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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2018

Some General and Fundamental Requirements for Designing Observing System Simulation Experiments (OSSEs)

There is an increasing demand to provide OSSE support when seeking funding for new atmospheric observing instruments. Various individuals and groups are running or developing OSSEs with little experience in OSSEs in particular or DA in general. In this presentation we will describe some key issues that are often neglected and some of the poor practices to be avoided. These include issues regarding NR and OSSE validation, consideration of instrument, observation operator, and forecast model error, relationships between observations and synoptic conditions, and conflicts of interest.

Errico, Ronald M.↗
NASA NTRS2018

Fundamental Study of a 7-Element Fuel Injector Configuration for Gas Turbine Combustors, a Look at Cold Flow and Burning Measurements

As part of a parametric study in which we vary swirler angle and orientation and look at their effect on fluid mixing and combustion, we examine one configuration of a 7-point lean direct injector by looking at the non-combusting 2-D velocity field using PIV (Particle Image Velocimetry), and combusting system for chemical species using chemiluminescent imaging and flame spectroscopy. The circular 7-point array consists of axial swirlers, with the center 60 degree counterclockwise swirler surrounded by six 52 degree clockwise swirlers. The velocity results for this configuration show that the outer swirlers serve to isolate the center flow field near the injector exit. A recirculation zone forms downstream of the center swirler, but not behind the outer swirlers. The combusting results also show an isolated zone directly downstream of the center injector. The flame spectra show variation in speciation of combustion species such as OH* and CH*, and as a function of position within the combustor.

lean direct injection↗
NASA NTRS2018

Fundamental Study of a 7-Element Fuel Injector Configuration for Gas Turbine Combustors - A Look at Cold Flow and Burning Measurements

Lean direct injection (LDI) is a combustion concept to reduce oxides of nitrogen (NOx) for next generation aircraft gas turbine engines. These newer engines have cycles that increase fuel efficiency through increased operating pressures, which increase combustor inlet temperatures. NOx formation rates increase with higher temperatures, and the LDI strategy is to avoid high temperature by staying fuel lean and away from stoichiometric burning. Thus, LDI relies on rapid and uniform fuel/air mixing. Additionally, in combustors for smaller core engines, the area and volume bring about mixing and time scale challenges not found in larger engines. As part of our parametric study in which we vary swirler angle and orientation and look at their effect on fluid mixing and combustion, we examine one configuration of a 7-point lean direct injector by looking at the non-combusting 2-D velocity field using PIV, and combusting system for chemical species using chemiluminescent imaging and flame spectroscopy. The circular 7-point array consists of axial swirlers, with the center 60° swirler surrounded by six 52° swirlers. The velocity results for this configuration show that the outer swirlers serve to isolate the center flow field near the injector exit. A recirculation zone forms downstream of the center swirler, but not behind the outer swirlers. The combusting results also show an isolated zone directly downstream of the center injector. The flame spectra show variation in speciation of combustion species such as OH*, C3*, CH*, and C2* as a function of position within the combustor.

lean direct injection↗
NASA NTRS2018

Fundamental Study into Rotor Outwash and Dust Kick-up under Mars-like Conditions

Humans have reached a limit to how much information can be collected from a purely ground-based rover exploration mission on Mars. Therefore, an airborne mission would broaden our knowledge of this planet and at the same time it would allow for a different approach to scientific research. Thus, the Mars Helicopter Scout (MHS) Project was founded. However, as this is only a technology demonstrator, its first and short-term goal is to fly in the vicinity of the Mars Rover and assess where the rover can go. This would reduce the risk of damage to the rover and allow for minimum transit times on the Martian surface. The main objective of the project is conducting small-scale hover testing of a coaxial rotor system in- and out-of-ground effect to study both rotor downwash/outwash and to examine the conditions under which dust kick-up and brownout does or does not occur under Mars-like conditions, with potential application to Mars Helicopter development. Given the exploratory nature of this project, it is limited to a proof of concept of testing techniques that may eventually be used on the full scale MHS. These future tests will help determine whether or not dust kick-up can pose a problem on the performance of the MHSs altimeter.

Saltation↗
NASA NTRS2019

Scale–Resolving Simulations of a Fundamental Trailing–Edge Cooling Slot Using a Discontinuous–Galerkin Spectral–Element Method

The accurate prediction of turbulent mixing in high-pressure turbines that incorporate various airfoil surface-cooling strategies is becoming increasing critical to the design of modern gas turbine engines where the quest for improved efficiency is driving compressor overall pressure ratios and turbine inlet temperatures to much higher levels than ever before. In the present paper, a recently developed computational capability for accurate and efficient scale–resolving simulations of turbomachinery is extended to study the turbulent mixing mechanism of a simplified abstraction of an airfoil trailing-edge cooling slot - a plane wall jet with finite lip thickness discharging into an ambient flow. The computational capability is based on an entropy– stable, discontinuous–Galerkin approach that extends to arbitrarily high orders of spatial and temporal accuracy. The numerical results show that the present simulations capture the trends observed in the experiments. Discrepancies between the simulations and experiments are believed to be due to differences in the inflow profiles and tunnel side–wall effects. The thick lip configuration leads to a thicker wake and higher unsteadiness in the wall jet compared to the thin lip. A detailed comparison of the turbulent flowfields is presented to highlight differences arising due to lip thickness variations.

Scale Resolving↗

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