Secondary Flow Structures and Losses in a Radial Turbine Nozzle

Abstract

An analysis of secondary flow structures and losses in a variable-vane radial turbine geometry is provided based on CFD. A complete turbine stage of a commercial vehicle turbocharger is modeled, including the entire 360° rotor and stator, in order to account for the circumferential non-uniformity of the flow. The full-stage model consists of approximately 12,500,000 nodes. The stator domain accounts for the endwall clearance on the hub side of the nozzle vanes. As an additional feature typical for variable turbine geometries, cylindrical shaft seals at the stator vane axis at hub and shroud as well as four circumferentially equidistant spacers are modeled. These geometrical details allow a more realistic simulation of the stator domain. In an analysis using fields of helicity and Q-Criterion, the present features are found to induce additional secondary vortices in the stator, in addition to the inflow and horse shoe vortices found by previous investigators. A detailed analysis of the secondary flow structures in this realistic stator shows that the spacers contribute 33% to the overall stator losses.

Understanding of the Interaction between Clearance Leakage Flow and Main Passage Flow in a VGT Turbine

“…The work of Roumeas and Cros [3] also indicated that the clearance leakage leads to the development of vortices along the nozzle vane chord that tends to increase the total pressure loss in the nozzle. Natkaniec et al [11] performed a numerical research of secondary flow structures and losses in a turbine with realistic vanes and found that some typical vortices generate a lot of flow loss in stator. A two-dimensional nozzle vane generates a straight wake in the downstream region of trailing edge.…”

Loss analysis of the shrouded radial-inflow turbine for compressed air energy storage

“…The stator loss accounts for about 9.8% of overall turbine stage loss, and it could be up to 14.8% considering the spacer. Detailed loss analyses in stator could be found in Putra and Joos, 32 Natkaniec et al 33 and Simpson et al 34 The accumulation of loss in the mainstream passage at the designed condition is shown in Figure 5.…”

“…The local peak of the total pressure loss coefficient, which is associated with the inflow vortex and corner vortex, appears at the stator suction side. Some full-stage numerical simulations 33,34 also successfully captured the horse shoe vortices, inflow vortices and corner vortices. The stator loss accounts for about 9.8% of overall turbine stage loss, and it could be up to 14.8% considering the spacer.…”

Aerodynamic Design and Numerical Analysis of Supersonic Turbine for Turbo Pump

“…Thus, helicity was introduced to discern the secondary flow vortex and study the flow field in the vane. The helicity is the scalar product of the vorticity vector and the velocity of flow, which is also used by Torre [18], Anker [19] and Natkaniec [20] in their study to analyze the complex flow field caused by the secondary flow. In order to understand the evolution of secondary flow vortex in the passage, contours of helicity and isolines of stagnation pressure recovery coefficient are showed in a set of cross section, which locate at 5% C x upstream of the blade leading edge, 30%, 60%, 90% and 120% downstream of the blade leading edge successively.…”