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In this study, a new 1D solution algorithm named CAP_EJ was proposed to predict the performance of ejectors in high altitude wind tunnels. CAP_EJ combined the constant area mixing (CAM) and constant pressure mixing (CPM) ejector concepts, and assumed that the mixing of the primary and secondary flows occurs within a constant area mixing duct, with equal static pressures at the mixing point. Prediction results by CAP_EJ were consistent with existing studies, showing that the entrainment ratio was inversely proportional to the total pressure of the primary flow, and increased as the area ratio increased. Verification was performed through comparison with 2D numerical simulation and other 1D analysis methods, showing good agreement within 5 % deviation. However, when using CAP_EJ to analyze CAM ejectors, upper bounds on the area of the secondary flow need to be confirmed. [ABSTRACT FROM AUTHOR]

The effects of the flame temperature and the absorption coefficient on interactions between radiative heat transfer and the flame behavior were numerically investigated using high-fidelity numerical code with the discrete ordinates method. To study the effects of the flame temperature and the absorption coefficient, three different flame temperatures and four different absorption coefficient conditions were selected, so twelve test cases were studied in total. In the numerical test results, radiation effects resulted in preheating of the reactant gases and heat loss from the product gases. A higher flame temperature resulted in stronger preheating effects in reactants near the flame. Due to the preheating effects, with the appropriate absorption coefficient, the peak temperature appeared at the flame front. Lower flame temperatures resulted in larger reabsorption effects in the product zone. The peak temperature at the flame front and the flame speed were influenced by the combined effects of preheating and radiative heat loss at the flame front. Depending on the conditions, due to those effects, the peak temperature and the flame speed could increase or decrease. When the absorption coefficient was sufficiently large, the temperature decrease was reduced in the product zone. [ABSTRACT FROM AUTHOR]

To understand the initiating mechanism of low frequency instability (LFI) in hybrid rocket combustion, numerical calculation was performed using a direct numerical simulation (DNS). Special attention was paid to the effect of the equivalence ratio on the shift in the phase difference between pressure (p') and heat release oscillations (q'). A change in the equivalence ratio was considered by varying the temperature and composition of the combustion gas that entered into the post combustion chamber. In the obtained results, additional combustion was successfully simulated along with a vortex generation over the backward step, and combustion pressure and heat release oscillations were clearly reproduced as small vortices that move downward. In addition, the obtained results confirmed that the phase difference between pressure and heat release oscillations shifted because of the changes in the propagation speed of the pressure wave when the temperature of the combustion gas changes. [ABSTRACT FROM AUTHOR]

The ejector system is a useful device for creating high altitude conditions for ground tests of supersonic engines. The ejector performance can be immediately changed by varying the ejector operational mode. The ejector nozzle pressure ratio is well known to have a significant effect of the operational mode of an ejector. However, the effects of the mixing duct length and other geometric design parameters on the ejector mode change have not been clearly determined. In this study, the effects of ejector component geometries and inflow conditions on ejector operational mode are investigated by numerical analysis. By changing the inflow conditions and geometric parameters, twelve test cases are studied. Using the numerical test results, the flow pattern and suction pressure performance of the ejector with a fixed secondary mass flow rate are compared. In the numerical test results, a high primary nozzle stagnation pressure induces a highly underexpanded flow, resulting in the critical operational mode. For the critical operational mode, the mixing duct must be sufficiently long to accommodate the shock train and the choking zone. Primary nozzles with wide angles also induce widely expanded nozzle flows and result in the critical operational mode. [ABSTRACT FROM AUTHOR]

As a multiple-start ignition method for liquid-fuel rocket engines, the gas-dynamic igniter has many advantages, such as a simple configuration, low weight and high structural strength. However, because of the complexity of the flow of the working fluid, the details of the thermal processes involved are not clearly understood. In this study, the thermal and flow characteristics of a gas-dynamic igniter are investigated through numerical simulations using the software OpenFOAM. The simulation results show that the pressure within the igniter undergoes oscillations. The axial flow velocity decreases across the pressure wave front so that the kinetic energy of the flow is converted to thermal energy. The temperature increase within the oscillation tube of the igniter is strongly correlated with the entry mass flow. Therefore, the tube inlet area should be designed according to the igniter nozzle flow to achieve the best performance from a gasdynamic igniter. [ABSTRACT FROM AUTHOR]