Analyzing the impact of nitrogen ejection on suppression of rocket base heating

doi:10.1016/j.ast.2020.106275

Aerospace Science and Technology

Volume 107, December 2020, 106275

https://doi.org/10.1016/j.ast.2020.106275 Get rights and content

Abstract

Due to the reverse flow and recirculation caused by plumes, the base plate and nozzle external walls of a rocket suffer from severe base heating during its ascent. To protect the internal instruments from the base heating, nitrogen ejection, an active thermal protection, was adopted. The nitrogen with different total pressures and total temperatures is ejected from a tube in the base plate center to the base flow region, and its impact on the wall heat flux of the base plate and nozzle external walls is further investigated numerically. The impact of the total pressure as well as the total temperature of nitrogen ejection was analyzed numerically by computational fluid dynamics on the wall heat flux on the base plate and nozzle external walls. A density-based solver was used to solve the Reynolds-Averaged Navier-Stokes equations, and the Shear Stress Transport model was adopted to model turbulence. The results showed that nitrogen ejection can significantly reduce the rocket base heating by suppressing the reverse flow, and the base plate benefits more than nozzle external walls. As is expected, excessive total temperature increases wall heat flux. However, it is interestingly found that the wall heat flux could not decrease monotonically as the total pressure of the ejected nitrogen increases. Exceedingly large total pressure even exacerbates base heating. Therefore, it is crucial to restrict total pressure and total temperature in nitrogen ejection design. In the best case investigated, the maximum wall heat flux on the base plate and nozzle external walls was reduced respectively to 12.3% and 21.5%, and the average heat flux was reduced to 17.8% and 26.8%.

Introduction

When a rocket is ascending, the base heating on its base plate and nozzle walls may deteriorate the operation of other devices and further lead to launch failures, which could date from the Saturn launch vehicles [1]. In order to protect the instruments inside the rocket, the engineers put many efforts in the design of thermal protections on the base plate. However, underpredictions on base heat flux usually leads to redundant passive thermal protections, which decreases the payload efficiency. It was found that the base heating mainly results from the reverse flow after plume collision, which impinges on the base plate [2]. To suppress the reverse flow so as to reduce the heat flux on the base wall, Musial [3] proposed to eject nitrogen actively from the base center and investigated the flow field as well as the heat flux on the base plate experimentally. The results indicated an efficient decrease of the maximum heat flux on the base plate and better efficiency of the active nitrogen ejection than the passive thermal protection.

However, wind tunnel tests are too expensive to conduct, the flow field data is hard to be acquired non-intrusively, and the scale of the test model is complicated. Therefore, recently the computational fluid dynamics (CFD) has been extensively employed to analyze the base flow of a rocket. Mattias [4] used the low Reynolds number $k - ε$ model to predict the base flow of a single-nozzle and a four-nozzle blunt-rocket shaped vehicles. The results indicated that for single-nozzle configuration the recirculation transports the hot gas from the expanding plume to the base, and the multiple plumes for the four-nozzle configuration interact forming a reverse flow, which then impinges upon the base. Webster [5] employed a compressible Navier-Stokes flow solver, utilizing the Baldwin-Lomax mixing-length turbulence model, to simulate the base flow induced by exhaust plume impingement. The results seemed to be reasonable but further turbulence models remain to be tried. S.J. Zhang, J. Liu and X. Zhao [6] developed an integrated CFD tool for launch vehicle base heating analysis, where turbulence, chemical reactions and radiation were involved and high order data reconstruction scheme was adopted. The test case on the sub-scale X-33 vehicle validated this CFD tool in base heating predictions. R. Nallasamy and M. Kandula et al. [7] utilized the CFD code OVERFLOW to compute the base flow of a four-nozzle rocket in Musial's [3] wind tunnel tests, using the Baldwin-Barth one-equation turbulence model. Despite qualitative agreement, the numerical heat flux and pressure deviated quantitatively from Musial's wind tunnel test data [3] and the false secondary peak in heat flux was observed. The inaccuracy was believed to originate from the ideal gas assumption, the inaccurate turbulence model, the indefinite wall temperature and lack of grid refinement. Hideyo [8] used the commercial code Fluent to simulate the base heating of the H-IIA rocket based on the realizable $k - ε$ turbulence model. Although this simulation well estimated the general heating level, the computed total heat flux substantially deviated from the flight test. To find best practices for CFD simulations of launch vehicle ascent with plumes, Gusman et al. [9] compared the influences of the solver, the gas model, the viscous wall spacing, nozzle boundary condition approaches and the turbulence model on Saturn V. The results showed that the SST model [10], [11] exhibited superior performance to the Spalart-Allmaras model [12] in predicting Plume Induced Flow Separation (PIFS), and the flow distribution at nozzles' exits was of great significance. For sensitivity analysis, Mehta et al. [13] adopted Menter's Baseline (BSL) turbulence model to investigate the numerical sensitivity of base heating predictions, also based on Musial's tests [3]. Results showed that the BSL model [10], [11] performed well in predicting the heat flux on the base plate. Also, it was mentioned that the SST model [10], [11] performed equally well compared to BSL in base heating predictions. Moreover, BSL was also adopted by Petal [14] to estimate the base heating environment of Antares, which also manifested good agreement with the flight test data. Zhou et al. [15] investigated the base heating of a single-nozzle rocket and a four-nozzle rocket numerically, and performed flight experiments for the single-nozzle rocket. The results of the four-nozzle rocket base heating was validated by the wind tunnel test of Musial [3], and the calculated wall heat flux agreed well with the measurements. It was indicated that the convective heat flux increases before decreases as the rocket ascends. It is shown that CFD has become a powerful tool for rocket engineering analysis [16], [17], [18], and it is appropriate for analyzing the issue of rocket base flow and heating.

