CFD Analysis of NREL Phase VI wind turbine

In this course, you will learn to conduct CFD analysis of NREL Phase VI wind turbine. You will learn every thing from scratch and using only basic data (NREL phase VI report, document number 29955.pdf) available on NREL website such as airfoil coordinates, twist angle and chord length along radial stations and torque values for different wind speeds. In this course you will use solidworks to create CAD model of NREL phase VI wind turbine, ANSYS Spaceclaim to create inner and outer domains, ICEMCFD for hybrid mesh for both domain and Fluent for solution and post processing. And finally you will compare present CFD results with experimental data provided by NREL.

This is the horizontal axis wind turbine (HAWT) whose data is released by national renewable energy laboratory (NREL) and used extensively for CFD validation studies on wind turbines by researchers.

In this course we are going to use the H-configuration of NREL phase VI wind turbine which has 3 deg tip pitch angle (also known as global pitch angle). We have used H-configuration because it is the most commonly used case by many researchers in CFD community in general and wind turbine community in particular. Therefore you can find plenty of CFD analysis data in research papers on this configuration which makes this course even more useful to large audience. 

From using basic data available in report (mentioned above), you will follow following steps:

1. CAD modeling in Solidworks (SW) by following following steps:

   • Downloading s809 airfoil coordinates from website or using provided files in dat/txt or excel format (full procedure is given).

   • Opening SW and making settings so that we can read airfoil coordinates in three dimensions (scan to 3D).

   • Setting the preferred units for the wind turbine model. 

   • Importing s809 airfoil coordinates into SW and creating base profile from these coordinates (3D sketch). And this base profile will be drawn on base plan at zero radial location. You will also create blunt trailing edge which will make it easier to make the high quality mesh and moreover in actual NREL phase VI wind turbine blade, the trailing edge is blunt/square.

   • We will then create 21 planes for the wind turbine blade (from 25% span to 100% span) as per given design data sheet in NREL report no. 29955 and project base profile on these 21 planes.

   • After that provide the required twist angle and chord length to these 21 profiles again as per design specifications given in NREL report.

   • Use loft command to create the blade solid from these 21 profiles. Please note that 25%-100% (75% span) is covered by S809 airfoil as mentioned in report and we have also done exactly same.

   • Now create two more lofts as per given data.

   • Save this model it in SW model and we will import it into spaceclaim for further processing.

     
     

2. Creating inner and outer domain in Spaceclaim (SC)

   • Import NREL phase VI wind turbine cad model in SW format into SC

   • Set origin of base of wind turbine at 0,0, 0.508, while 0.508 is the radial coordinate of wind turbine blade.

   • Provide global pitch angle (blade tip angle) of 3 degrees to wind turbine blade. 

   • Use move command with pattern option to create two blades from one blade.

   • Create sketch for hub and use pull command to make 3D solid body for the hub with little higher raduis than the 0.508 m (the end point of wind turbine blade with support)

   • Join two blades and hub to form single solid body of wind turbine model using combine option.

   • Create inner domain and subtract wind turbine solid from it so that can only fluid zone where flow can flow over the wind turbine outer surfaces.

   • Also create outer domain with given dimensions as shown in course videos and subtract inner domain from it.

   • As an optional exercise we will make half periodic model (180 deg) which can give you same results as full 360 model and requires half computational resources. But we will not continue with this model and we will use full 360 deg model in coming sections.

     
     

3. Creating tetra prism mesh for inner domain in ICEMCFD

   • Importing inner domain SC file (scdoc) into fluent

   • Setting up topo tolerance and tri tolerance for model. And run build topology.

   • Set sizes on different surfaces as per requirements

   • Set global mesh size

   • Create mesh using Octree algorithm and delete volume mesh. Smooth surfaces mesh up to required quality.

   • Create density box for mesh refinement in wake region behind wind turbine blades.

   • Create volume mesh using Delaunay algorithm.

   • Set prism mesh parameters and choose wind turbine from parts list for creation of prism layers on it.

   • Compute prism mesh with 5-7 layers initially and then crate more layers from Edit mesh menu by splitting each layer into 3 and thereby making 15-21 prism layers for boundary layer capturing.

   • Redistribute prism mesh so that we can get prism mesh in proper order.

   • Smooth volume mesh with prism elements, but this time with much care.

   • Check mesh quality and improve if it is low or negative.

   • Select Fluent as solver and set proper boundary conditions.

   • Export mesh into Fluent format (.msh)

     
     

4. Creating tetra mesh for outer domain in ICEMCFD

   • Import outer domain spaceclaim file into ICEMCFD

   • Set topo and tri tolerance and run build topology.

   • Set surface sizes on different parts

   • Create volume mesh using Octree algorithm

   • Delete volume mesh and keep surface mesh

   • Smooth surface upto required quality or maximum quality ICEMCFD can give you

   • Create density box for wake region capturing

   • Create volume mesh using Delaunay method

   • Smooth surface and volume mesh

   • Check mesh quality and if needed improve mesh quality.

   • Set solver as Fluent, provide appropriate boundary types and export mesh in Fluent (.msh) format.

     
     

5. Problem setup and solution in Fluent. And also compare CFD with experimental data.

   • Start Fluent with single core

   • Import both meshes i.e. inner and outer domain into Fluent using Read Mesh and Append command.

   • Make four partitions manually and save file case file with both meshes. Close Fluent

   • Open new Fluent session with four cores and read saved case file into Fluent with four core.

   • Set turbulence model, cell zone condition with given rpm of 72 using frame motion and boundary conditions such inlet velocity of 7 m/s and 10 m/s.

   • Set solver with coupled option and use settings shown in video carefully.

   • Autosave data file after every 50 iterations

   • Set solution monitors for torque (file, plot and consol)

   • Initialize solution and run solver. Follow video for more details.

   • Post process results

   • Compare torque, power and Cp from CFD with experimental data from NREL

You will also get one pdf file for the explanation of renewable energy and wind turbine energy. Go through it so that you can understand different concepts and formulas used in this course.