Unsteady Transport Mechanisms in an Axial Turbine

Abstract

A numerical analysis using a commercial unsteady Navier–Stokes solver has been performed on a pin/blade configuration, in order to assess the efficacy of a commercial code in calculating time-periodic interactions and to gain a better understanding of the unsteady flow physics in axial turbines. Two cases have been investigated, with the pin positioned at 25 and 50 percent of true chord ahead of the leading edge. Both configurations have been computed both two and three dimensionally. The two-dimensional case was used to examine the influence of numerical parameters, such as mesh, time, and space discretization. The three-dimensional case allowed insight into the complete flow field including the wake influence on the secondary flow and mixing processes of the blade row. The basic mechanisms of the wake–blade interaction proved, as expected, to be the same for both pin positions. Yet, as the closest pin wake interaction with the blade field was much stronger, its features have helped to identify the respective roles of wake fluid transport and blade potential field for both cases. The latter effect, noticeably strong with the thick leading edge blade form presented in this study, has often been neglected, and this study helps shed new light on this phenomenon. The code used had been validated in previous work for pin-free steady flow within the same blade row and the new time-dependent case has served to confirm the code range and limitations. [S0889-504X(00)02104-8]

Three-dimensional unsteady investigation of HP turbine stages

“…In fact, using the perturbed velocity, the wake is represented by vectors pointing backward to the NGV vane. This effect, driven by the mass conservation principle is clearly observed from the perturbed velocity and it has been also described by Casciaro et al [19]. This apparent negative jet induces a mechanism of massflow feeding and discharging inside the rotor passage in regions where the wake is cut by the blade suction and pressure side.…”

Turbine Blade Tip Leakage Flow Control by Unsteady Periodic Wakes of Upstream Blade Row

“…According to Casciaro et al [10], the wake can be defined as any velocity deficit in the body-relative frame of reference occurring in a space much smaller than the one analyzed. If the instantaneous velocity field is decrease of the undisturbed value, a wake looks like a facing backward jet, which is the so-called "negative jet".…”