Open AccessThe article presents the results of numerical investigation of kinetic energy (KE) loss and blading efficiency of the single-stage axial turbine under different operating conditions, characterized by the ratio u/C0. The calculations are performed by stationary (Stage method) and nonstationary (Transient method) methods using ANSYS CFX. The novelty of this work lies in the fact that the numerical simulation of steady and unsteady flows in a turbine stage is conducted, and the results are obtained to determine the loss of KE, both separately by the elements of the flow range and their total values, in the stage efficiency as well. The results obtained are compared with the calculated efficiency according to one-dimensional theory.
To solve these problems was selected model of axial turbine stage with D/l = 13, blade profiles of rotor and stator of constant cross-section, similar to tested ones in inverted turbine when = 0.3. The degree of reactivity ρ = 0.27, the rotor speed was varied within the range 1000 ÷ 1800 rev/min.
Results obtained allow us to draw the following conclusions:
1. The level of averaged coefficients of total KE losses in the range of from 0.48 to 0.75 is from 18% to 21% when calculating by the Stage method and from 21% to 25% by the Transient one.
2. The level of averaged coefficients of KE losses with the output speed of in the specified range is from 9% to 13%, and almost the same when in calculating by Stage and Transient methods.
3. Levels of averaged coefficients of KE loss in blade tips (relative to the differential enthalpies per stage) are changed in the range: from 4% to 3% (Stage) and are stored to be equal to 5% (Transient); from 5% to 6% (Stage) and from 6% to 8% (Transient).
4. Coefficients of KE losses in blade tips GV and RB are higher in calculations of the model stage using the Transient method than the Stage one, respectively, by = 1.5 ÷ 2.5% and = 4 ÷ 5% of the absolute values. These are values to characterize the KE loss because of unsteadiness influence.
5. The reduced efficiency due to influence of unsteady flow may reach a value of 4.8% (peak). This value is close to the maximum, since it corresponds to the minimum axial clearance Δz1 = 4 mm. An increased efficiency can be achieved by increasing the axial clearance. The solution to this and similar problems is possible through the use of the package ANSYS CFX.