Gallery of Results

In this page, we present a few results from our group's research on high speed flows, flow acoustics, and applications of aeroacoustic devices. References to published literature are also given for the interested reader.
Dr. Abhijit Dhamanekar's work on impingement jet noise 

Abhijit showed interesting results on the effect of surface roughness on the noise emanating from impinging jets.  As can be seen from the following sample results from his article in Physics of Fluids, 2014, impingement noise is suppressed with the use of rough plates. 

In a further study on the noise from jets impinging on permeable plates, Abhijit was able to find substantial quietening of impingement noise using permeable plates. These effects are due to fundamental modifications in the flow instabilities brought about by the porosity of the plates. The movies in this link demonstrate this strategy.

 Transonic resonance in jets
Dr. Jothi (INSA Visiting Fellow, Summer 2012) investigated transonic resonant tones in orifice and pipe jets. This study showed that under transonic flow conditions, tones significantly different from screech tones are emitted. (IJA).

Thermoacoustic refrigerator
The recent B.Tech project work of G. Chandrashekhar and G. Puneeth demonstrated thermoacoustic
cooling of more than 10 K (seen in thermal image below). Their work was a continuation of B.Tech
project of K. Sampath and M. Srikant

Twin-jet interactions
Note the fused shock-cells at small spacing (s/h = 0.5) for Ed-Ed configuration at a pressure ratio of 7.

Supersonic Free Jet Flows
Characteristics of a jet depends on its initial conditions. Notice below, the difference in the shock-structures between jets from an orifice and a pipe (See Paper)
In pipe jets, the pipe length greatly influences the spectral quality of noise emitted. This is because the jet evolution depends on its initial conditions including boundary layer thickness at the nozzle/pipe exit (Initial shear layer thickness). Notice that tones gradually vanish as pipe length increases. (Ref).
Similar effects using surface roughness is discussed in this paper.
A Hartmann whistle is a sound production device in which a high speed jet impinges on a cylindrical cavity closed at one end. The device emits intense tones, and controlled by the cavity length, spacing between the jet and cavity, stagnation pressure of air jet, etc.
Internal Chamfer of Hartmann whistle enhances sound emission at almost all angles (See Paper)

Thermal Effects in Resonant devices (whistles) 
Hartmann whistle also generates intense heat inside the cavity.
See below that the wooden cavity starts burning due to the heating
See Results of Narayanan's research below (work unpublished)  
Smrutimaya Pattanaik's research demonstrates heating even in
metallic cavities (results to be uploaded soon)...


 The sound from a Hartmann whistle can also be used to alter the shape of
liquid droplets and sprays. See pictures below:
Active  Control of Droplets and Sprays
 (paper to appear in IJSCD)

 Use of Sound for Measurement
Sound can also be used for measurement of temperature of hot zones and flames
(Temperature measurement in a hot-zone)
(Temperature measurement in a flame by assuming a temperature profile)