Ignition Overpressure Research Articles

A study of barrier walls for mitigation of unintended releases of hydrogen

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. Depending on the leak diameter and source pressure, the resulting consequence distances can be unacceptably large. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. An experimental and modeling program has been performed at Sandia National Laboratories to better characterize the effectiveness of barrier walls to reduce hazards. This paper describes the experimental and modeling program and presents results obtained for various barrier configurations. The experimental measurements include flame deflection using standard and infrared video and high-speed movies (500 fps) to study initial flame propagation from the ignition source. Measurements of the ignition overpressure, wall deflection, radiative heat flux, and wall and gas temperature were also made at strategic locations. The modeling effort includes three-dimensional calculations of jet flame deflection by the barriers, computations of the thermal radiation field around barriers, predicted overpressure from ignition, and the computation of the concentration field from deflected unignited hydrogen releases. The various barrier designs are evaluated in terms of their mitigation effectiveness for the associated hazards present. The results show that barrier walls are effective at deflecting jet flames in a desired direction and can help attenuate the effects of ignition overpressure and flame radiative heat flux.

Evaluation of barrier walls for mitigation of unintended releases of hydrogen

Hydrogen jet flames resulting from ignition of unintended releases can be extensive in length and pose significant radiation and impingement hazards. Depending on the leak diameter and source pressure, the resulting consequence distances can be unacceptably large. One possible mitigation strategy to reduce exposure to jet flames is to incorporate barriers around hydrogen storage and delivery equipment. While reducing the extent of unacceptable consequences, the walls may introduce other hazards if not properly configured. An experimental and modeling program has been performed at Sandia National Laboratories to better characterize the effectiveness of barrier walls to reduce hazards. This paper describes the experimental and modeling program and presents results obtained for various barrier configurations. The experimental measurements include flame deflection using standard and infrared video and high-speed movies (500 fps) to study initial flame propagation from the ignition source. Measurements of the ignition overpressure, wall deflection, radiative heat flux, and wall and gas temperature were also made at strategic locations. The modeling effort includes three-dimensional calculations of jet flame deflection by the barriers, computations of the thermal radiation field around barriers, predicted overpressure from ignition, and the computation of the concentration field from deflected unignited hydrogen releases. The various barrier designs are evaluated in terms of their mitigation effectiveness for the associated hazards present. The results show that barrier walls are effective at deflecting jet flames in a desired direction and can help attenuate the effects of ignition overpressure and flame radiative heat flux.

A post‐flight ignition overpressure review for the Arex I‐X test rocket.

Ares I‐X post flight ignition overpressure review ignition overpressure (IOP) is an unsteady fluid flow and acoustic phenomena caused by the rapid expansion of gas from the rocket nozzle within a ducted launching space resulting in an initially higher overpressure wave. This wave is potentially dangerous to the structural integrity of the vehicle. An in‐depth look at the IOP environments resulting from the Ares I‐X solid rocket booster configuration showed good correlation between the pre‐flight predictions and post‐flight analysis results. Correlation between the chamber pressure and IOP transients showed successful acoustic mitigation, containing the strongest IOP waves below the mobile launch pad deck. The flight data allowed subsequent verification and validation of Ares I‐X unsteady fluid ducted launcher predictions, computational fluid dynamic models, and strong correlation to historical shuttle data.

Studies on Internal Flow Choking in Dual-Thrust Motors

Adetailed picture of the internal flow during the starting transient of high-performance solid rocket motors (SRMs) is of topical interest for several reasons in addition to the motor performance itself [1–12]. Despite the fact that many of the existing models could predict the internal flow features of certain classes of SRMs, none of these models could capture the unusual starting transient flow features such as pressure overshoot and pressure-rise rate often observed during the initial phase of operation of the dual-thrust motors (DTMs) [1]. Ikawa and Laspesa [8] reported that during the first launching of the space shuttle from the Eastern Test Range, the launch vehicle experienced the propagations of a strongly impulsive compression wave. This wave was induced by the SRM ignition and was emanating from the large SRM duct openings. The analysis further showed that the compression wave created by ignition of the main grain was the cause of the ignition overpressure on the launch pad [9]. Alestra et al. [10] reported that Ariene 5 launcher experienced overpressure load during the liftoff phase. The overpressure is composed of the ignition overpressure, which emanates from the launch pad, and the duct overpressure, which emanates from the launch ducts. Of late, Sanal Kumar et al. [1,2] reported that abnormal high-pressure overshoot in certain class of DTMs during the startup transient is due to the formation of shock waves because of the fluid-throat effect, which has received considerable attention in the scientific community. This manuscript is the continuation of the previous connected note for establishing the intrinsic flow physics pertinent to internal flow choking in inert simulators of dual-thrust motors [1]. Note that the illustration of ignition pressure spike is deliberately set aside in this note for explaining the intrinsic flow physics pertinent to internal flow choking without complications arising from the propellant combustion.

Study of the Ignition Overpressure Suppression Technique by Water Addition

The main objective of this study is to gain an understanding of the mechanisms responsible for the suppression of the ignition overpressure observed when water is injected through discrete nozzles into a rocket exhaust. A simplified launch-vehicle/launchpad configuration of relevant importance is selected for this study. This configuration is then numerically modeled using two-phase computational fluid dynamics with a representative motor startup sequence and a series of water addition configurations. The study focuses on the interaction between the ignition overpressure wave and the injected water. Chemical reactions are not included in the model; therefore, the effect of afterburning of fuel-rich exhaust is omitted in this study. A total of 11 water addition configurations were studied. The study demonstrated that ignition overpressure is strongly affected by the cooling of the plume and the amount of obstruction restricting the expansion of the plume. Also, the study suggests the existence of an optimal water addition rate with a weak dependence on the water nozzle pressure drop.

Space Shuttle Model acoustic/overpressure test results

The SSV's engine-generated acoustics and ignition overpressure environments have been long considered as severe dynamic inputs to a reusable aero-frame structure with a payload located in close proximity to the propulsion systems. The definition of these environments and the noise suppression techniques that are required for SSV launch have been provided from a dynamically scaled hot propulsion model. The scale factor is 6.4% of the Shuttle with the vehicle launch facility with exhaust deflector and duct geometry being simulated. Water injection into the hot exhausts is also scaled for sound suppression for both on-pad and liftoff cases. The environments measured on model are then scaled to provide launch vehicle environments for vehicle, launch facility, and farfield areas. Overpressure environments from SRB ignition are also acquired from over 100 measurements on the vehicle and launch facility. Suppression techniques are being investigated for Western Test Range (WTR) launchers and for thrust augmented configurations of the Shuttle.