Advanced Turbomachinery Simulation using STAR-CCM+ Chad Custer, PhD Technical Specialist
Outline STAR-CCM+ is a robust tool well suited for many types of turbomachinery simulation Today’s talk will focus on just a few key objectives and capabilities Key Objectives – Conjugate heat transfer – Aeroelastic response – Performance mapping Key Capabilities – Complex geometry handling – Conformal polyhedral meshing – Pipelined workflow – Harmonic balance – Advanced post-processing
Conjugate Heat Transfer Key Capabilities Geometry handling – Direct CAD import – 3D CAD editing Meshing – Polyhedral cells – Conformal interfaces – Automatic prism layer generation
Cooled Turbine Blade Key Capabilities Geometry handling – Direct CAD import – 3D CAD editing Direct import of CAD solid geometry External and cooling air volumes generated using 3D CAD
Cooled Turbine Blade Key Capabilities Meshing – Automatic mesh generation • Pipelined meshing • Simple global size settings • Local refinement control • Automatic solution interpolation
Cooled Turbine Blade Fewer cells required Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells
Cooled Turbine Blade Key Capabilities Good for swirling flow Meshing such as tip vortices – Automatic mesh generation – Polyhedral cells Polyhedral cell faces are orthogonal to the flow regardless of flow direction
Cooled Turbine Blade High quality cells, even Key Capabilities with complex geometry Meshing – Automatic mesh generation – Polyhedral cells
Cooled Turbine Blade Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells – Conformal interfaces – Automatic prism layer generation Cells are one-to-one connected on the solid/fluid interface Fluid-side prism layers are automatically generated
CHT Validation: NASA C3X Cooled Vane The C3X is commonly used to validate heat transfer simulation Structured and unstructured (polyhedral) grids with and without transition modeling are analyzed Other work has been performed on the C3X using STAR-CCM+ by – Solar Turbines (GT2006-91109) – Honeywell (GT2012-68861)
Polyhedral Grid 1.0 million polyhedral cells Extruded cell topology in the span- wise direction y+ of less than one
Structured Grid 1.0 million cells y+ less than one
HTC sensitivity to Inlet Turbulent Viscosity Ratio Heat transfer coefficient is sensitive to inlet turbulent viscosity ratio TVR VR=1 =10 TVR VR=7 =70 TVR VR=4 =40 TVR=100 100
Structured Grid: HTC for γ -Re θ Transition model Solutions produced with STAR-CCM+ correlate more closely to experiment than reference simulations Hylton, L.D., Mihelc, M.S., Turner, E.R., Nealy, D.A., York, R.E., “Analytical and Experimental Evaluation of the hHeat Transfer Distribution over the Surfaces of Turbines Blades”, NASA CR 168015, May 1983
Comparison of Mesh Solutions Structured and polyhedral mesh solutions correlate well Polyhedr hedral al Struc uctur ured ed
Comparison of Heat Transfer Coefficient: No Transition Polyhedral mesh correlates more closely with experiment when transition is not considered Polyhedr hedral al Struc uctur ured ed Polyhedr hedral al Struc uctur ured ed
Comparison of Heat Transfer Coefficient: With Transition Polyhedral mesh and structured grid produce comparable results when transition is considered Polyhedr hedral al Struc uctur ured ed
C3X Conclusions STAR-CCM+ accurately predicts surface pressure and heat transfer Transition modeling is important in accurately modeling heat transfer Polyhedral mesh shown to correlate more closely with experiment than structured grid Polyhedral meshing technology allows conformal meshing of complex geometries
• Simulations are being performed on the GE Energy efficient engine • All Cooling holes and internal geometry is modeled GE Energy Efficient Engine
Aeroelastic Response Traditional simulation methods present many challenges Aeroelastic analysis must be run unsteady Traditional unsteady simulation is challenging – Very long run times – Must mesh the entire machine – Hard to specify blade vibration – Hard to extract stability information • Harmonic balance method in STAR-CCM+ resolves each of these challenges • The HB method is not available in any other commercial package
Harmonic Balance Basics The harmonic balance method takes advantage of the periodic nature of a turbomachine Solves a set of equations that converge to the periodic, unsteady solution Full non-linear solver All unsteady interactions captured
Harmonic Balance Key Benefits Rapid calculation of unsteady solution Unsteady simulation must be run for many time steps to converge HB simulation converges to the unsteady solution 10x faster Red: Time Domain Blue: Harmonic Balance
Harmonic Balance Key Benefits Single blade passage mesh All blades must be meshed for an unsteady simulation Only one blade passage must be meshed for a HB simulation, however the solution is calculated for all blades Time Domain Harmonic Balance
Harmonic Balance Key Benefits Specify blade vibration – The vibration of each blade is staggered. This is known as the “Interblade phase angle” – To determine stability a simulation must be run for each phase angle – Traditional unsteady solvers require manual set up of motion for each phase angle – HB solver takes the inter-blade phase angle as a simple parameter
Example: D2 Vane Flutter Small vane motion results in large unsteady response Unsteady Pressure (Pa)
Example: D2 Vane Flutter Simulation run for many inter-blade phase angles If the work done on the blade is negative for all inter-blade phase angles, the vane is dynamically stable
Performance Mapping Key Benefits Complex geometry handling Polyhedral cells Already discussed High quality mesh Prism layer generation Harmonic balance solver Grid sequencing initialization Efficiency optimization with Optimate+ Turbomachinery specific post-processing
Performance Mapping Key Benefits • Drastically reduce run time Grid sequencing initialization • Reduce need for ramping • Increased simulation robustness Time to initialization: 80 seconds Initialization Converged Solution
Performance Mapping Key Benefits Efficiency optimization with Optimate+
Performance Mapping Key Benefits Turbomachinery specific post-processing Blade-to-blade projection
Performance Mapping Key Benefits Turbomachinery specific post-processing Meridional projection
Performance Mapping Key Benefits Turbomachinery specific post-processing Circumferential Averaging
Example: Aachen Turbine Performance Analysis Aachen turbine is a 1.5 stage cold-flow turbine Simulations will be performed using the harmonic balance method implemented within STAR-CCM+ Analysis will be performed for two different vane clocking positions of +1 degree and -3 degrees - 3 o
Computational Domain Structured HOH mesh containing 1.85 million cells Near-wall cell thickness of 0.03 mm 8 cells resolve 0.4 mm tip gap
Residuals HB solver converges to the unsteady solution
Mid-span Entropy Wakes resolved across interfaces -3 o
Unsteady Rotor Blade Loading Time domain and harmonic balance solutions correlate well
Velocity Magnitude Unsteady wake interaction captured
3 Local Efficiency -3 o
3 Local Efficiency +1 o +1
3 Time Averaged Local Efficiency -3 o +1 o +1
3 Circ. Averaged Local Efficiency +1 o -3 o +1
Aachen Turbine Conclusions HB solver able to calculate the unsteady solution in 1/60 th the compute time as a time domain trial (GT2012-69690) Allows for clocking studies to be performed: – Efficiency of +1 degree clocking: 84.609% – Efficiency of -3 degree clocking: 84.663% Data can be visualized easily in the time domain or frequency domain
Overview STAR-CCM+ is a robust tool well suited for many types of turbomachinery simulation Today’s talk focused on just a few key objectives and capabilities Key Objectives – Conjugate heat transfer – Aeroelastic response – Performance mapping Key Capabilities – Complex geometry handling – Conformal polyhedral meshing – Pipelined workflow – Harmonic balance – Advanced post-processing
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