Correct Answer : standing and travelling waves
Explanation : Tangential mode can be considered as two waves: Standing wave and traveling wave. Traveling wave is also called as spinning wave. Standing wave remains fixed in position while the traveling tangential wave has a rotation of the whole vibratory system.
Correct Answer : Option (A) : Pogo
Explanation : Pogo instability is a longitudinal instability due to propellant flow rate disturbances. They are low-frequency waves, usually lying in the 10-50 Hz frequency zone.
Correct Answer : Option (C) : Chugging
Explanation : Chugging can occur in test facilities due to the propellant pump cavitation. It can also happen due to gas entrapment in propellant flow or due to tank pressurization control fluctuations.
Correct Answer : Option (D) : squealing
Explanation : Squealing is the term used to denote combustion instabilities with high-frequency of occurrence of fairly large concentrations of vibratory energy. The frequency range lies above 1000 Hz. It is also called screaming.
