A review of methods for assessing loss coefficients in radial gas turbines

Design and performance prediction of radial ORC turboexpanders

“…They are generally based on experimental data and make use of equations for stationary ducts. Referring to the experimental tests of Hiett and Johnston, Benson determined the stator loss coefficients (n N ¼ 0:05-0:15) [26], showing that they are very small compared to the corresponding values in the rotor. For the estimation of stator losses, it is possible to apply Rodger's correlation [15]:…”

“…Friction losses can be estimated referring to a rotor-equivalent duct working on the same flow rate [26]:…”

“…The stator losses, which are generally lower than the rotor losses, have been often evaluated with less accuracy in the literature [15,26]. They are generally based on experimental data and make use of equations for stationary ducts.…”

“…For this reason, the incidence loss appears. The recommended models for the estimation of rotor incidence loss were developed at NASA [15,16,26]. The general approach is to assume that the kinetic energy associated with the variation of the tangential component of the relative velocity with respect to the design value, which is the result of the fluid-blade impact, is converted in internal energy of the fluid, which leads to an increase of entropy.…”

“…This may not be a satisfactory approximation when dealing with ORC turbines, which operate near the saturation line or close to the critical point. In the model hereafter proposed, correlations from literature are used [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], but real Equations Of State (EOS) are applied to the expansion process (static and total variables) in place of ideal gas relations. This is an important feature, allowing to preliminary design and performance prediction of turbo-expanders that work with real substances.…”