PIV and Rotational Raman-Based Temperature Measurements for CFD Validation in a Single Injector Cooling Flow

Abstract

Film cooling is used in a wide variety of engineering applications for protection of surfaces from hot or combusting gases. The design of more efficient thin film cooling geometries/configurations could be facilitated by an ability to accurately model and predict the effectiveness of current designs using computational fluid dynamics (CFD) code predictions. Hence, a benchmark set of flow field property data were obtained for use in assessing current CFD capabilities and for development of better turbulence models. Both Particle Image Velocimetry (PIV) and spontaneous rotational Raman scattering (SRS) spectroscopy were used to acquire high quality, spatially-resolved measurements of the mean velocity, turbulence intensity and also the mean temperature and normalized root mean square (rms) temperatures in a single injector cooling flow arrangement. In addition to flowfield measurements, thermocouple measurements on the plate surface enabled estimates of the film effectiveness. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 68.07 mm square nozzle blowing heated air over a range of temperatures and Mach numbers, across a 30.48cm long plate equipped with a single injector cooling hole. In addition, both centerline streamwise 2-component PIV and cross-stream 3-component Stereo PIV data at 15 axial stations were collected in the same flows. The velocity and temperature data were then compared against Wind-US CFD code predictions for the same flow conditions. The results of this and planned follow-on studies will support NASA's development and assessment of turbulence models for heated flows.

PIV and Rotational Raman-Based Temperature Measurements for CFD Validation of a Perforated Plate Cooling Flow: Part I

“…The rms levels are similar to those expected at the end of a potential core for a simple jet exhausting into ambient. A similar trend was observed in the THX Step III PIV data (Wernet et al, 2018) where the rms velocity levels along the jet centerline increase with distance but the normalized rms temperature values approach a constant value independent of axial location.…”

“…Recently, this new temperature data set enabled assessment of LES predictions of flow velocity, turbulence, mean temperature and rms temperature (DeBonis, 2017). In Step III of the THX task, both velocity field and temperature data were acquired for a cooling configuration with a relatively large single cooling hole (Wernet et al, 2018). The geometry was simple enough to permit detailed velocity and temperature measurements (mean flow and turbulence) to characterize the fluid dynamics and thermodynamics in the vicinity of the interaction region between the hot main flow stream and the injected cooling flow.…”

“…Baldauf et al, (2001) used IR cameras to estimate adiabatic film cooling effectiveness over a range of inclination angles, hole pitch and blowing ratios, where again the 30° inclination angle and BR ≈ 0.5 were determined to be optimal. Wernet, et al, (2018) were the first to use Particle Imaging Velocimetry (PIV), Rotationally Resolved Raman scattering, and embedded thermocouples to characterize both the flow field velocity and gas temperature of a single jet issuing into a heated freestream flow above a flat plate at elevated velocities (Mach 0.3 to Mach 0.9) and temperatures (up to 950 K) over a range of BR's. The PIV and Raman temperature measurements clearly depicted the lift-off of the injected plume and defined the mixing layer between the hot freestream flow and the injected film cooling flow.…”

“…CFD predictions at transonic speeds and high temperatures are handicapped by a lack of experimental data available to validate results, except for the work of Wernet et al, (2018). The typical industrial practice utilizing a RANS approach, employs a linear two-equation turbulence model, and a constant turbulent Prandtl number, Prt, to calculate the turbulent heat flux terms in the energy equation (Yoder, 2016).…”

Raman temperature and density measurements in supersonic jets

“…Vibrational Raman is ineffective in low temperature regimes due to the lack of the anti-Stokes bands; however, pure rotational Raman spectroscopy, which is not dependent upon anti-Stokes lines, has been used to interrogate expanding supersonic flows of CO 2 for measuring temperature (Maté et al 1998). Rotationally resolved Raman has more recently been used to acquire mean and rms temperature measurements in high-temperature flows, from subsonic to supersonic speeds in harsh real-world test facilities (Locke et al 2017;Wernet et al 2018Wernet et al , 2019Wernet et al , 2020. Rotationally resolved Raman scattering is the only technique which is relatively simple to setup/align and robust against the hostile environments found in real-world aerospace simulation facilities; therefore, it was the technique of choice for measuring the gas temperatures in supersonic jet flows of interest.…”