Roll Torque Induced By Star-perforated Motor Internal Flow
- Paper number
IAC-07-C4.2.07
- Author
Prof. Toru Shimada, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan
- Coauthor
Nobuhiro Sekino, IHI Aerospace Co, Ltd., Japan
- Year
2007
- Abstract
This paper describes our experiment and computation of roll torque caused by the internal flow of star-perforated solid rocket motor. The roll torque induced by motor internal flow is known from the early days but is not sufficiently understood among rocket scientists in academia and industry. In the background, there is complexity of a three-dimensional vortical flow in combustion chambers.
The roll torque occurring in the launch of the Mu-V rocket was reported by the author in the previous paper (Shimada, IAC-06-C4.3.02, Oct.2006), in which the relation with the internal three-dimensional flow was considered. The roll torque was observed in every seven launches during the early operation period of M-14 motor and it was one-order high compared with that of the aerodynamic and/or of thrust misalignment. The cause of the roll torque was discussed on the possibility of Type-I of Knauber’s classification, namely the combustion instability, but it was concluded that the possibility of Type-I was small because the mass efflux from the burning surface was relatively large in M-14 and at the same time, no strong sign of combustion instability existed.
In this paper, first, the result of a static firing test of a small motor (diameter of 500mm, burning period of 30 seconds, combustion pressure of about 5 MPa, the maximum thrust of about 50 kN, AP/HTPB/Al+MgAl propellant) is described. In this experiment, the swirling component of exhaust plume and the roll torque acting on the motor have been measured. The swirling flow is measured by the lift force acting on the vane which is installed right downstream the nozzle exit. The result shows the swirling has increased for several seconds after the ignition and attenuated gradually after that. On the other hand, roll torque has been evaluated from the balances of the force and the moment among the gravitational force, the suspension force from the test stand, and the two peripheral loads measured at diametrically either side (right and left) of the motor. The results show that the maximum torque has been about 28 N-m at around several seconds after the ignition in the opposite direction of the swirling flow. The evaluated dimensionless torque coefficient is rather a big value of 1.1×10 −3.
Next, discussion is made on whether the roll torque of M-14 is caused by Type-II, i.e., the internal swirling flow due to the grain shape. The M-14 has seven axial slots in each two grain segments. Because the mass efflux from the slots is larger than the remaining parts of the circumference of the cross section, a jet will flow out from each slot into the central port region. At least two possibilities can be considered; one is symmetric and the other is asymmetric secondary flow field in the cross section. It is only the symmetric case that no torque is generated; in which seven pairs of longitudinal vortices should steadily exist. On the other hand, if the symmetric flow is unstable, these jets might merge into one swirling flow which is supposed to be stabler than the symmetric flow. In this paper verification is sought concerning this supposition employing computational fluid dynamics simulations of the three-dimensional internal flow.
- Abstract document
- Manuscript document
IAC-07-C4.2.07.pdf (🔒 authorized access only).
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