Diffusers play a vital role in many fluid machines to convert kinetic energy into pressure energy. The field of application of diffusers is very wide and diffusers are used in gas turbines, pumps, fans, wind tunnels, water tunnels and many other fluid flow systems. This paper discusses the results of flow through straight conical diffusers of half-cone angles 5° and 7° with steady uniform velocity of flow and wake type distorted flow at inlet. The wake type distortion at inlet was produced by a streamlined body and a bluff body. A low speed wind tunnel was used for the experiments and the diffusers were fabricated from cast aluminium blocks. The mean velocity and the turbulence parameters were measured using a constant temperature hot-wire anemometer. © 2007 Elsevier Inc. All rights reserved.

Venkitachalam S. Ganesan

Fans

Flow of fluids

Gas turbines

Kinetic energy

Pumps

Turbulence

wakes

Wind tunnels

ALUMINIUM BLOCKS

Bluff body

Reynolds stresses

VELOCITY DISTORTIONS

Diffusers (fluid)

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Experimental Thermal and Fluid Science

In the present study, performance characteristics of a high altitude test facility for testing large area ratio rocket engines have been investigated. Steady-state numerical simulations have been performed initially to highlight the effects of operational parameters on a high altitude test facility operation. Later, the performance of the test facility during the startup phase of the rocket motor has been analyzed. The predicted results show that during the initial high altitude test facility evacuation, the desired vacuum level is attained when the primary jet flow attaches to the ejector duct walls smoothly, thereby arresting any back flow. However, at the fully started condition of the motor, the selfejector action of the rocket plume plays a major role in maintaining the desired vacuum condition and, hence, the ejector flow rate can be reduced significantly. The injection of water as a fine spray cools the hot gas to a sufficiently low temperature (∼600 K) prior to its release into the atmosphere. The transient predictions capture dynamic phenomena, such as the initial back flow of exhaust gas, and the attainment of self-ejection capability by rocket exhaust in the later stage. The predicted results compare well with in-house experimental data measured during cold and hot flow tests. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

AIAA Journal

Simulations of high altitude tests for large area ratio rocket motors

The performance of a second-throat ejector-diffuser system employed in high-altitude testing of large-area-ratio rocket motors is considered under various steady and transient operating conditions. When the diffuser attains started condition, supersonic flow fills the entire inlet section and a series of oblique shock cells occurring in the diffuser duct seal the vacuum environment of the test chamber against backflow. The most sensitive parameter that influences the stagnation pressure needed for diffuser starting is the second-throat diameter. Between the throat and exit diameters of the nozzle, there exists a second-throat diameter value that corresponds to the lowest stagnation pressure for starting. When large radial/axial gaps exist between the nozzle exit and diffuser duct, significant reverse flow occurs for the unstarted cases, which spoils the vacuum in the test chamber. However, the starting stagnation pressure value remains unaffected by the axial/radial gap. Numerical simulations establish that it is possible to arrive at an optimum diffuser geometry that facilitates early functioning of the high-altitude-test facility during motor ignition phase. The predicted axial variations of static pressure and temperature along the diffuser for the testing of a cryogenic upper-stage motor agree well with available experimental data. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

Journal of Propulsion and Power

Performance evaluation of second-throat diffuser for high-altitude-test facility

Experimental investigations of flow through conical diffusers with and without wake type velocity distortions at inlet

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering

Effect of inlet swirl on the performance of annular diffusers having the same equivalent cone angle

Experimental performance analysis of an annular diffuser with and without struts

Flow development and turbulence length scales within an annular gas turbine exhaust diffuser

Bluff-Body Wakes, Dynamics and Instabilities

Aspects of Bluff Body Wake Control

Journal	Experimental Thermal and Fluid Science
ISSN	08941777
Open Access	No