Turbulence Measurements and Analysis in a Multistage Axial Turbine

Abstract

This paper presents turbulence measurements and detailed flow analysis in an axial turbine stage. Fast response aerodynamic probes were used to resolve aperiodic fluctuations along the three directions. Assuming incompressible flow, the effective turbulence level and Reynolds stress are retrieved by evaluating the stochastic velocity component out of the measured time-resolved pressure and flow angle fluctuations along the streamwise, radial, and circumferential direction. A comparison between turbulence intensity and measured total pressure shows that flow structures with higher turbulence level are identified in the region of loss cores at the exit of the second stator passage. Turbulence intensity is evaluated under isotropic and nonisotropic assumption in order to quantify the departure from isotropic conditions. The measurements show that locally the streamwise fluctuating component can be twice bigger than the radial and tangential component. The current analysis shows that multisensor fast response aerodynamic probes can be used to provide information about the mean turbulence levels in the flow and the Reynolds stress tensor, in addition to the measurements of unsteady total pressure loss. Nomenclature c = absolute velocity vector e = mean unit vector in the secondary flow definition p = static pressure p d = dynamic head s, , r = streamwise, circumferential, and radial directions T=T 0 = blade passing period fraction t = time u = streamwise velocity component u,ṽ,w = periodic velocity component: phase-lock averaged u 0 , v 0 , w 0 = stochastic (aperiodic) velocity components v = circumferential velocity component w = radial velocity component = yaw angle = pitch angle x = absolute uncertainty of quantity x = density Subscripts/superscripts 1 = probe position 1 iso = isotropic assumption NS = nonsimultaneous sec = secondary flow vector

Effects of Inlet Turbulence and End-Wall Boundary Layer on Aerothermal Performance of a Transonic Turbine Blade Tip

“…As the now passes the downstream turbine vane passage, the turbulence level still remains high [4]. Porreca et al [5] measured the time average turbulence level which reaches a level up to 14% in the core of the secondary flows and the wake of the exit of the second stator.…”

A method for the determination of turbulence intensity by means of a fast response pressure probe and its application in a LP turbine

“…At the hub, the maximum value of u T is 14%, which is a typical value for secondary flows (see for example Porreca et al [9]). A particular interaction between secondary flows of stator and rotor may be identified in the three flow conditions.…”

“…Whereas, only recently, the use of fast-response aerodynamic pressure probes (FRAPP) has been extended to turbulence measurements. Porreca et al [9] and Persico et al [10] have recently shown that turbulence measurements may be performed with a two-sensor and one-sensor probe, respectively. In particular, the methodology proposed by Persico et al [10] may be adopted also for compressible flows, as performed by Paradiso et al [11] downstream of a transonic turbine rotor, where turbulence measurements by means of a FRAPP were validated with LDV.…”

Aerodynamics of wind turbine wakes in flat and complex terrains

“…In order to quantify the departure from isotropy, the degree of anisotropy (DA) is evaluated as [21].…”