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cyclic Boundary Condition

NOTE: cyclic boundary condition is supported by boundary type cyclic, defined in the mesh file boundary. The difference between cyclic and cyclicAMI is the cyclic connects two equal meshes. Boundary condition cyclic requires the same size, same topology, same elements and even the same indexing order of faces!


        type            cyclic;
        inGroups        1(cyclic);
        matchTolerance  0.1;
        transform       rotational;
        neighbourPatch  rotor_periodic_2;
        rotationAxis    (0 0 1);
        rotationCentre  (0 0 0);
        nFaces          1628;
        startFace       171370;

Parameter rotationAxis defines the axis in Cartesian coordinates (directional vector of the axis).

Parameter rotationCentre is any point from the axis. So, the axis is defined by its directional vector and one of its points.
cyclic boundary condition is the same for all quantities (scalars, vectors, tensors):

p, U, k, omega, epsilon, T:

          type         cyclic;

Fan Efficiency

  • Pt    aerodynamic power, $ \color{white} P_\mathrm{t} = Y_\mathrm{t} \cdot \dot{m}_2 $ [W]
  • Pw    torque power, $ \color{white} P_\mathrm{w} = M_\mathrm{d} \cdot \omega $ [W]
  • f     compress factor, $ \color{white} f = 1- 0.36 \cdot \frac{\Delta p_\mathrm{s}}{p_\mathrm{s1}}$ [-]
  • Yst     static work, $ \color{white} Y_\mathrm{st} = f \cdot \frac{\Delta p_\mathrm{s}}{\rho^1}$ [m $ \color{white} ^2$/s $ \color{white} ^2$]
  • Yd    dynamic work, $ \color{white} Y_\mathrm{d} = \frac{c_2^2-c_1^2}{2}$ [m $ \color{white} ^2$/s $ \color{white} ^2$]
  • Yt    total work, $ \color{white} Y_\mathrm{t} = Y_\mathrm{st} + Y_\mathrm{d}$ [m $ \color{white} ^2$/s $ \color{white} ^2$]
  • psi    pressure number, $ \color{white} \psi = \frac{2 \cdot D \cdot \Delta p_\mathrm{t}}{\rho_1 \cdot c_c^2} = \frac{729.5 \cdot \Delta p_\mathrm{t}}{n^2 \cdot D^2 \cdot \rho_1}$ [-]
  • phi    flow number, $ \color{white} \phi = \frac{Q_w}{A \cdot c_c} = \frac{24.3 \cdot Q_w}{n \cdot D^3}$ [-]
  • axialForce    axial force on rotor, $ \color{white} F_\mathrm{a}$ [N]
  • pTotInlet     total pressure at the inlet, $ \color{white} p_\mathrm{t1}$ [Pa]
  • pTotVolute     total pressure at the outlet, $ \color{white} p_\mathrm{t2}'$ [Pa]
  • pTotOutlet     total pressure at the wheel outlet, $ \color{white} p_\mathrm{t2}$ [Pa]
  • pInlet     static pressure at the inlet, $ \color{white} p_\mathrm{s1}$ [Pa]
  • pVolute     static pressure at the outlet, $ \color{white} p_\mathrm{s2}'$ [Pa]
  • pOutlet     static pressure at the wheel outlet, $ \color{white} p_\mathrm{s2}$ [Pa]
  • magUInlet     velocity at the inlet, $ \color{white} c_1$ [m/s]
  • magUVolute     velocity at the outlet, $ \color{white} c_2'$ [m/s]
  • magUOutlet     velocity at the wheel outlet, $ \color{white} c_2$ [m/s]
  • massFlowInlet     mass flow at the inlet, $ \color{white} \dot{m}_1$ [kg/s]
  • massFlowVolute     mass flow at the outlet, $ \color{white} \dot{m}_2'$ [kg/s]
  • massFlowOutlet     mass flow at the wheel outlet, $ \color{white} \dot{m}_2$ [kg/s]
  • rhoInlet     density at the inlet, $ \color{white} \rho_1$ [kg/m $ \color{white} ^3$]
  • rhoVolute         density at the outlet, $ \color{white} \rho_2'$ [kg/m $ \color{white} ^3$]
  • rhoOutlet     density at the wheel outlet, $ \color{white} \rho_2$ [kg/m $ \color{white} ^3$]
  • volumeFlowRateInlet     volumetric flow rate at the inlet, $ \color{white} Q_\mathrm{w1}$ [m $ \color{white} ^3$/s]
  • volumeFlowRateVolute     volumetric flow rate at the outlet, $ \color{white} Q_\mathrm{w2}'$ [m $ \color{white} ^3$/s]
  • volumeFlowRateOutlet     volumetric flow rate at the wheel outlet, $ \color{white} Q_\mathrm{w2}$ [m $ \color{white} ^3$/s]
  • moment     torque at wheel, $ \color{white} M_\mathrm{d}$ [N $ \color{white} \cdot$m]
  • totalPressureDifference     difference in total pressure inlet-outlet, $ \color{white} \Delta p_\mathrm{t}$ [Pa]
  • staticPressureDifference     difference in static pressure inlet-outlet, $ \color{white} \Delta p_\mathrm{s}$ [Pa]

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Keywords in .tcfd file

In this section, keywords used in .tcfd file to setup cavitation modeling are described. See example of setting for water at atmospheric pressure and 20°C:

referencePressure 101325
referenceTemperature 293.15
referenceDensity 998
cavitationRisk yes

Values are expected to be in Pa, K and kg/m56, respectively. For turning on Multiphase cavitation, following keywords are necessary:

referencePressure 101325
referenceDensity 996


multiphaseCavitation SchnerrSauer

Multiphase cavitation modeling with Schnerr-Sauer model also has following optional parameters:

multiphaseCavitation-pSat 2300
multiphaseCavitation-sigma 0.07
multiphaseCavitation-vapourRho 0.02308
multiphaseCavitation-vapourNu 0.0004273
multiphaseCavitation-SchnerrSauer-n 1.6e+13
multiphaseCavitation-SchnerrSauer-dNuc 2e-06
multiphaseCavitation-SchnerrSauer-Cc 1
multiphaseCavitation-SchnerrSauer-Cv 1

When these parameters are omitted, default values are used.