Swept Attachment-line Boundary Layer Research Articles

Stability of the nonstationary swept attachment-line boundary layer with time variation of the surface temperature and gas suction velocity

The possibility of controlling the stability of a nonstationary boundary layer on the attachment line of a high-aspect-ratio swept wing by means of periodic variations of the surface temperature or the gas suction velocity at sub- or supersonic free-stream velocities is considered. The characteristic time scale of the variations of the surface temperature or the gas suction velocity on the attachment line is assumed to be equal to the characteristic aerodynamic time. On this assumption the stability characteristics of quasisteady attachment-line boundary layer flows are studied, the minimum values of the critical Reynolds numbers Re* of loss of stability are determined as functions of the temperature and the suction velocity, and examples of the periodic dependence of the surface temperature and the suction velocity for which, in the case of nonstationary flow, the time-average values of Re* exceed the analogous values for the steady-state boundary layer are constructed.

Numerical experiments on the stability of leading edge boundary layer flow: A two‐dimensional linear study

AbstractA numerical study is performed in order to gain insight to the stability of the infinite swept attachment line boundary layer. The basic flow is taken to be of the Hiemenz class with an added cross‐flow giving rise to a constant thickness boundary layer along the attachment line. The full Navier‐Stokes equations are solved using an initial value problem approach after two‐dimensional perturbations of varying amplitude are introduced into the basic flow.A second‐order‐accurate finite difference scheme is used in the normal‐to‐the‐wall direction, while a pseudospectral approach is employed in the other directions; temporally, an implicit Crank‐Nicolson scheme is used. Extensive use of the efficient fast Fourier transform (FFT) algorithm has been made, resulting in substantial savings in computing cost.Results for the two‐dimensional linear regime of perturbations are in very good agreement with past numerical and theoretical investigations, without the need for specific assumptions used by the latter, thus establishing the generality of our method.

Effect of surface temperature on the stability of the swept attachment line boundary layer

At fairly high Reynolds numbers instability may develop on the line of attachment of the potential flow to the leading edge of a swept wing and lead to a transition to boundary layer turbulence directly at the leading edge [1, 2]. Although the first results relating to the stability and transition of laminar flow at the leading edge of swept wings were obtained almost 30 years ago, the problem remains topical. The stability of the swept attachment line boundary layer was recently investigated numerically with allowance for compressibility effects [3, 4]. Below we examine the effect of surface temperature on the stability characteristics of the laminar viscous heat-conducting gas flow at the leading edge of a side slipping wing.

On the effect of wing taper and sweep direction on leading edge transition

Summary An experimental study has been made of the conditions necessary to produce transition in a swept attachment-line boundary layer which is subjected to disturbances from trip wires of various sizes. The boundary layer considered is that formed on a long, untwisted, tapered wing which has been tested in both the backward swept and forward swept configurations. Results from these tests are compared with previous work on an untapered model. Some important similarities and some puzzling differences have been found. Finally consideration is given to the practical implications of this work. It is suggested that a forward swept wing may be capable of supporting a laminar attachment-line flow at a much higher free-stream Reynolds number than a corresponding swept-back wing.

On the stability of an infinite swept attachment line boundary layer

The instability of an infinite swept attachment line boundary layer is considered in the linear régime. The basic three-dimensional flow is shown to be susceptible to travelling wave disturbances that propagate along the attachment line. The effect of suction on the instability is discussed and the results suggest that the attachment line boundary layer on a swept wing can be significantly stabilized by extremely small amounts of suction. The results obtained are in excellent agreement with the available experimental observations.

Comment on “Transition in the Infinite Swept Attachment Line Boundary Layer”

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Transition in the Infinite Swept Attachment Line Boundary Layer

SummaryThe transition behaviour of the boundary layer which is formed along an infinite swept attachment line has been studied experimentally. Circular trip wires and turbulent flat plate boundary layers have been used as sources of disturbance and the range of parameters covered has been such that the results are directly applicable to full scale flight conditions. Simple criteria have been deduced which allow the state of the boundary layer to be determined for given geometric and free stream properties. Sample calculations for typical swept wing configurations suggest that the majority of civil aircraft will have turbulent attachment lines in the cruise and that subsequent relaminarisation in regions of favourable pressure gradient is unlikely.