A peniche (or stand-off
) is material inserted between a half-model, often of an
airplane
An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spe ...
, and the wall of a
wind tunnel
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
. ''Péniche'' is a French nautical term meaning barge. The purpose of the peniche is to remove or reduce the influence of the
boundary layer on the half-model.
[Doerffer, Piotr and Oskar Szulc]
"High-lift behaviour of half-models at flight Reynolds numbers"
Task Quarterly Vol. 10, No. 2, pp. 191–206. 2006. The effect of the peniche itself in
fluid dynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...
is not fully understood.
Half-models are used in wind-tunnel testing in
aerodynamics
Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
, as larger scale half-models in constant pressure tunnels operate at increased
Reynolds number
In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be domi ...
s closer to those of real aircraft. One trade-off is the interaction between the central part of the half-model and the wall boundary layer.
Inserting a peniche between the centre line of the half-model and the wall of the wind tunnel attempts to eliminate or reduce that boundary layer effect by creating distance between the model and the wall. Varying widths and shapes of peniches have been used; a peniche that follows the longitudinal cross section contour of the half-model is the simplest.
The peniche itself affects the fluid dynamics around the half-model. It increases the local
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
on an inboard wing, while having no influence on an outboard wing.
[Melber-Wilkending, Stefan and Georg Wichmann]
"Project ForMEx — A New CFD Approach for Transposition of Wind Tunnel Data Towards Flight Conditions"
from New Results in Numerical and Experimental Fluid Mechanics VI. Cameron Tropea, Suad Jakirlic, Hans-Joachim Heinemann, Rolf Henke, Heinz Hönlinger eds. pp. 113-120. 2006. The blocking of the peniche in the flow field leads to further displacement of the flow, which in turn leads to higher flow speeds and local angles of attack.
How strong of an effect the peniche has is a function of the angle of attack, with the effect present at all angles.
References
{{reflist
Fluid dynamics