Advanced Turbomachinery Simulation using STAR -CCM+mdx2.plm. Advanced Turbomachinery Simulation using

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  • Advanced Turbomachinery Simulation using STAR-CCM+

    Chad Custer, PhD

    Technical Specialist

  • 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

  • Structured Grid

    1.0 million cells y+ 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

  • Key Benefits Efficiency optimization with Optimate+

    Performance Mapping

  • Key Benefits Turbomachinery specific post-processing

    Performance Mapping

    Blade-to-blade projection

  • Key Benefits Turbomachinery specific post-processing

    Performance Mapping

    Meridional projection

  • Key Benefits Turbomachinery specific post-processing

    Performance Mapping

    Circumferential Averaging

  • 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

  • HB solver converges to the unsteady solution

    Residuals

  • Wakes resolved across interfaces

    Mid-span Entropy

    -3o

  • Time domain and harmonic balance solutions correlate well

    Unsteady Rotor Blade Loading

  • Unsteady wake interaction captured

    Velocity Magnitude

  • Local Efficiency 3

    -3o

  • Local Efficiency 3

    +1o

  • Time Averaged Local Efficiency 3

    -3o +1o

  • Circ. Averaged Local Efficiency 3

    +1o -3o

  • 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