Performance Assessment of a Transonic Wing–Body Configuration with Riblets Installed

Abstract

The effectiveness of the riblets, one of the most interesting drag-reduction device, is discussed in this paper. Numerical simulations by the Reynolds-averaged Navier-Stokes equations with the riblets properly taken into account are presented. Riblets are modeled as a singular roughness problem by modifying the classical Wilcox boundary condition for rough walls. The boundary condition is able to predict the flow features in the low roughness range (transitional roughness) where riblets operate. A brief discussion of the simulations performed to validate the model is first presented. Then, a complex wing-body configuration is analyzed, and the overall effect of riblets on the aerodynamic coefficients is evaluated. Calculations of a complete aircraft configuration at transonic conditions show how a proper optimized choice of the riblet height can significantly improve the drag reduction.

Turbulent drag reduction over curved walls

“…This confirms the fundamental idea of recent works (see e.g. Mele, Tognaccini & Catalano 2016) where a RANS-based estimate of the reduction in the overall drag of a modern commercial aircraft covered by riblets was made. Such an estimate has a limited reliability (because of the RANS approach, and because riblets were accounted for indirectly via a modification of the turbulence model at the wall).…”

Performance Improvements of a Regional Aircraft by Riblets and Natural Laminar Flow

“…Then the model has been implemented in the CIRA in-house-developed UZEN code [19,20], a flow solver with a numerics and a data structure similar to FLOWer. A basic validation has been performed for a flat plate, and for 2D flows in previous papers [18,21,22,24,29], obtaining results consistent with theoretical considerations and in good agreement with the available experimental data. Accurate numerical computing and experimental measuring of small differences in drag coefficient is a critical issue, and then further 2D test cases are here presented and compared with available experiments.…”

“…The adoption in the simulation of the optimum l g value allows for a straightforward a posteriori calculation of the optimum physical size in the different aircraft parts. As verified in [39], the adoption of an average constant physical riblet height in each aircraft part does not significantly reduce the performance.…”

“…The proposed boundary condition has been implemented in two unsteady RANS (URANS) flow solvers, the Italian Aerospace Research Center (CIRA) in-house-developed UZEN code [19,20] and FLOWer, a code developed at German Aerospace Center (DLR) and used by University of Napoli. A relevant number of two-dimensional (2D) and three-dimensional (3D) test cases have been carried out in order to validate and evaluate the model [21][22][23][24].…”

Global energy fluxes in turbulent channels with flow control

“…For example the few existing drag-reduction-aware RANS turbulence models (e.g. Hassid & Poreh 1978;Mele et al 2016) are often based upon minor modifications of (the model equation for) that produce the desired skin-friction reduction effect. The present work has made evident how this approach may lack generality even for passive control.…”