An Innovative Method of Investigating the Role of Turbulence in the Velocity Coupling Phenomenon

Abstract

An investigation has been conducted of the velocity coupling phenomenon reported in acoustically unstable solid propellant rocket motors. An innovative simulation facility has been built using solid carbon dioxide as the simulated propellant. The use of dry ice allows us to focus directly on the fluid mechanical aspect of the problem. Dry ice is contained in a two-meter long chamber. The acoustic disturbance in the chamber is introduced by means of a mechanically driven piston. Mass flow rate and acoustic pressure measurements indicate the existence of a coupling mechanism, other than pressure coupling, between the acoustic disturbance and dry ice sublimation process. Flow visualization using a high speed camera shows a high degree of mixing, near resonance, within the flow above the dry ice surface. The flow over the dry ice is very chaotic, probably turbulent. Hot film anemometry measurements show a broad-band spectrum at low frequencies with strong peaks at the driving frequency and its harmonics near resonance. A broad band spectrum is generally taken as an indication of turbulent flow. Acoustically induced turbulent forced convection is believed to be responsible for the increase in the sublimation rate of the dry ice (simulated burning of the propellant). We believe that turbulence is one of the principal mechanisms in the velocity coupling phenomenon.

Moderate‐to‐large injection and suction driven channel flows with expanding or contracting walls

“…It also improves our ability to capture the ablating surface during transpiration cooling of re-entry vehicles and solid rocket boosters [39]. It is equally useful in simulating the sublimation process of a solidified gas that is often used to mimic the regression of a solid propellant [40][41][42]. Although idealized rocket motors possess circular cross-sections, the channel flow geometry associated with a slab rocket motor has become no less popular in recent years.…”

The oscillatory channel flow with arbitrary wall injection

“…The source of harmonic waves can be external, user-defined, or internal, decreed by the channel's natural frequency. An example of the former type has been achieved in long rectangular channels by Ma et al [23], [24], and Barron et al [25]. These were motivated by the need to simulate the burning process of solid propellant grains in a hazard-free environment.…”

A Novel Investigation of the Oscillatory Field Over a Transpiring Surface

“…Our experimental "ndings seem to be in good agreement with the theory. 6. CONCLUSIONS Several experimental de"ciencies of previous investigations were improved in this experiment.…”