Effects Of System Rotation Research Articles

DNS Algorithm for Homogeneous Decaying Turbulence Subjected to System Rotation.

A new algorithm for simulating homogeneous decaying turbulence in an incompressible fluid subjected to uniform system rotation has been proposed. The complex helical waves decomposition is introduced to diagonalize the Coriolis term of the Navier Stokes equations in the Fourier space. The integral factor technique has been extended to the Coriolis term. Since the Coriolis term is integrated analytically in the algorithm, time increment is not restricted by the system rotation. It is proved that the new algorithm is effective at high rotation rate. The effect of system rotation is observed clearly in high rotation cases. It is also indicated that the energy spectrum depends on the modulus of wave vector κ and cos θ, where θ is the angle between the rotation vector Ω and the wave vector κ.

Effects of System Rotation on Turbulence Structure:A Review Relevant to Turbomachinery Flows

Turbomachine rotor flows may be affected by system rotation in various ways. Coriolis and centrifugal forces are responsible for (i) modification of the structure of turbulence in boundary layers and free shear layers, (ii) the generation of secondary flows, and (iii) “buoyancy” currents in cases where density gradients occur. Turbulence modification involves reduction (stabilization) or increase (destabilization) of turbulent Reynolds stresses by Coriolis forces; effects which areof special importance for the understanding and prediction of flows in radial and mixed flow pump and compressor rotors. Stabilization/destabilization effects are discussed by a selective review of the basic research literature on flows in straight, radial, rotating channels and diffusers.

Closure to “Discussions of ‘Effects of System Rotation on the Performance of Two-Dimensional Diffusers’” (1976, ASME J. Fluids Eng., 98, p. 429)

Closure to “Discussions of ‘Effects of System Rotation on the Performance of Two-Dimensional Diffusers’” (1976, ASME J. Fluids Eng., 98, p. 429)

Effects of System Rotation on the Performance of Two-Dimensional Diffusers

Experiments with incompressible flow are reported concerning the effects of Coriolis acceleration on flow separation and on separated flow in plane-wall diffusers of rectangular cross section. The diffusers were rotated about an axis perpendicular to the plane of the nearly two-dimensional flow in order to simulate some features of the blade-to-blade flow distribution in the radial portion of the centrifugal impeller. Various stall regimes are mapped on coordinates of rotation number and diffuser area ratio (at fixed wall length). Diffuser pressure-recovery coefficient is reported as a function of area ratio and rotation number. These data demonstrate that, by suppressing turbulent mixing and shear stress in the suction-side boundary layers, the Coriolis acceleration field greatly enhances the tendency for stall to appear in a diffuser. This effect causes a corresponding reduction in the throat-to-exit pressure recovery as compared to that of nonrotating diffusers of the same geometry and inlet flow blockage.