Flow Control Studies for Military Aircraft Applications

Laminar Flow Control - Back to the Future?

“…Perhaps of more practical interest to the aircraft designer is the fact that Eq. (21) shows that, by applying appropriate suction, a laminar boundary layer with a convex velocity profile can be maintained in a region of decelerating flow.…”

“…The ability to achieve laminar flow by the application of suction over the forward part of a surface has been demonstrated in flight on a number of aircraft, most recently on an Airbus A320 fin and a Boeing 757 wing. There are many engineering and operational obstacles to overcome 4 before either form of laminar flow control is adopted in the design of a new transport aircraft project, not least being the development of lightweight and efficient suction systems 21,22 . The risk of loss of laminarity due to insect contamination should be less than for NLFC aircraft but the issue of the impact on weight of carrying additional reserve fuel as a precaution against loss of laminarity needs to be resolved for HLFC, just as ‡ I am grateful to Peter Wong of ARA for providing these results, derived using the well validated BVGK aerofoil design code 29 as further developed at ARA to apply to aerofoils with suction.…”

Civil aviation and the environment – the next frontier for the aerodynamicist

“…Today, the measures needed to avoid leading-edge contamination are well understood and the other two types of instability can be modelled satisfactorily for aerodynamic design purposes by linear stability theory (36) and, if necessary, suppressed by boundary-layer suction as discussed for example by Wong and Maina (37) and Schrauf (38) . Since my purpose is to discuss only the basic nature of the constraints facing the aerodynamic designer, I shall consider only the nature and suppression of the Tollmien-Schlichting instability in the two dimensional laminar boundary-layer.…”

“…In fact, whilst most early modelling of wings with HLFC envisaged suction as an extension to the aerodynamic design concepts developed for NLFC, with suction supplementing the effect of gently accelerating flow over the forward part of the aerofoil, recent studies by Wong and Maina (37) have pointed in a different direction. Their work has shown that, for a given energy into the suction system, a greater performance benefit can be obtained for aerofoils with an adverse 'rooftop' pressure distribution, similar to that adopted for modern designs with fully turbulent boundary layers, rather than the flat or favourable pressure distributions that were traditionally thought appropriate for laminar flow applications.…”

Air Travel – Greener by Design Mitigating the environmental impact of aviation: Opportunities and priorities

“…Wing design philosophy has a part to play in selecting a design which remains aerodynamically efficient in this event. Recent work by Wong and Maina (17) has shown that, for a given energy into the suction system, a greater performance benefit can be obtained for aerofoils with an adverse 'rooftop' pressure distribution, similar to that adopted for modern designs with fully turbulent boundary layers, rather than the flat or favourable pressure distributions which have traditionally been thought appropriate for laminar flow applications. The rules governing the commercial operation of a hybrid laminar flow control aircraft are not yet defined, but it is possible that they will require an additional reserve fuel load (with its consequent structure weight penalty) which erodes a significant fraction of the HLFC potential.…”