Experimental investigation of the interaction between showerhead coolant jets and main flow

Abstract

This paper presents the results of an experimental investigation into the thermal and aerodynamic behavior of coolant ejection at the leading edge of a highly loaded nozzle vane cascade. The leading-edge cooling scheme features four rows of cylindrical holes in a staggered configuration (showerhead). Pressure Sensitive Paints (PSP) technique was used to get the adiabatic film cooling effectiveness distribution, while Particle Image Velocimetry (PIV) and flow visualizations were used to investigate the mixing process taking place between coolant and main flow. PSP tests were conducted by using N2 (Density Ratio DR=1.0) as coolant at variable blowing ratio (BR=2.0-4.0). Further tests were run by using CO2 (DR=1.5) at matching BR and momentum flux ratio (I) in order to investigate the effects of density ratio. The BR = 3.0 injection case was selected for the PIV investigation. Thermal and flow field data consistently show a shift in the position of stagnation line towards the suction side. Jet liftoff close to stagnation and a strong jet to jet as well as jet to mainstream interaction were also observed, resulting in a complex 3D flow characterized by high turbulence levels with a high degree of anisotropy. No coherent structures were detected, supporting the random nature of mixing process.

Experimental investigation of the aerodynamic and thermal behaviour of the film at the leading edge of a cooled nozzle vane cascade

“…Flow filed measurements were performed by means of a Two-dimensional Particle Image Velocimetry (PIV) technique along four mutually perpendicular planes in an attempt to gain an almost 3D view of the investigated flow field. All the details about instrumentation, data processing, determination of flow statistics, and uncertainty estimation are available in Barigozzi et al (2019) and therefore are not reported for reason of shortness. Therefore, only the essential details that are necessary to understand the present results are provided in the following.…”

“…Highly spatially resolved PIV measurements were performed using air as coolant with variable injection conditions corresponding to BR = 2.0, 3.0 and 4.0. Data belonging to the BR = 3.0 case have been the object of a specific paper (Barigozzi et al, 2019)). Some of these data are used here as a reference.…”

Numerical evaluation of heat/mass transfer analogy for leading edge showerhead film cooling on a first-stage vane

“…In the present work, the influence of coolant properties on leading film cooling has been examined through the use of different foreign gases (nitrogen and carbon dioxide). The computational approach was used to supplement the experimental investigation reported in [14], where  measurements in the leading edge region of a realistic, high pressure vane were performed using Binary PSP at DR values of about 1 and 1.5, matching either BR or I. The appropriate scaling parameter is another open question for the showerhead region: adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with I for high blowing conditions according to Ethridge et al [15].…”