3.2.1. Basic Setup

Units

You can use either SI or Imperial units for the input data. Note that the standard unit systems are sometimes modified to reflect commonly used units in turbomachinery design. For example, rotational speed is specified in rpm and not in rad/s.

Configuration and Meshing

  • Rotational direction

    The direction of rotation of the blades about the Z axis. The choices are:

    • Right Handed

    • Left Handed (default)

  • Component Configuration

    The impeller blade arrangement. The choices are:

    • Main blade only

    • Main blade + 1 splitter (default)

    • Main blade + 2 splitters

  • Target mesh node count

    The desired number of mesh nodes per blade set. This number is used by the Turbo Mesh component to determine the mesh density when a Turbomachinery Fluid Flow system is generated.

  • Impeller tip configuration

    The choices are:

    • Unshrouded impeller

      The shroud is stationary (counter-rotating in the relative frame). Optionally select Include tip clearance to model nonzero tip clearance.

    • Shrouded impeller

      The shroud rotates with the blades. There is no tip clearance.

      Note:  The Turbo Setup system currently supports only centrifugal compressor blades with cut-off trailing edges. However, the trailing edge geometry makes no difference to the throughflow calculations, which remain valid for rounded trailing edges as well.

      While rounded trailing edges are not strictly supported for Turbomachinery Fluid Flow systems created by Turbo Setup, it is still possible to model them and take advantage of the Turbo Setup system as follows:

      1. Create the geometry with cut-off trailing edges and update the Turbo Mesh and Setup cells.

      2. Modify the geometry to use elliptical trailing edges and update the Turbo Mesh cell.

        Because the hub and shroud geometry are no longer split at the trailing edges, some boundary regions are eliminated and warnings are shown.

      3. Edit the Setup cell and (in CFX-Pre) correct the Hub and Shroud outlet boundary regions as indicated by the error messages.

        This normally involves editing the indicated boundary zones and then re-applying the entries in order to delete references to the eliminated boundary regions.

      4. Close CFX-Pre and run the calculations.

Inlet conditions

  • Pressure

    The stagnation pressure upstream of the impeller.

  • Temperature

    The stagnation temperature upstream of the impeller.

  • Meanline angle

    This setting controls the angle of the flow at the impeller leading edge, measured with respect to the axial direction (Z axis). The default of 0 degrees is for an approach flow without pre-rotation. A positive angle implies that the flow swirls in the machine rotational direction.

  • Radial distribution

    This setting controls the variation of the inlet gas angle in the radial direction (hub to shroud).

    The following options are available:

    • constant angle (default)

      Uniform inlet flow angle from hub to shroud defined by the meanline angle.

    • free vortex

      The inlet angle is determined by enforcing that be a constant value, where is the local inlet radius and is the local swirl velocity. The value of is itself determined from the meanline angle and meanline radius.

    • solid body rotation

      The inlet angle is determined by enforcing that be a constant value, where is the local inlet radius and is the local swirl velocity. The value of is itself determined from the meanline angle and meanline radius.

Material properties

  • Gas properties model

    Model option to set the equation of state used to calculate the specified gas properties.

    The choices are:

    • Ideal gas (default)

    • Real gas

      The Real gas option models the fluid as a real gas using the Aungier Redlich Kwong equation of state.

      Note that the gas properties applied here are valid only in the gaseous, superheat state. The CFX Setup component must be manually modified to perform calculations involving condensing fluids as detailed in Equation of State - Real Gas in the CFX-Pre User's Guide.

      It should also be noted that the default table generation settings are used with the Turbo Setup system. These settings may need manual adjustment in the CFX Setup component if the default temperature and pressure range prove to be too restrictive for the calculation. Details of the table generation settings can be found in Table Generation in the CFX-Pre User's Guide.

  • Material option

    Option to select either a predefined material from the database or define the required gas properties manually.

    The choices are:

    • Select material (default)

    • User specified

  • Material name

    Database material selection where Material option is set to Select material.

    The choices are:

    • Air (default)

    • Carbon Dioxide

    • Hydrogen

    • Methane

    • Nitrogen

    • Oxygen

    • Parahydrogen

    • Propylene

    • R123

    • R125

    • R134a

    • R141b

    • R142b

    • R245fa

    • Water

  • Dynamic viscosity

    Dynamic viscosity for the gas. This is treated as a constant value in the subsequent Throughflow and Turbomachinery Fluid Flow calculations. This is only available when Material option is set to User specified.

  • Gas constant

    The specific gas constant. This is available only when Material option is set to User specified.

  • Gamma

    The ratio of specific heats. This is available only when Material option is set to User specified and Gas properties model is set to Ideal gas.

  • Critical pressure

    The pressure at the vapor-liquid critical point of the gas. This is available only when Material option is set to User specified and Gas properties model is set to Real gas.

  • Critical temperature

    The temperature at the vapor-liquid critical point of the gas. This is available only when Material option is set to User specified and Gas properties model is set to Real gas.

  • Critical specific volume

    The specific volume at the vapor-liquid critical point of the gas. This is available only when Material option is set to User specified and Gas properties model is set to Real gas.

  • Acentric factor

    Conceptual state description parameter used alongside the above critical properties to determine the gas phase in the Aungier Redlich Kwong equation of state. This is available only when Material option is set to User specified and Gas properties model is set to Real gas.

  • Cp polynomial = fn(T(K))

    The Cp polynomial is used to calculate the specific heat capacity of the gas as a polynomial function of temperature. In this expression the units of temperature are always Kelvin regardless of the temperature units specified elsewhere. This is available only when Material option is set to User specified and Gas properties model is set to Real gas.

    • Minimum temperature

      The lower temperature limit of the valid range for the polynomial function.

    • Maximum temperature

      The upper temperature limit of the valid range for the polynomial function.

    • Polynomial coefficients

      The coefficients to in the following expression for :