Hello

Which is the difference between Thrust Oscilation and the Pogo effect?
thnks

"Xabier" <fp@pf.es> wrote in message news:funr2m$tm0$1@aioe.org...
Hello

Which is the difference between Thrust Oscilation and the Pogo effect?
thnks

"POGO is a closed-loop oscillation involving longitudinal
i structural vibrations and pressure oscillations within the
liquid rocket propulsion system. The theory of such oscillations
is now well understood and are probably best described
by Rubin."

The above definition is found in the introduction of the following paper:

VOL. 7, NO. 12, DECEMBER 1970 J. SPACECRAFT 1407
Simulation of Saturn V S-II Stage Propellant Feedline Dynamics
R. S. RYAN,* L. A. KIEFLING^ AND H. J. BUCHANANJ
NASA Marshall Space Flight Center, Huntsville, Ala.
AND
W. A. JARVINEN
Northrop Corporation, Huntsville, Ala.
Oscillations involving the propellant feedlines, engines,
and longitudinal structural modes of the Saturn V S-II
stage are investigated, using an electronic analog computer.
The methods used to develop mathematical models and some
problems encountered are described. The effect of a nonlinear
gas bubble (cavitation) at the pump inlet is studied. The
simulation was able to match several characteristics of the
flight, including stability variations with NPSH, amplitude
sensitivity, and nonlinear waveforms. The cause of the limit
cycle which occurred on two flights was not found. The need
exists for accurate and complete test data, especially for
structural damping and local and engine dynamics.

So, the classic definition of POGO only involves liquid fueled rocket
engines.

Here is an abstract talking about solid rocket motors.

Instabilities and pressure oscillations in solid rocket
motors*1
Yves Fabignon, , a, Jöel Dupaysa, Gérard Avalona, Francois
Vuillotb, Nicolas Lupoglazoffb, Grégoire Casalisc and Michel
Prévostc a Office National d'Etudes et de Recherches
Aérospatiales (ONERA), Fundamental&Applied Energetics
Department, 29 Avenue de la Division Leclerc, F-92322,
Châtillon Cedex, France b Office National d'Etudes et de
Recherches Aérospatiales (ONERA), CFD&Aeroacoustics Department,
29 Avenue de la Division Leclerc, F-92322, Châtillon Cedex,
France c Office National d'Etudes et de Recherches
Aérospatiales (ONERA), Aerodynamics&Energetics Modeling
Department, 29 Avenue de la Division Leclerc, F-92322,
Châtillon Cedex, France

Abstract
The purpose of this paper is to give an overview of the main
results obtained on instabilities and pressure oscillations
in segmented solid rocket motors. A major part of this work
was carried out in the framework of the ASSM and POP R&T
programs supported by the French national space agency CNES
during the last decade. ASSM is related to Aerodynamics of
Segmented Solid Motors and POP for Pressure Oscillations
Program for the Ariane 5 solid booster (P230). Due to the use
of segmented technology for the P230 motor and the possible
acoustic oscillations inside the motor chamber, anticipated
at the beginning of the programs and confirmed later on static
firing tests, the main scientific objective of the ASSM program
was oriented towards the comprehension and the modeling of the
vortex shedding phenomena that are supposed to be responsible
of the pressure and thrust oscillations observed in the P230.
POP program was started in order to obtain an experimental and
numerical data base using subscale tests of 1/15th of the P230.
After the description of the instabilities observed in the P230
solid rocket booster, the scientific approach of the ASSM
program is detailed insisting on the validation of numerical
tools in order to predict oscillation frequencies and amplitudes.
The logic of work regarding POP program is also presented. The
main section of this paper provides an overview of different
results obtained in ASSM and POP programs to understand the
mechanisms driving to the instabilities in solid rocket chamber.
The most important recent result, inside ASSM and POP programs,
was the discovery of the parietal vortex shedding and the role
of aluminum combustion on instabilities. Together, these two
mechanisms seem to be an important potential source of
instabilities and provide a new vision of the P230 stability.

So there you go. Not terribly easy to sort through, but it's pretty clear
that the mechanisms which create POGO are different than the mechanisms
that create thrust oscillations in solid rocket boosters.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein