Shock
Wave Boundary Layer Interaction
Abstract
Shock wave boundary layer
interaction is a common phenomenon that is experienced and observed in internal
flows. The performance of aerodynamics is influenced by the consequences of the
shock wave boundary layer interaction. The shock influences the velocity of an
aerofoil by subjecting the boundary to the pressure. In this report, various
properties of the pressure variable such as absolute pressure, relative
pressure and the coefficient of the pressure have been analyzed to determine
the effect on the velocity of an aerofoil.
The production of turbulence leads to inclined performance losses in the
performance of the aerofoil. Unsteady shock induced separation leads to loss of
performance and destruction of the structure of the aerofoil. The need to
achieve a balance between the Mac number, pressure, velocity, temperature,
Reynolds number, turbulence, angle of inclination among other variables that
influence the production of shock waves is the foundation upon which this
simulation report has been founded.
Introduction
Shock
wave boundary layer interaction are commonly observed in internal flows of high
speed especially in compressor blades, turbine cascades, nozzles fans, and
butterfly valves to mention but a few (Alshabu,
Olivier & Klioutchnikov, 2006).
Unsteady interactions of shock waves at the boundary layer has
detrimental results such as buffet flows which are aerodynamic instabilities,
shock induced oscillations (SIO) and high cycle fatigue failure (HCF) (Chen, Xu & Lu, 2010). A propensity and
need to achieve a balance between the consequences of the layer interactions
makes shock wave boundary layer interaction a valid topic of research.
Theoretical studies in the area indicate that shock wave layer boundary
interaction is a phenomena that is dependent on the Reynolds number (D'enos, Michelassi, Martelli, Arts & Paniagua,
2001). Many studies have revolved around transonic flow in an
oscillating airfoil. A study carried out by Tijdeman shows the interaction of
the unsteady and steady flow fields and the periodic motion of the shock. Cascade models are also known to be
self-excited due to transonic flow (Hasan,
Matsuo, Setoguchi & Sadrul Islam, 2012). Measuring various
parameters such as wake motions, static pressure and shock waves indicate that
self-excited nature of a shock oscillation is due to a closed loop mechanism. A
different proposition was made by Lee on a quantifiable feed-back mechanism of
the shock oscillation of a supercritical airfoil flow (Lee, 2001). The results of the experiment were an indication that
the time taken for a trailing disturbance to propagate from the shock to the
edge was equivalent to the time taken by an upstream movement of a wave from
the trailing end to the shock oscillation. The measurements were made at the
force spectra which was unsteady (Levy Jr, 1978).
The above hypothesis will be tested on a real time
simulation experiment that will enable comparison of results. Quantified amount
of research has been conducted on high speed aerodynamics. However, despite the
extensibility of this research, there still lacks a comprehensible
understanding of the flow characteristics of an airfoil in a channel. Providing
a theoretical approach to the study is not only limited but also not enough.
For this reason, this report is committed to providing a numerical analysis of
the results of simulation of how shock wave boundary formation are formed. This
is influenced via an ANSYS simulation in real time. A number of aerodynamics parameters such as the
angle, static pressure, pressure oscillation, and root mean square, and
frequency, coefficient of lift, drag, dynamic pressure and velocity are
examined.
Background of an Aerofoil
The
shape of an aerofoil has to be by convention prescribed according to the
surface and velocity distribution parameters. Depending on the type of flow,
various design models and mechanisms have been adopted for the inviscid flows (Levy Jr, 1978). For example, some are based on
the stream function that corresponds to the function of the aerofoil. According
to a report on how things work, the main requirement in functionality of an
aerofoil is to provide enough lift in an effort to counter the weight of the
plane (Menter, 1994). Viewing the
structure of an airplane, the lift and the weight are the two major forces that
interact and affect the movement and structure of the airfoil. The other
corresponding forces are the thrust and the drag forces. This can be properly
visualized in the structure of an airplane as presented in the figure below.
Geometrical structure of
the airfoil
The lift force is
generated using the wings. An airfoil refers to the cross-section shape of the
wings. Understanding the structure and properties of the airfoil is essential
and has been presented in the figure below.
When the pressure above
the wings is more than the pressure below, a lift force is generated. The
pressure difference between the below the wing position and above the wing
position results to an overall net force upwards
(Raghunathan, Gillan, Cooper, Mitchell & Cole, 1999). However, for this to be achieved, the
following factors has to be achieved. One, the surface of the wing has to be
curved or cambered and there must exist an angle of inclination that is tilted relative
to direction of the airflow.
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