Hideto Kawashima

Flowfield and Heat Transfer Characteristics of Cooling Channel Flows in a Methane-Cooled Thrust Chamber

In recent years, methane has attracted attention as a propellant for liquid rocket engines because of its various advantages compared to typical propellants such as hydrogen. When methane is used as a coolant for a regenerative cooling system, its near-critical thermodynamic and transport properties experience large variations because its critical pressure is higher than that of typical propellants; this significantly influences the flowfield and heat transfer characteristics. Therefore, adequate understanding of the flowfield and heat transfer characteristics of methane in regenerative cooling channels is a prerequisite for future engine development. In this study, conjugated coolant and heat transfer simulations were performed to investigate the flowfield and heat transfer characteristics of transcritical methane flows in a sub-scale methane-cooled thrust chamber. The computed results were validated against experimental data measured in hot firing tests. They compared well with the measured pressures and temperatures in cooling channels, and wall temperatures were within the permitted levels. Detailed flow analysis revealed peculiar flow structures in the cooling channel: a strong secondary flow induced in the concave-heated part in the channel throat section and the coexistence of two different gas phases—ideal and real—in a single cross-section in the cylindrical region. A high wall temperature appeared in the cylindrical region of the thrust chamber under the considered conditions; this was due to the heat transfer deterioration induced by an M-shaped velocity profile and a turbulent heat flux reduction.

Flowfield and Heat Transfer Characteristics of Cooling Channel Flows in a Subscale Thrust Chamber

Flowfield and heat transfer characteristics of supercritical parahydrogen flows in a cooling channl of a sub-scale hydrogen-cooled thrust chamber are investigated using Reynolds-Averaged Navier-Stokes simulation, in which conjugated heat transfer between coolant flow and chamber wall is taken into account directly. The considered system pressure ranges from 3.8 to 4.6 MPa, and temperature from 43 to 324 K at Reynolds number more than 1× 10 5 . The computed results are validated against the experimental data measured in the hot firing testings, which compare well with measured pressures and temperatures in a cooling channel, and wall temperature in a hot firing testings. Detailed flow structure and heat transfer characteristics in a cooling channel are clarified, showing strong thermal and density stratification, secondary flow effect, and particular asymmetric heat transfer characteristics.

Conjugated Combustion and Heat Transfer Modeling for Full-Scale Regeneratively Cooled Thrust Chambers

Regenerative cooling is still one of key technologies to develop high performance liquid rocket engines. To achieve high efficiency and reliability, understanding and accurate prediction of flowfield and heat transfer characteristics in regeneratively cooled thrust chambers are prerequisite. In the current study, a fully conjugated combustion and heat transfer simulation for full-scale regeneratively cooled thrust chambers was proposed and demonstrated for the LE-5B thrust chamber. In the proposed strategy, the injection and combustion processes in the hot-gas side, heat conduction in the chamber wall, and cooling channel flows are taken into account based on three-dimensional Reynolds-Averaged Navier-Stokes simulation. The computed results were validated against measured data from a hot firing test, showing reasonable agreement except for chamber outer wall temperatures. Detailed three-dimensional flow and thermal characteristics in the thrust chamber were clarified in the hot-gas side and the coolant side domains. Although the proposed numerical approach needs to be further improved quantitatively, it was confirmed that the present methodology is promising to understand and precisely predict flowfield and heat transfer characteristics in regeneratively cooled thrust chambers.

A Combustion Instability Phenomenon on a LOX/Methane Subscale combustor

JAXA is conducting LOX/methane rocket engine research and development. In this R&D activity, several series of fundamental tests have been carried out. Subscale combustor firing tests with single and multi-injector elements were conducted as a part of these fundamental test series, and combustion instabilities occurred in some tests of these test series. In this paper, the features of these instabilities, such as frequency characteristic, flame behavior, etc., are described. Although injection coupled instability was evaluated as the mechanism probably responsible for these instabilities, it was not able to explain some features of these instabilities. Therefore, Kelvin-Helmholtz instability will be evaluated in the future.

Flowfield and Heat Transfer Characteristics in the LE-X Expander Bleed Cycle Combustion Chamber

In Japan, a feasibility study of the new “LE-X” booster engine has been underway since 2005. One of the key technologies of the LE-X engine development is a regenerative cooling design to produce enough power to drive the turbopumps. The LE-X engine employs an elongated chamber design to pick up enough heat energy in the regenerative cooling channels. In the current study, a fully conjugated combustion and heat transfer simulation was performed to investigate the flow field and heat transfer characteristics for the regeneratively cooled combustion chamber of the LE-X engine. A three-dimensional Reynolds-averaged Navier–Stokes simulation was used to consider the injection and combustion processes of propellants on the hot-gas side, heat conduction in the chamber wall, and cooling channel flows. Details on the three-dimensional flow and thermal characteristics of the combustion chamber were clarified in the hot-gas and coolant side domains. In particular, significant thermal stratification was found to form in the radial direction of the cooling channel in the elongated cylindrical part of the chamber, which degraded the heat transfer and resulted in the highest wall temperature there.

Hot-gas-side Heat Transfer Characteristics of a Ribbed Combustor

For expander cycle liquid rocket engines, the enhancement of the heat transfer between combustion gas and regenerative coolant is one of the key issues. The adoption of a ribbed combustor is one possible method of enhancing heat transfer. Hot firing tests of sub-scale combustors with hot gas side wall ribs were conducted to evaluate enhancement of hot gas side wall heat extraction. Based on the firing test results, the influence of combustion pressure and mixture ratio on heat transfer enhancement was evaluated as the basic heat transfer characteristics with ribs and the scale effect was also examined. Nomenclature Pc = chamber pressure MR = mixture ratio ηC* = efficiency of characteristic exhaust velocity φ = rib efficiency

Verification of Prediction methods for Methane Heat Transfer Characteristics

Heat transfer of coolant methane in regenerative cooling chamber is one of the important characteristics. LOX/methane firing tests were conducted with a methane cooled combustor which had large number of measurement point in order to verify our prediction methods for coolant pressure loss and temperature gain in cooling channels. Two prediction methods were verified; a semi-empirical method and a numerical simulation method. A semiempirical method predicted coolant pressure and temperature properly, but wall temperatures around nozzle throat were predicted improperly. A numerical simulation method improved wall temperature prediction accuracy.

Status of Experimental Research on High Performance Methane-Fueled Rocket Thrust Chamber

For commercial vehicles, hydrogen and kerosene are widely used as fuel. Methane also has potential for use as a liquid rocket propellant. The authors have designed three types of injectors, which are to be evaluated with subscale hot-firing tests. Flow structure and combustion conditions are observed by single-element combustion visualization hot-firing test. By TDK analysis, nozzle efficiency can be increased by increasing combustion chamber pressure. Verification of analytical results by subscale hot-firing tests is also planned. Data obtained by both test campaigns will contribute to the advance of a high-performance methane engine design.