Control of laminar breakdown in a supersonic boundary layer employing streaks

In this study direct numerical simulations are employed to investigate the effects of various parameters on the laminar-flow-control capabilities of narrowly spaced streaks in a supersonic boundary layer at Mach $2.0$ . Previous work by Sharma et al. (J. Fluid Mech., vol. 873, 2019, pp. 1072–1089) has found these streak modes, excited by a spanwise blowing-and-suction strip, to be highly effective at delaying pure oblique-type breakdown. In the present work it is shown that spectrum-enriching subharmonic modes, relevant with increasing running-length Reynolds number, do not destroy the controlling mechanism, and also a complex breakdown scenario, triggered by a multi-frequency point source, is found to be effectively controlled. Moreover, the control-streak excitation by roughness elements is compared in detail with the blowing-and-suction method, revealing relevant differing features.

Experimental investigation of hybrid laminar flow control by a modular flat plate model in the DNW-NWB

To determine the characteristics of new suction concepts for hybrid laminar flow control (HLFC) a modular flat plate wind tunnel model is investigated in the DNW-NWB wind tunnel facility. This approach allows detailed examination of suction characteristics in consideration of realistic boundary layer flow conditions. The following evaluation reveals the effects of joining methods between successive panels and other surface disturbances of porous materials and underlying chambers on HLFC techniques. After successful measurements with and without suction panels, this paper compares experimental results with theoretical and numerical approaches and draws conclusions from N-factor results and boundary layer (BL) measurements.

Concept and design of extended hybrid laminar flow control suction panels

Fully laminar aircraft are one step towards reaching eco-efficient aviation. However, high system complexity and significant manufacturing effort prevent the wide usage of existing laminarisation concepts such as laminar flow control, which are rarely found in commercial aircraft. Hybrid laminar flow control concepts reduce the manufacturing effort significantly at the cost of only achieving partial laminar flow. This paper presents extended hybrid laminar flow control concepts for fully laminar wings, with reduced system complexity. A detailed study of structural and aerodynamic requirements provides the foundation for partial design solutions of active suction structures. The authors derive two concepts for active suction panels from the structural design space. While the first concept relies on state of the art manufacturing techniques, the focus of the second concept is on additive manufacturing technologies. Based on these concepts, it is feasible to design fully laminar wings with structurally integrated active suction systems. The authors propose an aerodynamic test strategy for further developing extended hybrid laminar flow control.

Development of a Multi-Segment Parallel Compressor Model for a Boundary Layer Ingesting Fuselage Fan Stage

The present methodological study aims to assess boundary layer ingestion (BLI) as a promising method to improve propulsion efficiency. BLI utilizes the low momentum inflow of the wing or fuselage boundary layer for thrust generation in order to minimize the required propulsive power for a given amount of thrust for wing or fuselage-embedded engines. A multi-segment parallel compressor model (PCM) is developed to calculate the power saving from full annular BLI as occurring at a fuselage tail center-mounted aircraft engine, employing radially subdivided fan characteristics. Applying this methodology, adverse effects on the fan performance due to varying inlet distortions depending on flight operating point as well as upstream boundary layer suction can be taken into account. This marks one step onto a further segmented PCM model for general cases of BLI-induced inlet distortion and allows the evaluation of synergies between combined BLI and active laminar flow control as a drag reduction measure. This study, therefore, presents one further step towards lower fuel consumption and, hence, a lower environmental impact of future transport aircraft.

HLFC-optimized retrofit aircraft design of a medium-range reference configuration within the AVACON project

This paper presents an approach for the design of a retrofit aircraft with integrated, optimized hybrid laminar flow control (HLFC). The basis for this research is a medium-range reference configuration derived within the German LuFo project “Advanced Aircraft Concepts” (AVACON). For the aerodynamics, an in-house-developed process chain for flow analysis is used, which requires airfoil shapes at specific sections of a known wing geometry. To improve the accuracy, pressure distributions from the 2D flow solver MSES are first aligned to high-fidelity 3D results from DLR’s TAU code for extracted airfoils. This is done by varying parameters of the transformation methods used. Subsequently, the required suction distributions are optimized based on pre-defined criteria; these include not only the aerodynamic effects but also the needed mass flows. After optimizing the HLFC system architecture concerning mass and power offtakes, a retrofit aircraft is designed with the in-house “Multidisciplinary Integrated Aircraft Design and Optimization” (MICADO) environment. Compared to the turbulent baseline, the promising potential of the HLFC technology is demonstrated. In addition, the actual benefit of the optimization approach is evaluated in the context of overall preliminary aircraft design. This is done by redesigning the aircraft with other suction distributions and HLFC system architectures. Although it is shown that the approach leads to an overall optimum, the optimization benefit remains small. This indicates the limits of the HLFC technology as a pure add-on for initially turbulent aircraft and the need for the application of new laminar wing design methods to tap the full potential of HLFC.