www.pulse-jets.com

Hello everyone its been a long time, How are you all??? Hope everybody is fine.

I would like to share some CFD simulated pulsejet engines which are quite interesting to understand the underlying physics. I will share some plot images and videos here for your reference.

Currently I am using CFD to develop new valveless pulsejet design,

https://youtu.be/pwA2IQGRzYc

Hey Ganesh, I too have not been around much, but think i should. Hope all is well with you too. Looks like fun.
You might try low pressure ambient at the tail if your start condition is high at the intake. All these years, and the one thing i still want to show on a running motor is the alternating nature of intake and exhaust pulses.
We'd always look at the sound file and say "wow, the second mode is REALLY STRONG!" I think i can see it in this video.

Mike Everman wrote:Hey Ganesh, I too have not been around much, but think i should. Hope all is well with you too. Looks like fun.
You might try low pressure ambient at the tail if your start condition is high at the intake. All these years, and the one thing i still want to show on a running motor is the alternating nature of intake and exhaust pulses.
We'd always look at the sound file and say "wow, the second mode is REALLY STRONG!" I think i can see it in this video.

Yes I am good and everything is smooth now. Hope everything is fine from your side.

Low pressure at outlet seems good initial condition, I will surely try it in my next simulation. The original initial condition that i gave is velocity of 10m/s all over the domain. The reason to give this was to mimic the blower air velocity inside pulsejet which we usually do in real time.

Now I am actually trying to perform Aero-acoustic analysis to visualize the pressure pulses inside and outside PJ. I thought this might give us an idea of the sound frequency at outlet. One important update, some people told me that we can even export the simulated pressure pulses to audio format and hear it live . Really excited to move on to acoustic analysis. Once it is done I will surely update it here in forum.

Thanks for following my post.

Regards
Ganesh

Aeroacoustics simulation using FW-H model. Listen to the sound file generated by placing the receiver inside the outlet tube.

Second try: Planning to create a far field and place the receiver 2m away from exhaust tube.

Regards
Ganesh

There are totally three sound files
Mic1- Sound received from impermeable surface (Wall)
Mic2- Sound received from 1feet distance away from outlet
Mic3- Sound received when mic placed above pulsejet

This took a while for me but its interesting. Please provide your suggestions.

Regards
Ganesh

Hi Ganesh, sounds like a pulsejet! A mic at the intake and exhaust would be interesting to see compared. I am particularly interested in the phase offset, is it 180 or 90? My knee-jerk is 180, but... It will tell us something about the average speed of sound in the duct.
I would like to set up a motor with daq and verify your predictions.
We'd (you'd) need to model a motor I have, though. One of my pocket jet scale ups would be ideal. With straight pipe exhausts, the next logical step would be adding ejectors and optimizing those.

Mike Everman wrote:Hi Ganesh, sounds like a pulsejet! A mic at the intake and exhaust would be interesting to see compared. I am particularly interested in the phase offset, is it 180 or 90? My knee-jerk is 180, but... It will tell us something about the average speed of sound in the duct.
I would like to set up a motor with daq and verify your predictions.
We'd (you'd) need to model a motor I have, though. One of my pocket jet scale ups would be ideal. With straight pipe exhausts, the next logical step would be adding ejectors and optimizing those.

I am ready to take up this project sounds interesting. This will also be a good reference for me (Validation ). You can share the dimensions of the engine and I will model it in CFD.

Regards
Ganesh

Great, I'll dig it up today. What is your time zone?

Mike Everman wrote:Great, I'll dig it up today. What is your time zone?

My time zone is

India Time Zone
UTC+05:30

Regards
Ganesh

Then good night!

This engine was made by me like 6 years back. Now I have simulated in CFD. Please follow below link for the video.

https://youtu.be/UXtoUmitbqE

That one sure looks like the exhaust and intake are in synch after it settles in. Maybe a little bit off. I didn't realize you could fold the geometry. That's cool. Ive always thought that a u-shape motor would be more energetic if the exits were alternating, where one make a higher pressure ambient for the other, just as it wants to draw air in, and vice-versa.

So then a new parameter crops up that may be important, that of the distance between exits and the speed of sound in ambient air between, on which this constructive interference depends.

Faaaaaascinating!

Yes backward inlet type is also possible in CFD. Here is another CFD simulation of a thermojet engine with 4 inlets. Please follow below link to the video,

https://youtu.be/NpSC3MzdiP4

Numerical simulation of valveless thermojet in commercially available software.

Combustion chamber pressure: 1.3bar
Peak temp: 2200K
Thrust: 4.2pounds approx 1.95kg

Video: https://youtu.be/1l-MQX_ozCk

Oh, that one is fun to watch! I would love to see the pressure animation as well. Does it not make sense that the velocity scale should be -300 to +300m/sec? Loses that "hot-cold" spectrum, but freezing it would allow some better interpretation.