AFT Blog
The time was almost 30 years ago and it is fair to say I was not quite out of the "still wet behind the ears" stage for an engineer. I had been working in industry for about three years and I was just given a project that would change my career direction and, in fact, my life. The project? I was assigned to evaluate a new concept Pogo suppressor on a cryogenic rocket engine liquid oxygen (LOX) feedline.
How did I end up getting assigned this project? Well, I had a few things going for me at that stage of my career. Firstly was that my company division was on a massive hiring spree. Since I had been hired three years earlier my division had doubled in size. Fortuitously for me, that meant I was now in the upper 50% of seniority. Secondly, I had just had a performance review and I had casually told my immediate supervisor during the review that I would be interested in learning about waterhammer should the opportunity arise. Thirdly and finally, I had demonstrated a knack for solving tough analytical problems. What that meant is that I was in the enviable position of having my supervisors assign me to any problem that was out-of-the-ordinary and otherwise unusually difficult. The new Pogo suppressor was such a problem.
In case you have not noticed, rockets can be really loud. Sound suppression on vertically launched rockets (and the Space Shuttle, back when it was flying) is more important than most of you would think. And for a different reason than most of you would guess.
Every so often I get to talk about my first job which was in the aerospace industry where I first learned about sound suppression systems. Today AFT software is used on several of these systems by our customers in the aerospace industry as well as NASA.
The flowrate of water used in the sound suppression process is enormous. Which is why they are often called "deluge systems".
Hurricane Irma ravaged the Caribbean Islands and the state of Florida. Sixteen days prior, Hurricane Harvey ravaged the coastal area of Texas. Weather experts said this was the first time in recorded history that two Category 4 hurricanes made landfall in the United States in the same season. Each hurricane caused billions of dollars in damage and impacted millions of people.
Especially in Irma’s case, there was considerable discussion of the computer modeling used to predict the path and strength of the hurricane. As I have worked in computer modeling for most of my 30+ year career, this piqued my interest and I decided to educate myself a little more on the topic as it relates to hurricanes.
The first resource I pursued is one of our software developers here at AFT, John Lindsay. John has an undergraduate degree in Meteorology and a Master’s degree in Computer Science. John is a self-described weather geek who has a weather station at his home. We talked about weather modeling and he gave me some links to read further, which I did.
It was sometime around 1988 and it was pitch dark outside. I and some of my aerospace colleagues from work were driving in a car caravan from San Diego to Edwards Air Force Base at the ungodly hour of 3AM. The Space Shuttle Discovery was scheduled to land that morning and we wanted to see it.
From the moment I woke up in the middle of the night and all the way through the drive to Edwards AFB to the parking and walk to the viewing area to the standing in the cool, early morning air for a couple hours, I was questioning whether the whole effort was worth it. The landing of Discovery was not even certain. Weather conditions could postpone the whole thing.
And then someone pointed at the sky and yelled "There she is!". And I saw her too. Then a minute later we all heard the distinct double sonic boom. And I instantly knew it had been worth it.
Pulsation in fluid systems...Is it steady-state or is it transient? Well, it is both. Kind of. Pulsation causes periodic transients that are regular in nature and thus considered steady-state. It can be called "steady-state pulsation".
The problem is not whether pulsation is steady-state or transient. It is whether the frequencies that are excited by the pulsation are at or near the acoustic resonant frequencies of the fluid system. If so, there can be problems. API 674 defines the allowable pulsation limits for positive displacement pumps.
AFT will soon release the new PFA module for AFT Impulse. PFA stands for Pulsation Frequency Analysis. This new module will help engineers predict, understand and avoid resonant frequencies related to the fluid acoustics. It will also help engineers assess whether their system is in compliance with API 674.