advanced turbomachinery simulation using star...
TRANSCRIPT
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
Outline
Key Capabilities Geometry handling – Direct CAD import – 3D CAD editing
Meshing – Polyhedral cells – Conformal interfaces – Automatic prism layer generation
Conjugate Heat Transfer
Key Capabilities Geometry handling – Direct CAD import – 3D CAD editing
Cooled Turbine Blade
External and cooling air volumes generated
using 3D CAD
Direct import of CAD solid geometry
Key Capabilities Meshing – Automatic mesh generation
Cooled Turbine Blade
• Pipelined meshing • Simple global size settings • Local refinement control • Automatic solution interpolation
Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells
Cooled Turbine Blade
Fewer cells required
Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells
Cooled Turbine Blade
Good for swirling flow such as tip vortices
Polyhedral cell faces are orthogonal to the flow regardless of flow direction
Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells
Cooled Turbine Blade
High quality cells, even with complex geometry
Key Capabilities Meshing – Automatic mesh generation – Polyhedral cells – Conformal interfaces – Automatic prism layer generation
Cooled Turbine Blade
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
Heat transfer coefficient is sensitive to inlet turbulent viscosity ratio
HTC sensitivity to Inlet Turbulent Viscosity Ratio
TVR=10
TVR=40 TVR=100
TVR=70
Solutions produced with STAR-CCM+ correlate more closely to experiment than reference simulations
Structured Grid: HTC for γ-Reθ Transition model
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
Structured and polyhedral mesh solutions correlate well
Comparison of Mesh Solutions
Polyhedral Structured
Comparison of Heat Transfer Coefficient: No Transition
Polyhedral mesh correlates more closely with experiment when transition is not considered
Polyhedral Structured
Polyhedral Structured
Polyhedral mesh and structured grid produce comparable results when transition is considered
Comparison of Heat Transfer Coefficient: With Transition
Polyhedral Structured
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
C3X Conclusions
GE Energy Efficient Engine
• Simulations are being performed on the GE Energy efficient engine
• All Cooling holes and internal geometry is modeled
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
Aeroelastic Response
• Harmonic balance method in STAR-CCM+ resolves each of these challenges
• The HB method is not available in any other commercial package
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 Basics
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
Harmonic Balance Key Benefits
Red: Time Domain Blue: Harmonic Balance
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
Harmonic Balance Key Benefits
Time Domain Harmonic Balance
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
Harmonic Balance Key Benefits
Small vane motion results in large unsteady response
Example: D2 Vane Flutter
Unsteady Pressure (Pa)
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
Example: D2 Vane Flutter
Key Benefits Complex geometry handling Polyhedral cells High quality mesh Prism layer generation Harmonic balance solver Grid sequencing initialization Efficiency optimization with Optimate+ Turbomachinery specific post-processing
Performance Mapping
Already discussed
Key Benefits Grid sequencing initialization
Performance Mapping
• Drastically reduce run time • Reduce need for ramping • Increased simulation
robustness
Initialization Converged Solution
Time to initialization: 80 seconds
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
Example: Aachen Turbine Performance Analysis
-3o
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
Aachen Turbine Conclusions
HB solver able to calculate the unsteady solution in 1/60th 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
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
Overview