IR-Signature of the MULDICON Configuration Determined by the IR-Signature Model MIRA

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German Aerospace Center *Remote Sensing Technology Institute Institute

1 DLR.de Folie 1 IR-Signature of the MULDICON Configuration Determined by the IR-Signature Model MIRA Erwin Lindermeir*, Markus Rütten DLR German Aerospace Center *Remote Sensing Technology Institute Institute of Aerodynamics and Flow Technology AIAA 2018, Atlanta, USA June 26, 2018

2 DLR.de Folie 2 Outline The IR-Signature Model MIRA Overview Application to IR-Signature Predictions for the MULDICON UCAV (NATO AVT-251) Summary

complex shaped exhaust duct and inlet Arbitrarily shaped exhaust gas

3 DLR.de Folie 3 IR-Signature Model MIRA Model for InfraRed Scene Analysis Requirements Modeling of emission and reflection Radiative transfer in complex shaped exhaust duct and inlet Arbitrarily shaped exhaust gas Interference of exhaust gas and flow around aircraft sensor sky ground surface cavity plume

DLR.de Folie 4 MIRA Reflections Method: Ray-tracing and Mote Carlo integration Direct irradiance (one reflection): Simple method: Directions of incidence from BRDF* OR radiance distribution on

4 DLR.de Folie 4 MIRA Reflections Method: Ray-tracing and Mote Carlo integration Direct irradiance (one reflection): Simple method: Directions of incidence from BRDF* OR radiance distribution on surfaces and integrate. sensor surface normal MIRA: Multiple importance sampling (MIS): Directions of incidence from BRDF AND radiance distribution on surfaces and weight contributions *BRDF = Bi-directional reflection distribution function half-space direct irradiance indirect irradiance

5 DLR.de Folie 5 Efficiency of Multiple Importance Sampling Cylinder (emissivity ε = 1, T = 400 K) in front of diffuse reflecting plate (ε = 0.6, T = 300 K) MIRA (simple) 256 rays per pixel, compute time: 22.5 s MIRA (MIS) 4 rays per pixel, compute time: 5.6 s

DLR.de Folie 6 Modeling Multiple Reflections Path-Tracing Construction of paths starting from the camera based on BRDF Bi-directional Path-Tracing Construction of

6 DLR.de Folie 6 Modeling Multiple Reflections Path-Tracing Construction of paths starting from the camera based on BRDF Bi-directional Path-Tracing Construction of sub-paths starting from the camera and from (strong) radiators Connection of sub-paths of various lengths Common Direct irradiance calculation at each intersection with geometry

7 DLR.de Folie 7 IR-Signature Model MIRA Further Capabilities Spectral Range: 2 20 µm Optimized sample generation: Low discrepancy sampler (and others) Interface to DLR TAU code to include CFD results (exhaust gas) Atmosphere and ground modeled by coupling to MODTRAN Terrain model to permit real landscape using a DEM (digital elevation model) and a surface classification. Output: Images, radiance spectra (a/c skin, exhaust duct, plume, background, ), contrast radiant intensity and irradiance

8 DLR.de Folie 8 MIRA IR-Signature Predictions to Improve the exhaust duct of MULDICON MULDICON Generic UCAV to demonstrate a multidisciplinary design approach Used in NATO AVT-251 and DLR project MEPHISTO MULDICON Courtesy of A. Schütte, DLR

9 DLR.de Folie 9 Exhaust Duct Outer Shape

10 DLR.de Folie 10 Temperature Distributions of Two Designs DLR-F17 bypass ratio 2 max. thrust 35 kn external mixing inlet MULDICON VCE*, max. bypass ratio 1.3 max. thrust 60 kn internal mixing inlet exhaust duct exhaust duct *VCE = variable cycle engine

11 DLR.de Folie 11 IR-Signature Comparison View from below View: Off-tail angle 30, elevation 25, distance 1 km, background clear sky Velocity Mach 0.8, altitude 11 km DLR-F17 MULDICON

12 DLR.de Folie 12 IR-Signature Comparison View from above View: Off-tail angle 30, elevation 25, distance 1 km, homogeneous background Velocity Mach 0.8, altitude 11 km DLR-F17 MULDICON

13 DLR.de Folie 13 IR-Signature of MULDICON at altitude 5 km Velocity Mach 0.8, distance 5 km, homogeneous background Off-tail angle 165, elevation 25 Off-tail angle 30, elevation 25

DLR.de Folie 14 MIRA s Terrain Model Purpose Improve realism by a structured background Current state First Version: DEM + Classification Scene: MULDICON in front

14 DLR.de Folie 14 MIRA s Terrain Model Purpose Improve realism by a structured background Current state First Version: DEM + Classification Scene: MULDICON in front of Mt. Brocken in the Harz area of Germany Data: DEM Area: 135 km x 110 km Classification derived from satellite data (Source: DLR s German Remote Sensing Data Center)

15 DLR.de Folie 15 Summary and Outlook IR-Signature Model MIRA Introduction of the IR-Signature Model MIRA Requirements, treatment of multiple reflections, terrain model MULDICON design Application of MIRA to aid the design (exhaust duct) by IR-signature predictions Result: Exhaust gas emissions minimized, but skin reflection/emission problematic Next Steps MIRA: Improved terrain model + structured sky (clouds) Investigations to lower the IR emission of MULDICON s airframe

Noordwich The Netherlands October, 21 th 22 th 2003

th Noordwich The Netherlands October, 21 th 22 th 2003 Page - 1 - Author: : Ralph Habig MSc for Aerospace Engineering Managing Director Europe Page - 2 - It is more and more common to use numerical analysis