Experimental Method to Measure Pressure-coupled Responses of Induced Solid Rocket Instabilities Using a Next-generation Magnetic Flowmeter

Open Access
Herzog, Jan Rampada
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 20, 2012
Committee Members:
  • Michael Matthew Micci, Thesis Advisor
  • solid rocket instabilities
  • pressure-coupled response
  • magnetic flowmeter
The increased use and further development of high-energy-density propellants requires a method to quantitatively characterize the propellant’s stability. There are several methods, such as the T-burner, Rotating Valve Burner, and Impedance Tube that measure the acoustic admittance of the burning surface of solid propellant; however, each has its drawbacks. This study sought to improve techniques for measuring acoustic admittance using a magnetic flowmeter in a system that created a strong, uniform magnetic field, increased the number of velocity measurements taken in a single burn, and increased the amplitude of the forced pressure oscillation. Samples of a composite solid rocket propellant were burned inside a stainless steel combustion chamber. Acoustic oscillations were forced inside the chamber using two methods in an effort to impose an oscillating pressure on the burning propellant surface. The first method used a rotating toothed gear that passed over the exit area of a sonic nozzle. The second method took advantage of the deformation of a piezoelectric stack actuator to vibrate a titanium shim over the exit area. In both methods, the mean and oscillatory pressures were measured. Additionally, a permanent magnet and a flowmeter were utilized to measure the velocity of the combustion gases as they flowed from the burning surface. These measurements were then used to calculate the acoustic admittance of the burning propellant surface. A 0.5 0.06 Tesla magnetic field was successfully created inside the stainless steel combustion chamber by using eight N42-grade nickel-coated neodymium rare earth magnets. The magnetic field helped to increase the signal to noise ratio of the velocity measurement. A combustion chamber that allowed for eight velocity measurements was also successfully created. The use of eight velocity measurements in a single burn improved the statistical accuracy of each test. At the close of this investigation, the rotating toothed gear and piezoelectric actuator both failed in increasing the magnitude of the pressure modulation inside of the combustion chamber.