Confluent Boundary Layer Research Articles

Wake-induced transition in the low-Reynolds-number flow over a multi-element airfoil

Abstract

Experimental Investigation of the Confluent Boundary Layer of a High-Lift System

This paper describes a fundamental experimental investigation of the confluent boundary layer generated by the interaction of a leading-edge slat wake with the boundary layer on the main element of a multi-element airfoil model. The slat and airfoil model geometry are both fully two-dimensional. The research reported in this paper is performed in an attempt to investigate the flow physics of confluent boundary layers and to build an archival data base on the interaction of the slat wake and the main element wall layer. In addition, an attempt is made to clearly identify the role that slat wake / airfoil boundary layer confluence has on lift production and how this occurs. Although complete LDV flow surveys were performed for a variety of slat gap and overhang settings, in this report the focus is on two cases representing both strong and weak wake boundary layer confluence.

Investigation of High-Lift Flowfield of an Energy Efficient Transport Wing

The high-lift flowfield around a multielement energy efficient transport wing is investigated both experimentally and numerically. Special emphasis is placed on resolving aeroacoustically relevant local features of the mean flowfield, e.g., separated flow regions including recirculation bubbles, free shear layers/wakes/jets, and vortices. Such features are typically present in slat and flap cove areas, flap side-edge regions, and slat-main-wing confluent boundary layer. The flow fluctuations sustained in these regions can generate significant noise, especially via interaction with nearby airframe structures. The experimental measurements and computed results presented here show excellent agreement for mean aerodynamic quantities and provide valuable physical insight into potential sources of flow unsteadiness, such as the vortex system near the flap side edge. Whereas the generic features of the computed flowfield are similar to other published studies, the specific details of the acoustically relevant flow features are found to depend on the geometry of the high-lift configuration

Experimental investigation of the confluent boundary layer of a high-lift system

Experimental investigation of the confluent boundary layer of a high-lift system

Investigation of Confluent Boundary Layers in High-Lift Flows

The confluent boundary layers over a three-element high-lift airfoil are studied using both numerical and experimental approaches. The results suggest that wake prediction is crucial to the convergence and accuracy of the overall solution. At maximum lift, unsteadiness is observed in the experiment, which is not captured by computations. However, solutions at maximum lift indicate that, although the flow is attached over the flap, the separation bubble at the leading edge of the slat upper surface is coupled with inviscid flow reaching the compressibility limit. The thickened slat wake results in a displacement of near-surface flow over the main element and limits the main element from gaining more lift. The trends in the confluent boundary layers development require all aspects of the physics be modeled appropriately, including transition, turbulence, and inviscid-viscous interaction

Algebraic turbulence modeling for unstructured and adaptive meshes

An algebraic turbulence model based on the Baldwin-Lomax model, has been implemented for use on unstructured grids. The implementation is based on the use of local background structured turbulence meshes. At each time-step, flow variables are interpolated from the unstructured mesh onto the background structured meshes, the turbulence model is executed on these meshes, and the resulting eddy viscosity values are interpolated back to the unstructured mesh. Modifications to the algebraic model were required to enable the treatment of more complicated flows, such as confluent boundary layers and wakes. The model is used in conjuction with an efficient unstructured multigrid finite-element Navier-Stokes solver in order to compute compressible turbulent flows on fully unstructured meshes. Solutions about single and multiple element airfoils are obtained and compared with experimental data.

Theoretical and Experimental Study of the Drag of Single- and Multielement Airfoils

The viscous/potential flow past single-element and multielement airfoils is studied theoretically and experimentally. A computerized analysis, based on iteratively coupled potential-flow and boundary-layer analysis, is used to predict the flowfield of the airfoil. The method yields detailed characteristics of conventional laminar and turbulent boundary layers, turbulent wakes, and confluent boundary layers. The viscous flows are analyzed with a method that uses finite-difference solutions of the boundary-layer equations. Reynolds stress in the boundary layers and wakes is simulated with eddy viscosity models for the various zones. The viscous calculations are carried into the wake of the airfoil where the drag is found from the defect in the wake momentum.

Analysis of High-Lift Wing Systems

SummaryA method which can be used for the design of blown or unblown wing sections is described in this paper. A brief description of a variety of theoretical methods for computation of different fluid flow phenomena encountered on high-lift wing systems is presented. The most significant type of viscous flow - a confluent boundary layer flow, which is present on the upper surface of the flap, the vane and the main component of a high-lift system – is described and its importance to the performance of high-lift systems is illustrated. Results of computation of pressure distribution, boundary-layer characteristic, and lift coefficient for two-dimensional high-lift systems are compared with experimental data in order to establish the validity and limitations of the method.

Parametric Relations for Ordinary and Confluent Turbulent Boundary-Layer Flows

Theme T paper presents the results of an investigation of parameters associated with the confluent boundary layer shown schematically in Fig. 1. It is shown that with a suitable choice of parameters, velocity profiles in both jet and wake layers become similar, with the same similarity function obtained for different pressure gradients. Moreover, local dynamic similarity allows suitable functional representation of shear stress at the loci of maximum and minimum velocity. Measured eddy viscosity distributions for the confluent boundary layer is presented for one velocity ratio at slot exit. An analytical solution for the conventional flat plate turbulent boundary layer is shown for comparison purposes.