True Dat my man, thats what you would really rather not put in front of you air pump, an obstruction, it will reduce efficiency.
S ducts also create air flow disturbances, in fact the reason Boeing and Sukhoi went for straight ducts has to do with efficiency and weight.
Highly integrated airframe-propulsion systems featuring ingestion of the airframe
boundary layer offer reduced noise, emissions, and fuel consumption. Embedded engine
systems are envisioned which require boundary layer ingesting (BLI) serpentine
inlets to provide the needed airflow to the engine.
These inlets produce distorted flow
profiles that can cause aeromechanical, stability, and performance changes in embedded
engines. Proper design of embedded engine systems requires understanding of the
underlying fluid dynamics that occur within serpentine inlets
Another facet of the study of flow in S-duct is flow control because these ducts find
practical application as aircraft air-intake ducts. The trend in modern fighter aircraft is to
have a short and highly curved S-shaped intake duct. The short length reduces the structural
weight of the aircraft and increases the internal space packaging efficiency. However, the
shortening of the duct results in a highly curved duct profile while still maintaining the
correct offset of the engine fan face (housed in the fuselage) and the intake entrance face (at
the exterior of the fuselage). Although the short intake duct is highly desirable for its
compactness and weight reduction, it is aerodynamically inefficient, as it is highly susceptible
to massive flow separation. In addition, the flow is coupled with bulk swirl with the presence
of stream-wise vortices.
These flow features lead to total pressure losses in the duct, flow
distortion at the duct exit and hence flow non-uniformity at the engine fan face.
while is possible to design an efficient S duct, straight ducts are prefered
The diffusing S-duct is a typical aircraft inlet geometry. It decelerates air entering the compressor and
increases the static pressure. The Lockheed Matin F-16 has a chin-type S-duct and Korean advanced
supersonic trainer T-50 has a bifurcated S-duct.
A well designed diffusing S-duct can help to enhance engine performance by delivering a nearly
uniform flow with a small transverse velocity component at the engine compressor entrance.
But the
centerline curvature associated with the S-duct makes a centrifugal force and cross-stream pressure
gradient between the bottom and the top of S-duct. As a result the diffusing S-duct integrates the
complex 3-dimensional internal flow which includes secondary flows and flow separation. Wellborn
et al. [1] performed a compressible subsonic flow experiment through a representative S-duct
configuration and investigated the complicated flow mechanism in detail. The baseline diffuser of our
design corresponds to the experimental configuration of Wellborn et al.
The aerodynamic performance of subsonic diffusers is principally determined by two
parameters; the flow distortion at the outlet of the diffuser and the total pressure recovery. If the flow
distortion is reduced and the total pressure recovery is close to one, it can be considered to be welldesigned.
функцию сверхманевренности (Lockheed Martin F/A-22 Raptor: Stealth Fighter. Jay Miller. В качестве недостатков известного самолета можно указать следующее: - невозможность управления в каналах крена и рысканья при полете на малых - скоростях, поскольку двигатели расположены вплотную друг к другу, что не not позволяет создать достаточный для управления момент - расположение двигателей вплотную друг к другу делает невозможным - расположение в фюзеляже грузовых отсеков;изогнутая форма каналов воздухозаборников требует увеличения их длины, и, - следовательно, массы самолета
feature super maneuverability (Lockheed Martin F/A-22 Raptor: Stealth Fighter. Jay Miller. 2005). In 2005).As a well-known disadvantages of the aircraft, you can specify the following: Inability to control the channels roll and yaw when flying at low speeds, because the engines are located close to each other, which does not allows you to create an adequate management time; The engines close to each other makes it impossible location in the fuselage cargo compartments; -
Curved air intake duct requires an increase in their length, and; hence, the mass of the aircraft
Both the commercial and the military aircrafts generally use the S-ducts to deliver the captured flow from far field to the engine compressor. The engine efficiency is influenced by the intake performance remarkably. Therefore, an efficient inlet duct should be able to deliver uniform and high pressure-recovery flow to the engine face. From the structural and aerodynamic point of view, it is more effective the length of inlet is short.
The short length of duct, however, needs high curvature of the duct and highly curved duct generates large separated flows.
S-duct air inlets are very commonly used on cruise missiles. In order to reduce the missile observability
and mass and to increase the volume of fuel tanks, their geometry is more and more constrained. Their design
is optimized for cruise flight conditions. During high-g maneuvers, external conditions and forebody interactions
can produce large separations leading to important pressure losses, high compressor face distortion,
with the risk of compressor instabilities
Aircraft performance strongly influences this selection as does the internal fuselage structure and available space, for example, inside the fuselage.
Aircraft stealth requirements seem to demand highly curved intake ducts that are prone to more or less heavy flow separations.
