One main physical feature of hybrid rocket combustion is its diffusion flame structure that requires excessively long solid grain port which often leads to undesirable large slenderness of a rocket configuration. The diffusion flame also results in generally low combustion efficiency of hybrid rockets. Some remedial designs have used liquefying solid grain, such as paraffin, or mixing enhancement mechanisms to boost the overall combustion efficiency. Thus, shortened combustion chamber can be used to deliver reasonable thrust performance of hybrid rockets. In addition to the study of multi-stage mixing enhancer effects, a compact hybrid rocket motor design concept is also proposed in the present study to provide better form factors for hybrid rocket engine designs. This design concept features in vertical-flow structures such that greatly improved combustion efficiency is obtained. A 3D computational model with finite-rate chemistry and radiative heat transfer capabilities is employed to assess the mixing effectiveness and combustion efficiency of the new design concept. The present computational model is validated for a wide range of rocket propulsion design problems, including a single-port hybrid rocket motor with and without using a mixing enhancement mechanism. The internal ballistics and flame structures in the hybrid rocket engine with mixing enhancement designs are analyzed. Nomenclature C 1 ,C 2 ,C 3 ,C = turbulence modeling constants, 1.15, 1.9, 0.25, and 0.09. C p = heat capacity D = diffusivity F yz, F y, F z = integrated force, and component forces in the lateral direction Joint Propulsion Conferences 2 H = total enthalpy K = thermal conductivity or stiffness k = turbulent kinetic energy Q = heat flux T = temperature t = time, sec u = mean velocities V 2 = u 2 x = Cartesian coordinates or nondimensional distance = species mass fraction = turbulent kinetic energy dissipation rate μ = viscosity μ t = turbulent eddy viscosity (=C k 2 /) Π = turbulent kinetic energy production ρ = density = turbulence modeling constants, 0.9, 0.9, 0.89, and 1.15 for Eqs. (2), (4-6). τ = shear stress ω = chemical species production rate or natural frequency Subscripts r = radiation t = turbulent flow
Recently, the hybrid rocket propulsion has become attractive to the research community and has developed the trend to become an alternative to the conventional liquid and solid rockets. Among available hybrid systems, the N 2 O (Nitrous Oxide)-HTPB (Hydroxyl-Terminated PolyButadiene) hybrid propulsion represents the simplest but sufficiently efficient design. To date, research in developing hybrid N 2 O-HTPB propulsion system, despite some available fuel regression rate correlations, still strongly depends on experimental trials-and-errors, which are time-consuming and expensive. Thus, detailed understanding of the fundamental combustion processes that are involved in the N 2 O-HTPB propulsion system can greatly impact the research community in this field. This may further facilitate the successful modeling of the combustion processes and help improving the design of N 2 O-HTPB propulsion system in the future. A comprehensive numerical model with real-fluid properties and finite-rate chemistry is developed in this research to predict the combustion flowfield inside a N 2 O-HTPB hybrid rocket system. The effects of a mixing enhancer design are demonstrated experimentally and numerically in boosting the overall thrust performance of a hybrid rocket motor. Good numerical predictions as compared to experimental performance data are presented. Computation of the N 2 O flow rate control with a ball valve shows smooth variation behavior which is desirable in propulsion system designs. NomenclatureC 1 ,C 2 ,C 3 ,C µ = turbulence modeling constants, 1.15, 1.9, 0.25, and 0.09. C p = heat capacity D = diffusivity H = total enthalpy K = thermal conductivity k = turbulent kinetic energy L/S = ratio of long-axis to short-axis Q = heat flux T = temperature t = time, s u = mean velocities V 2 = ∑ u 2 x = Cartesian coordinates or nondimensional distance α = species mass fraction ε = turbulent kinetic energy dissipation rate θ = energy dissipation contribution µ = viscosity µ t = turbulent eddy viscosity (=ρC µ k 2 /ε) Π = turbulent kinetic energy production ρ = density σ = turbulence modeling constants, 0.9, 0.9, 0.89, and 1.15 for Eqs.(2), (4), (5), (6). τ = shear stress ω = chemical species production rate
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