As far as we know, most of literature has focused on simulating base flow or predicting wall heat flux, but few detailed computation and analysis has been performed on the effect of gas ejection on reducing base heat flux up to now, which limits its further application in rocket thermal protection. Furthermore, although Musial [3] justified nitrogen ejection in reducing the heat flux on the base plate, the factors that could influence the suppression effectiveness lack analysis in detail, which limited further optimization of thermal protection design. Therefore the present work adopts the four-nozzle rocket model in our previous work [19], a configuration of Musial's wind tunnel tests [3], and adds a tube in the rocket base center to eject nitrogen. A commercial CFD software has been used and cases with different total pressures and total temperatures of nitrogen ejection are investigated to analyze their impacts on suppressing base heating and provide an insight into the intrinsic mechanisms. This investigation justifies the negative effect of large total temperature and reveals the unexpected non-monotonic impact of total pressure on reducing base heating. The present work indicates the necessity of restricting total pressure and total temperature within a suitable range in the design of nitrogen ejection to suppress rocket base heating.

Section snippets

Geometry and mesh

One of the rocket configurations in Musial's wind tunnel tests [3] is used to investigate the effect of the inlet total pressure and total temperature of nitrogen ejection on suppressing the base heating. Fig. 1 shows the geometry of the four-nozzle sub-scale rocket used in the present work, where $r_{b} = 152.4$ mm, $D_{t} = 21.463$ mm, $D_{e} = 74.676$ mm, $L / D_{e} = 1.53$ , $D_{s} / D_{e} = 1.67$ . Based on the geometric symmetry, a 1/8 model is adopted to reduce computational costs. As is shown in Fig. 2, tetrahedral meshes are

Computational method

The compressible Navier-Stokes equations adopted in the present work are given as $\frac{\partial ρ}{\partial t} + \nabla \cdot (ρ \vec{v}) = 0$ $\frac{\partial}{\partial t} (ρ \vec{v}) + \nabla \cdot (ρ \vec{v} \vec{v}) = - \nabla p + \nabla \cdot (μ_{e f f} \nabla \vec{v})$ $\frac{\partial}{\partial t} (ρ E) + \nabla \cdot (\vec{v} (ρ E + p)) = \nabla \cdot (k_{e f f} \nabla T - \sum h_{j} \vec{J_{j}} + τ_{e f f} \cdot \vec{v}) + S_{h}$ where $μ_{e f f}$ and $k_{e f f}$ are effective viscosity and effective thermal conductivity respectively, and the term $\sum h_{j} \vec{J_{j}}$ denotes the energy transport due to species diffusion. $S_{h}$ is the energy source term corresponds to the finite-rate chemical reactions. An implicit density-based solver is used to solve the Reynolds-Averaged

Base flow regimes

Base flow regimes are investigated to gain a deep insight into the mechanisms of base heating. First of all, flow regimes with and without nitrogen ejection are compared. Fig. 5 indicates the flow regimes for the two cases. It is observed that those two flow regimes have some similar characteristics. The exhaust plumes expand once flowing outside the nozzles, and subsequently a high-pressure region is formed after the collision among the plumes. The collided plumes are then reversed by the

Conclusion

This work has validated the effectiveness of nitrogen ejection on suppressing base heating by numerical simulation. Moreover, the impact of nitrogen ejection total pressure and total temperature on heat flux suppression has been deeply analyzed, and the intrinsic mechanisms have been further revealed. Conclusions are summarized below:

1.
Nitrogen ejection can significantly reduce the heat flux on the base plate and external nozzle walls by suppressing reverse flow. For the cases investigated, the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Analyzing the impact of nitrogen ejection on suppression of rocket base heating

Abstract

Introduction

Section snippets

Geometry and mesh

Computational method

Base flow regimes

Conclusion

Declaration of Competing Interest

Aerosp. Sci. Technol.

Aerosp. Sci. Technol.

Int. J. Heat Mass Transf.

Int. J. Hydrog. Energy

Acta Astronaut.

Aerosp. Sci. Technol.

Saturn base heating handbook

Some studies of the flow pattern at the base of missiles with rocket exhaust jets

Base flow characteristics for Several Four-Clustered Rocket Configurations at Mach Numbers from 2.0 to 3.5

Investigation of Base Flow on a Space Rocket with Plumes

Numerical Study of Base Flow Induced by Exhaust Plume Impingement

An integrated CFD tool for lunch vehicles base-heating analyses

Numerical simulation of the base flow and heat transfer characteristics of a four-nozzle clustered rocket engine

Numerical analysis of plume heating environment for H-IIA launch vehicle during powered ascent