Near-Field Interactions Element

The Near-Field Interactions element encompasses a broad range of analytical model-development and measurement activities. The prime objective of the measurements is to provide the detailed test data needed to assess the accuracy and completeness of the models. The combined goal of the modeling and measurement efforts is to describe and quantify the chemical and physical processes that occur in HSCT and subsonic-aircraft wakes during cruise operations. These processes occur in three identifiable regimes: engine exhaust-plume, wake-vortex, and vortex-breakup/wake-dispersion. The last regime, which typically extends to a distance of more than 20 km behind the aircraft in the case of subsonic civil transports, is where the engine exhaust gases or their chemical derivatives are mixed into the background atmosphere.

Through fiscal year 1996, approximately 53 percent of the funding allocated to this AEAP element has been expended or committed. The work planned for Near-Field Interactions is scheduled to be completed during fiscal year 2001. The funding available for the remaining five years of this element is on the order of $3.55 M.

ANALYTICAL MODEL DEVELOPMENT ACTIVITIES

A set of computer models is being developed to describe the fluid dynamic, chemical, and condensation processes that occur in each of the three exhaust-flow/atmospheric-mixing regimes behind the aircraft. As a part of the AESA project, some models of the regimes closest to the engine-exit plane were evolved. Models of the wake-dispersion regime (20 or more km behind the engine) are



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An Interim Assessment of AEAP's Emissions Characterization and Near-Field Interactions Elements Near-Field Interactions Element The Near-Field Interactions element encompasses a broad range of analytical model-development and measurement activities. The prime objective of the measurements is to provide the detailed test data needed to assess the accuracy and completeness of the models. The combined goal of the modeling and measurement efforts is to describe and quantify the chemical and physical processes that occur in HSCT and subsonic-aircraft wakes during cruise operations. These processes occur in three identifiable regimes: engine exhaust-plume, wake-vortex, and vortex-breakup/wake-dispersion. The last regime, which typically extends to a distance of more than 20 km behind the aircraft in the case of subsonic civil transports, is where the engine exhaust gases or their chemical derivatives are mixed into the background atmosphere. Through fiscal year 1996, approximately 53 percent of the funding allocated to this AEAP element has been expended or committed. The work planned for Near-Field Interactions is scheduled to be completed during fiscal year 2001. The funding available for the remaining five years of this element is on the order of $3.55 M. ANALYTICAL MODEL DEVELOPMENT ACTIVITIES A set of computer models is being developed to describe the fluid dynamic, chemical, and condensation processes that occur in each of the three exhaust-flow/atmospheric-mixing regimes behind the aircraft. As a part of the AESA project, some models of the regimes closest to the engine-exit plane were evolved. Models of the wake-dispersion regime (20 or more km behind the engine) are

OCR for page 10
An Interim Assessment of AEAP's Emissions Characterization and Near-Field Interactions Elements currently being developed. Also, as a result of the findings of the Concorde aircraft far-wake sampling experiment conducted with the NASA ER-2 aircraft, modeling efforts are being initiated to describe the particulate-formation processes that occur in aircraft wakes. To date, progress in validating any of these models has been constrained by a lack of available suitable datasets on near-field interactions. The capabilities and accuracy of these models are thus not well established at this time. Aggressive efforts to expedite the development and validation of this suite of computer models are recommended. At least first-cut versions of these individual models are required so that the important effort of integrating them can be initiated. Because of the complexity of these individual models and their likely interdependence, the integration task can be expected to be a challenging undertaking, possibly involving several iterations, before emissions can be ''tracked'' from the exhaust-plume through the wake-vortex into the wake-dispersion regime of the model suite. MEASUREMENT ACTIVITIES Flight-test programs to acquire near-field interaction measurements are in progress. One such program involves the use of the NASA Sabreliner as the airborne platform. Another involves participation in the AEAP Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS), which employs a DC-8 aircraft as the platform. Other aircraft platforms, including participation in the use of the NASA ER-2 aircraft, are being considered for use in future flight-test campaigns. The overall intent of these campaigns is to acquire quantitative measurements of the parameters shown in Table 2. The variety and sophistication of the instrumentation suites being used, or being considered for use, in these campaigns should enable them ultimately to yield extensive, high-quality datasets. These datasets are expected to be valuable for testing and validating the various analytical models that are currently being developed. Once successful measurements have been made, the promptest possible dissemination of the datasets to the interested modelers is recommended, both to expedite the execution of the individual model development and validation tasks and to permit the modeling community to identify possible additional test-data needs.

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An Interim Assessment of AEAP's Emissions Characterization and Near-Field Interactions Elements TABLE 2 Near-Field Observables, by Region Exhaust Plume Wake Vortex Vortex Breakup and Wake Dispersion NOx emission index (NOx/CO2) All measurements in exhaust-plume column plus: All measurements in wake-vortex column plus: SOx emission index (SOx/CO2) H2SO4/H2O condensation nuclei (number density, size distribution) Photochemistry of exhaust-rich region NOy speciation (NO, NO2, HONO, HNO3) Contrail droplet properties (number density, size distribution, composition) Particulate evolution SOx speciation (SO2, SO3, H2SO4, H2SO4 · nH2O) Contrail volume/shape   HOx speciation (OH, HO2, H2O2) Vorticity   Soot-particulate properties (number density, size distribution, hydration) Turbulence scale   Gas-temperature profiles     Exhaust-concentration profiles