Emerging technologies continually provide for improved measurements of complex flow phenomena. Techniques such as particle-image velocimetry and Doppler-based velocimetry yield detailed flow velocity measurements at scales needed in practical aerospace applications. Novel implementation of conventional approaches such as sonic anemometry and physical sensors have been enabled by new understanding gained from advanced instrumentation simulations. In this program, we seek fundamental development that advances the state-of-the-art for applied instrumentation approaches. The developments impact performance, efficiency and noise in propulsion, power and renewable energy technologies.
Aerodynamic modeling of high Reynolds number flows, while mature in many ways, suffers dramatic inaccuracies in complex cases such as separating flows. The origins of these deficiencies—turbulence and transition models—are themselves incomplete representations of the full physics and require quantitative insights from theory, fully-resolved simulations, and experiments. While experiments are often considered the standard against which to judge models, significant challenges exist in measuring the true boundary conditions present in any given study. These challenges have led many to suspect that unknown and uncertain experimental boundary conditions play a substantial role in the discrepancies between simulation and experimental results. Our team has focused on conducting combined experimental and computational studies with an emphasis on the stringent demands of computational model validation.
Modern tactical aircraft engines and future propulsion concepts for supersonic transport aircraft produce intense noise familiar to anyone who has attended an airshow. Well beyond the annoyance to the general public, crewpersons on aircraft carriers must work for extended periods in the region of most intense noise emissions of these aircraft. Sadly, these crewpersons can incur lifelong hearing damage from their service. In our program, we seek to obtain new information on the fundamental behaviors of high speed jets, supporting strategies to reduce noise via operational and design changes. Using a new flow diagnostics approach, information about the speed and intensity intermittent turbulent waves is obtained and interpreted based upon nozzle conditions and theory for jet noise radiation. A highlight of the effort is continuing development focused on large-scale applications including measurements in actual tactical aircraft engine exhausts.
Advanced aircraft concepts are increasingly reliant upon closer coupling of propulsion systems with airframe aerodynamics for optimal performance. A prime example is the NASA Hybrid Wing Body configuration, with some concepts employing boundary layer ingesting engines. While systems-level analysis can indicate that propulsive efficiency gains can result from tight integration, stream-wise vorticity invariably arises and greatly affects the performance of the propulsor. We have developed, in collaboration with Prof. Walter O’Brien, an advanced means for experimentally simulating the aerodynamics arising from engine/airframe integration. A 2000 lbf-thrust class turbofan engine is used for researching the development of vortical flow in the diffuser, as well as fan response to complex swirl and wake-like pressure distortions. The application was one of the first to demonstrate particle-image velocimetry for turbofan engine studies. Continuing developments have led to new understanding of the development and impact of complex inlet flows on turbofan engine performance and operability.