Compliments Theory - Turbomachinery Aerodynamics - Lecture Slides, Slides of Turbomachinery

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In this lecture...

• Computational Fluid Dynamics for

turbomachinery

• Introduction and overview

• Grid generation

• Boundary conditions

Computational Fluid Dynamics

• There are various levels of CFD analysis
  • Simple Euler (potential flow) solutions
  • 2-D/axisymmetric Navier-Stokes solution
  • 3-D Navier-Stokes solution
    • Reynolds Averaged Navier-Stokes (RANS) and Unsteady RANS (URANS)
    • Large Eddy Simulation (LES)
    • Direct Numerical Simulation (DNS)
• CFD analysis could also be
  • Steady or unsteady
  • Incompressible or compressible
  • Laminar or turbulent
  • Internal or external flow

Computational Fluid Dynamics

• CFD involves solving the fundamental

governing equations of fluid flow:

• Conservation of mass

• Conservation of momentum

• Conservation of energy

• Equation of state

• Species conservation (reacting

flows)

Computational Fluid Dynamics

• Turbomachinery: complex shear

flows

• Shear layers on rotating surfaces
• Shear layers developing on curved surfaces
• Separated flows: shock-boundary layer interaction, corner separation…
• Swirling flows and vortices
• Interacting boundary layers

Computational Fluid Dynamics

• Challenges in turbomachinery CFD

• Grid generation
  • Complex geometry
  • Rotating domain
• Flow is 3-D, highly unsteady, rotating, and turbulent - Capturing the losses and other viscous effects - Turbulence modelling
• Fluid-structure interactions

Computational Fluid Dynamics

• Types of simulations

• 3D

• True geometry required
• Simulate secondary flows, shock locations
• End wall boundary layers

• Transient or stationery

• Stationery simulations more common
• Transient: flow unsteadiness, vortex shedding, wake interaction with rotors

Computational Fluid Dynamics

• Solver

• Euler
• 3D NS
• RANS, URANS
• DES, DDES
• LES
• DNS

Grid Generation

Structured grid with multiple blocks

Blocks

Grid Generation

Unstructured grid

Grid Generation

• Topology

• Is a structure off blocks that acts as a framework for placing mesh elements.
• Blocks are laid out without gaps with shared edges and corners.
• Blocks contain same number of elements along each side.
• Is usually invariant from hub to tip.
• Can be edited on 2-D layers from hub to tip sections.
• Number of blocks will dictate the skewness of the grid elements.

Grid Generation

• Grid topology schemes

• O-grid:
  • Usually used around the blade by forming a continuous loop around it
  • Yields excellent boundary layer resolution
  • gives good control over the y + values that needs to be tightly monitored
  • Provides near orthogonal elements on the blades

Grid Generation

• J-grid:
  • Usually used near leading and trailing edges
  • Wraps up in opposite directions at the leading and trailing edges
• H-grid:
  • Tends to complete the meshing by adding some blocks in an unstructured manner
  • The structured blocks extend from upstream of the LE, downstream of the TE and between the blades and the periodic surfaces

Grid Generation

J-grid topology (^) H-grid topology