Patrick Magari

Thermophotovoltaics for Space Power Applications

Thermophotovoltaic (TPV) energy conversion has long been considered a potential replacement for thermoelectrics in radioisotope powered deep space power systems. In this application, TPV offers significant potential improvements in both efficiency and mass specific power (W/kg), performance which is considered mission enabling for a variety of mission concepts. TPV systems powered by concentrated solar energy have also been proposed for inner planetary solar system missions. This concept takes advantage of TPV’s ability to store energy for shadow periods in the form of heat energy rather than as electrical energy (batteries), as is commonly done for photovoltaic power systems. The simplicity and large number of power cycles offered by the thermal energy storage offers potential system benefits compared to a photovoltaic / battery system. Recent efforts in the development of radioisotope TPV (RTPV) at Creare have resulted in the demonstration of converter efficiencies in excess of 19%. Several independent ...

Thermal spray approach for TPV emitters

We have fabricated selective emitters and systematically investigated their performance in comparison with a gray body (SiC-based composite) emitter. The two key elements of our approach are (1) using thermal-spraying to manufacture thin-film selective emitters, and (2) exploring a variety of oxide materials, including rare-earths (erbia, thulia, and holmia) and cobalt-doped spinel. We fabricated the emitters by plasma-spraying coatings at thicknesses ranging from 15 to 250 microns. The spectral emittance was measured as a function of wavelength for each of the various types of emitters. Our plasma-sprayed, composite emitters are able to operate at temperatures as high as 1760 K. We find that the selective emission characteristics of the oxides are retained through the plasma-spray process. The emittance of the supporting components in the composite emitter structure is the key to the performance of these selective emitters. We investigated the use of reflective metal layers and various substrates (alumin...

Effect of Pulsed Plasma Jets on Boundary Layer Recovery Downstream of a Reflected Shock Wave-Boundary Layer Interaction

Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic inlets including flow instability, fatigue of structural panels, poor pressure recovery, flow distortion, and unstart. The current study investigated the effect of pulsed plasma jets on the recovering boundary layer downstream of a reflected shock wave-boundary layer interaction at several run conditions. Three actuator configurations were tested: 20◦ pitch, 0◦ skew, 1.8 mm exit diameter; 20◦ pitch, 0◦ skew, 2.5 mm exit diameter; and 40◦ pitch, 45◦ skew, 2.5 mm exit diameter. The actuators were tested with pulsing frequency of 700 Hz, 1000 Hz, 1500 Hz, 2000 Hz and 3000 Hz. The jet exits were placed at a distance of 5 mm from the separated region. A traversable pitot probe is used to measure the velocity profile of the boundary layer 35 mm downstream of the plasma jets, and the degree of boundary layer distortion is compared between the different models and run conditions. Additionally, the effect of each actuator configuration on the shape of the mean separated region is investigated using surface oil flow visualization. Measurement results are compared to unsteady RANS simulations of pulsed and steady jets interacting with a shock-separated flow. It was found that at a forcing frequency of 2000 Hz, the large exit diameter 20◦ pitch jet locally displaces a section of the mean separation line by approximately 30% of the scale of the separated region, and all configurations locally displace the mean separation line by 10-15% of the separation scale. However, very little effect is seen in the downstream recovering boundary layer. Immediately downstream of reattachment, shape factor, displacement thickness and friction coefficient seem to be shifted by 2-3%, but this is within measurement uncertainty. The wake parameter is more affected, shifting by as much as 10%, just outside measurement uncertainty. Far downstream, any observable effects are gone except for a weak shift in wake strength. Comparison with the simulations suggest that this is at least partially due to insufficient heating of the gas in the jet cavity by the electrical discharge.

TDLAS Measurements of Multiple Species and Temperature of Augmented Aeroengines

Zolo Technologies has recently completed the development of a prototype wavelengthmultiplexed tunable diode laser spectroscopy (WM-TDLAS) measurement system to monitor multiple species (H2O, CO2, CO, O2, and NO2) and temperature, T(K) in the exhaust plume of augmented aeroengines. The system has been utilized in several field demonstration test measurements on military engines. The goals for the system are to demonstrate a means of diagnosing and monitoring unstable combustion phenomena such as screech and to develop an alternative to gas sampling rakes for emissions testing for engines. A further goal is to develop the capability to measure these species, and particularly temperature, with two-dimensional spatial resolution at the engine exit for quickly identifying detrimental and dangerous engine operating conditions such as hot streaks without having to disassemble the engine or even remove it from the airframe. Although work remains, great progress has been made on each of these goals.

Design and testing of a wavelength-multiplexed TDLAS sensor for augmentor performance using an immersed water-cooled probe

A traversable, in-situ, water-cooled probe was designed, built, and tested to make tunable diode laser temperature measurements in a bluff-body stabilized flame simulating a jet engine augmentor. The combusting flow field was characterized by a Reynold’s number of 15,000 for all experiments, clearly in the turbulent regime. Two stability conditions have been documented for such flows previously, stable and unstable. The stable flow is characterized by small Kelvin -Helmholtz vortices relative to the size of the bluff body. In the unstable regime near the lean extinction limit, the flow becomes unstable displaying large-scale Karmen-Street vortices. We have, for the first time, performed high speed (up to 1 kHz) temperature measurements in such a flow field with approximately 2.5 cm spatial resolution. The results show large temperature fluctuations in the unstable regime near lean extinction as expected.