Result: original vane
Mach Number [-] original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Calculation Result: original vane
Mach Number [-] modified vane original vane acceleration negative incidence mixing plane m = 4.39 kg/s (near surge) compressor blade Vane Modification
velocity [m/s] modified vane improved incidence mixing plane m = 4.39 kg/s compressor blade Calculation Result: Modified vane
Mach Number [-] modified vane improved incidence mixing plane m = 4.39 kg/s compressor blade Calculation Result: Modified vane
m = 0.4 kg/s (~ 9%) m = 0.22 kg/s (~ 4%) Calculation Results: Speed Lines
Full 360 degree Model including detailed inlet case, impeller, vaned diffuser and outlet scroll Unsteady simulation for: - original compressor - modified compressor Verification of Design performance Full Model Verification
Inlet pipe Unsteady calculation of original compressor Unsteady calculation of modified compressor impeller mass flow = 4.2 kg/s Turbulence Model: Realizable k,ε two layer, all y+ wall treatment Upstream Boundary: mass flow inlet Downstream Boundary: pressure outlet Outlet scroll Implicit unsteady solver, time step approx. 1.900.000 polyhedral cells Modeling Strategy
original compressor: reversed flow velocity [m/s] impeller Outlet scroll Calculation Results
modified compressor original compressor homogenous flow reversed flow impeller Outlet scroll velocity [m/s] Calculation Results
Modification implemented within two days at very low cost Surge/stall margin even larger than predicted - More stability during gas turbine start up - More operation flexibility of the complex gas turbine process - Possibility to identify behaviour of other components STAR-CCM+ as reliable and efficient Tool for Engineering Success Experimental Validation & Conclusion