Numerical Simulation of a Cross Flow Marine Hydrokinetic Turbine
Taylor Hall
Alberto Aliseda
University of Washington Mechanical Engineering
Northwest National Marine Renewable Energy Center (NNMREC)
Introduction
• Tidal energy resource realized
• Renewable
• Clean
• Predictable
• Many similarities to wind energy
Source: windows2universe
Axial Flow Turbines Cross Flow Turbines
Turbine Classifications
Source: Antheaume - Hydraulic Darrieus turbines efficiency for free fluid flow conditions versus power farm conditions
Turbine Design Concepts
Source: Department of Energy
Cross Flow Turbine Advantages
• High energy density typically found in narrow constricted channels
• Packing critical to efficiency and economic feasibility
• Cross flow turbines can be stacked, optimally utilizing limited space
• Work in any direction of flow
Source: Zanette - A design methodology for cross flow water turbines
Helical Cross-Flow Turbine
• Micropower Generation Project as benchmark study
• 4 helical blades, each with 90 degree sweep: Gorlov turbine
• Initial CFD simulation: flow over single helical blade in static position
Experiment/Simulation Parameters
• ReC =𝑉∞𝐶
𝜈= 28,000
• Aspect Ratio =𝐻
𝐷= 1.4
• Blockage ratio= 2𝑅𝐻
𝐶ℎ𝑎𝑛𝑛𝑒𝑙 𝐴𝑟𝑒𝑎 = 0.12
• Solidity Ratio =NC
2π𝑅= 0.075
• Tip Speed Ratio =ωR
V∞= 0
• Fluent v12.0
• Reynolds-Average Navier- Stokes (RANS) equations
• SST-kω turbulence closure model
• Transient simulation: Δt=0.5 sec
Turbine and Channel Flow Numerical Modeling
Discretized Domain • Gambit 2.4.6 • Domain sized to represent
experiment flume • 185,000 Elements • Same mesh for all blade
positions
Discretized Domain
o Structured in most volumes o Wall Functions
• 30<y+<300
•𝐹𝑖𝑟𝑠𝑡 𝐿𝑒𝑛𝑔𝑡ℎ
𝐶ℎ𝑜𝑟𝑑 𝐿𝑒𝑛𝑔𝑡ℎ= 0.15
First Length
Source: Antheaume - Hydraulic Darrieus turbines efficiency for free fluid flow conditions versus power farm conditions
Static Torque for a Single Blade
𝐶𝑇 =𝑇
12 𝜌𝑉∞
2𝑆𝑟𝑒𝑓
Flow fields for angles of attack (α) α=5⁰ α=60⁰
α=205⁰ α=25⁰
Static Torque for a Single Blade
𝐶𝑇 =𝑇
12 𝜌𝑉∞
2𝑆𝑟𝑒𝑓
Modeling in Near Wall Region Wall Functions
• 30< y+ < 300
•𝐹𝑖𝑟𝑠𝑡 𝐿𝑒𝑛𝑔𝑡ℎ
𝐶ℎ𝑜𝑟𝑑 𝐿𝑒𝑛𝑔𝑡ℎ= 0.15
• Total Elements = 185,000
Near Wall Approach • y+ < 1
•𝐹𝑖𝑟𝑠𝑡 𝐿𝑒𝑛𝑔𝑡ℎ
𝐶ℎ𝑜𝑟𝑑 𝐿𝑒𝑛𝑔𝑡ℎ= 0.0001
• Total Elements = 4.0 million
Near Wall: 20x computation time, 20-25% reduction in error
Near Wall Simulations
𝐶𝑇 =𝑇
12 𝜌𝑉∞
2𝑆𝑟𝑒𝑓
Sliding Mesh Stationary Domain Rotating Domain:
Tip Speed Ratio=3.6
Summary • Research into helical cross flow hydrokinetic turbines
• Validation of numerical simulations with laboratory experiments
• Simulation scaled to match laboratory experiments
• Investigated start up torque characteristics
– Many simulations in good agreement with experiments
– Positions with discrepancies to be improved
• Working toward simulation of steady state operation for rotating turbine blade
