Thrust-optimized Nozzle Research Articles

Comparative study on the performance of turbulence models in flow separation of large expansion ratio nozzle

The asymmetry of flow separation inside the nozzle with large expansion ratio is the main factor for the generation of side-load in the engine, so the accurate prediction of the flow separation is of great significance. The turbulence model is the key to the prediction, but in different scenarios, the performance of the turbulence model can introduce huge uncertainties. In this paper, a typical thrust-optimized nozzle (VOLVO-S1) is simulated and analyzed for three widely used turbulence models: SST k - ω 、 RNG k - ε and Spalart-Allmaras model. The results show that all these models can effectively predict the mode of shock separation phenomenon. The comprehensive performance of SST k - ω is the best; The Spalart-Allmaras model has better prediction performance under low pressure ratio, and the RNG k - ε model has better prediction effect under high pressure ratio.

Design of Thrust-Optimized Scramjet Nozzle and Its Concise Estimation Method

This Paper is a computational investigation of a scramjet nozzle design based on maximum thrust theory and its feasibility analysis. A new design method for a two-dimensional complete thrust-optimized single expansion ramp nozzle under aerodynamic constraints by applying the method of characteristics is proposed. The carefully chosen verification and validation benchmarks confirm the accuracy, effectiveness, and superiority of the current method. Results indicate that the introduced design method has comprehensive advantages over the traditional approach under design/off-design conditions. Specifically, the maximum increase in axial thrust reaches 6.38%, and the maximum increase in lift exceeds 180%. Necessary conditions of the thrust-optimized nozzle design are deduced combining Prandtl–Meyer relation and corner conditions, which provides a direct judgment criterion for the rationality of initial design conditions, and leads to a concise dimension estimation method. Relative errors of no more than 5% demonstrate the credibility of this approach through a comparison with the theoretical solutions. The refined structure topology of the thrust-optimized single expansion ramp nozzle further reveals the equivalent relations between the aerodynamic and geometric design conditions based on the estimation results.

Numerical performance investigation of a thrust-optimized nozzle at different altitudes

One of the major design aspects of jet propulsion engines is the nozzle design. The value of thrust generated by the nozzle is dependent on both the nozzle design and the flight altitude. The present paper is intended to shed more light on the jet flow structure and its evolution with flight altitude. In addition, the variation of thrust generated by the nozzle with flight altitude is addressed. A well-defined nozzle profile is adopted as a case study and numerical simulation using a commercial CFD tool is conducted. The solution method is validated by reproducing the experiments conducted on the case study nozzle.

Appearance of Restricted Shock Separation in Rocket Nozzles

Uncontrolled flow separation in nozzles of rocket engines is not desired because it can lead to dangerous lateral forces. Different origins for side loads were identified in the past. Meanwhile, it is proven that in thrust-optimized or parabolic nozzles, a major side load occurs as a result of the transition of separation pattern from free shock separation to restricted shock separation and vice versa. Reasons for the transition between the separation patterns are discussed, and the cap-shock pattern, which is identified to be the cause of this transition, is closely analyzed. It turns out that this pattern can be interpreted as an inverse Mach reflection of the internal shock at the nozzle axis. To prove the transition effect as main side-load driver, a subscale test campaign has been performed. Two different nozzle contours, a thrust-optimized and a truncated ideal nozzle with equal performance data, were tested. Highest side loads were measured in the thrust-optimized nozzle, when the separation pattern changes from free to restricted shock separation. Side loads measured in the truncated ideal nozzle were only about one-third as high as in the thrust-optimized nozzle.