The facility can perform both transient and continuous tests, suited for precise heat flux, efficiency, and optical measurement techniques to advance turbine aero-thermal-structural engineering. The PETAL facility comprises three test sections, offering a wide range of Technology Readiness Level (TRL) research opportunities.
Linear Experimental Aerothermal Facility (LEAF)
A) Bladeless turbines for power extraction from supersonic flows
Source: Braun J., Paniagua G., Falempin F., Le Naour B., 2019, “Design and experimental assessment of bladeless turbines for axial inlet supersonic flows”. Journal of Engineering for Gas Turbines and Power. November. https://doi.org/10.1115/1.4045359
An experimental campaign of a supersonic wavy surface that mimics the behavior of the bladeless turbine during supersonic operation was successfully demonstrated. The figure below depicts the supersonic test section, the wall pressure signature, in which the CFD is overlaid with the experiments. On the right side, the Schlieren results are visualized and the different shock structures are compared to the CFD.
B) Femtosecond laser electronic excitation tagging (FLEET)
Source: Fisher J., Braun J., Meyer T., Paniagua G., 2020, “Application of Femtosecond Laser Electronic Tagging Velocimetry in a bladeless turbine”. Measurement Science and Technology. Vol. 31, Number 6. https://doi.org/10.1088/1361-6501/ab7062.
The large velocity gradients in supersonic flows pose limitations on flowfield characterization using particle-based optical diagnostics, such as Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA). These limitations, along with challenges in seeding the flow, can be overcome by tracking the molecules already present in the flow. kHz-rate femtosecond laser electronic excitation tagging (FLEET) is demonstrated in this lab to excite long-lived fluorescence of nitrogen molecules, acting as in-situ flow tracers. A multi-point variation of this approach was demonstrated in LEAF. The femtosecond laser is coupled with an intensified CMOS camera with a frame rate of 200 kHz. High-speed measurements were made of the steady and unsteady performance in the bladeless turbine, with particular attention to capturing flow structures, spatial velocity gradients, and transient events such as unstarting of the supersonic passages.
C) High frequency heat flux sensor: Atomic Layer Thermopiles (ALTP)
The ALTP is a class of epitaxial films which generate voltage when exposed to a temperature gradient, greater than one can expect from the Seebeck coefficient. This voltage generation occurs at the molecular level making it ideal as a fast response heat flux sensor. ALTP can have a frequency response of 1 Mhz and have been successfully applied to detecting shocks and boundary layer fluctuations
Big Rig for Aerothermal Stationary Turbine Analysis (BRASTA)
A) Experimental Demonstration of Inverse Heat Transfer Methodologies for Turbine Applications
Gas turbines operate at extreme temperatures and pressures, constraining the use of both optical measurement techniques as well as probes. A strategy to overcome this challenge consists of instrumenting the external part of the engine, with sensors located in a gentler environment, and use numerical inverse methodologies to retrieve the relevant quantities in the flowpath. An inverse heat transfer approach is a procedure used to retrieve the temperature, pressure or mass flow through the engine based on the external casing temperature data. An improved Digital Filter Inverse Heat Transfer Method that consists of a linearization of the heat conduction equation using sensitivity coefficients was proposed. The sensitivity coefficient characterizes the change of temperature due to a change in the heat flux. This methodology was validated BRASTA annular wind tunnel, with flow temperatures up to 450K. Infrared thermography is used to measure the temperature in the outer surface of the inlet casing of a high pressure turbine. Surface thermocouples measure the endwall metal temperature. The metal temperature maps from the IR thermography were used to retrieve the heat flux with the inverse method. The inverse heat transfer method results were validated against a direct computation of the heat flux obtained from temperature readings of surface thermocouples.
B) Particle Image Velocimetry in a high-pressure turbine stage at aerodynamically engine representative conditions
Particle Image Velocimetry (PIV) is a well-established technique for determining the flow direction and velocity magnitude of complex flows and successfully tested in BRASTA to study a scaled-up turbine vane geometry within an annular cascade at engine-relevant conditions. Custom optical tools such as laser delivery probes and imaging inserts were manufactured to mitigate the difficult optical access of the test section and perform planar PIV. With the use of a burst-mode Nd: YAG laser and Photron FASTCAM camera, the frame straddling technique is implemented to enable short time intervals for the collection of image pairs and velocity fields at 10 kHz. Different Mach and Reynolds number operating conditions were achieved by modifying the temperature and mass flow. With careful spatial calibration, the resultant velocity vector fields are compared with Reynolds Averaged Navier Stokes (RANS) simulations of the vane passage with the same geometry and flow conditions. Uncertainty analysis of the experimental results is also presented and discussed, along with prospects for further improvements.
Small Turbine Aerothermal Rotating Rig (STARR)
The development of efficient small core turbines is critical as the aviation industry pushes to higher OPR engines, hybrid propulsion concepts, and multi-stream engines. In response to the small core advancement, the Small Turbine Aerothermal Rotating Rig was designed to address small core turbine challenges. Its two-stage turbine module is designed for continuous and transient operation, enabling precise efficiency and heat flux measurements. The test section is designed to test both uncooled and cooled geometries with 15 different cooling configurations. The modularity of the rig allows for experiments to be performed in any stator-rotor configuration. The rig is equipped with two traverse rings where different types of probes can be installed to measure temperature, pressure, flow direction and Mach number at several radial and circumferential locations in the inlet and exit planes of any configuration. In addition, specially designed blade track inserts allow for a wide range of instrumentation and optical measurement techniques at the rotor tip of both stages. This includes PIV, PSP, low/high frequency pressure sensors and tip clearance capacitance probes. These measurements will facilitate the detailed study of aero-thermal tip flows at various operating conditions.
The facility is complemented with a cooling auxiliary system which can provide multiple gases including N2, CO2 or dry air, providing coolant and control fluids with a large variability of density and blowing ratios. The energy extracted from the turbine is absorbed by a direct drive (no gearbox) high speed AC electric motor, enabling engine representative transient operation. The STARR test section, built in collaboration with Rolls-Royce, together with its auxiliary systems is the state-of-the-art facility to evaluate efficiency in small core turbines at a TRL of 5-6.
Turbine High pressure integrated Optical RDE (THOR)
In collaboration with Prof. Terry Meyer and Spectral Energy, the Turbine High pressure integrated Optical RDE (THOR) rig can be equipped with several classes of turbines to investigate to study combustor-turbine integration for advanced thermal cycles such as rotating detonation combustors.