TITLE : COMPRESSIBLE FLOW 1.0 INTRODUCTION The aim of this experiment is to investigate compressible flow in a convergent-divergent nozzle. But before starting the experiment, a brief knowledge on this convergent-divergent nozzle should be introduce first so that students know what this experiment all about is. Converging-Diverging or "de Laval" Nozzles have been widely used over the last few decades in many engineering contexts, from civil and mechanical up to aerospace uses. It is a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass shape. They are designed to accelerate fluids to supersonic speeds at the nozzle exit. Because of this, the nozzle is widely used in some types of steam turbines and rocket engine nozzles. It also sees use in supersonic jet engines. Their operation relies on the different properties of gases flowing at subsonic and supersonic speeds. The speed of a subsonic flow of gas will increase if the pipe carrying it narrows because the mass flow rate is constant. The gas flow through a de Laval nozzle is isentropic (gas entropy is nearly constant). In a subsonic flow the gas is compressible, and sound will propagate through it. At the "throat", where the cross-sectional area is at its minimum, the gas velocity locally becomes sonic (Mach number = 1.0), a condition called choked flow. As the nozzle cross-sectional area increases, the gas begins to expand, and the gas flow increases to supersonic velocities, where a sound wave will not propagate backwards through the gas as viewed in the frame of reference of the nozzle (Mach number > 1.0). The purpose of this report is to gain an understanding of the nature of this flow by investigating the pressure ratios effects on the mass flow rate of air through the system and the differing pressure distributions that occur at varying lengths into the nozzle.
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TITLE : COMPRESSIBLE FLOW
1.0 INTRODUCTION
The aim of this experiment is to investigate compressible flow in a convergent-divergent
nozzle. But before starting the experiment, a brief knowledge on this convergent-divergent
nozzle should be introduce first so that students know what this experiment all about is.
Converging-Diverging or "de Laval" Nozzles have been widely used over the last few
decades in many engineering contexts, from civil and mechanical up to aerospace uses. It is
a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass
shape. They are designed to accelerate fluids to supersonic speeds at the nozzle exit.
Because of this, the nozzle is widely used in some types of steam turbines and rocket engine
nozzles. It also sees use in supersonic jet engines.
Their operation relies on the different properties of gases flowing at subsonic and
supersonic speeds. The speed of a subsonic flow of gas will increase if the pipe carrying it
narrows because the mass flow rate is constant. The gas flow through a de Laval nozzle is
isentropic (gas entropy is nearly constant). In a subsonic flow the gas is compressible, and
sound will propagate through it. At the "throat", where the cross-sectional area is at its
minimum, the gas velocity locally becomes sonic (Mach number = 1.0), a condition called
choked flow. As the nozzle cross-sectional area increases, the gas begins to expand, and the
gas flow increases to supersonic velocities, where a sound wave will not propagate backwards
through the gas as viewed in the frame of reference of the nozzle (Mach number > 1.0).
The purpose of this report is to gain an understanding of the nature of this flow by
investigating the pressure ratios effects on the mass flow rate of air through the system and
the differing pressure distributions that occur at varying lengths into the nozzle.
1.1 OBJECTIVES
i. To study about the characteristics of pressure-flow rate of convergence-divergence
tube
ii. To demonstrate the phenomenon of choking.
1.2 THEORY
Figure 1. Covergent-Divergent duct
Referring to the figure above, the steady energy equation between 0 and 2 is given by: