Numerical investigation of blunt body’s heating load reduction with combination of spike and opposing jet

doi:10.1016/j.ijheatmasstransfer.2018.06.154

International Journal of Heat and Mass Transfer

Volume 127, Part C, December 2018, Pages 7-15

https://doi.org/10.1016/j.ijheatmasstransfer.2018.06.154 Get rights and content

Highlights

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The E-AUSMPWAS scheme, which performs well at all speeds, is adopted to conduct numerical analyses.
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The influence of the combinatorial thermal protection system on the total heating load is studied.
•
Models with spikes of different lengths and opposing jets of different pressures are compared systematically.

Abstract

In the design of the new generation reusable re-entry space vehicle, how to effectively reduce the heating load is important. In this paper, the thermal protection system combining the spike technology with the opposing jet technology is investigated. The three-dimensional compressible Reynolds Averaged Navier–Stokes (RANS) equations are simulated and Menter's shear stress transport (SST) turbulence model is applied. Also, the all-speed flux scheme called E-AUSMPWAS is adopted. The grid study is done and the numerical procedure is validated. Models with spikes of different lengths and opposing jets of different pressures are compared. Results show that the total pressure of the jet and the length of the spike have significant influences on the peak heating load of the vehicle. Also, the total heating load can reduce almost 95% compared to the base model. The findings suggest that the thermal protection system, which combines the spike technology with the opposing jet technology, is promising to be widely used in the design of the new generation reusable re-entry space vehicle.

Introduction

Nowadays, the new generation reusable re-entry space vehicle which is capable of carrying out deep space exploration has got wide attention. However, the structural coefficients of the existing spacecraft, such as Shen Zhou manned spacecraft and Apollo manned spaceship, are so large as to make payload not enough to achieve this goal [1]. Therefore, it is necessary to adopt more reusable lightweight materials and large-scale thin-wall structures to replace the tradition thermal protection method. Because the severe heating load is crucial to the design and optimization of the thermal protection system, how to effectively reduce the vehicle’s heating load is of great significance [2].

In general, various techniques have been studied to achieve the heating load’s reduction, such as spike [3], [4], [5], [6], [7], [8], [9], energy deposition [10], opposing jet [11], [12], [13], and their combinations [14], [15], [16], [17], [18], [19], [20]. As illustrated in Fig. 1, the spike technology splits the bow shock into multiple weaker shock waves and induces a large flow separation zone in the vicinity of the stagnation region. Therefore, it is capable of reducing the heating load by reconstructing the flow field. However, the heating load at the head of the spike is severe. Also, the shock/shock interaction and the reattachment of the separation zone at the shoulder make the peak heat flux high.

The opposing jet pushes the shock away from the stagnation region and forms a series of rich flow structures. Due to its wide application, a large number of studies have been carried out on this issue. Finely pointed out that the flow field induced by the opposing jet had the following three modes: the unsteady modes of the shock with oscillations, the steady modes of the shock without oscillations, and the medium mode between them [21]. Tian studied the influences of the jet Mach number, the angle of attack, and the free Mach number on the heating load’s reduction by adopting numerical methods [22]. Hayashi carried out numerical simulations and experiments to study the opposing jet’s method with his co-workers [23]. Also, Huang conducted similar analyses and obtained constructive conclusions [24]. However, the jet has to be with a large total pressure to form a stable flow field, which limits this method’s wide use.

To overcome the defects of the spike technology and the opposing jet technology, several combinatorial strategies were proposed. Among them, the thermal protection system by combining the spike technology with the opposing jet technology have been pursued by numerous scholars [25]. Experiments carried out by Liu and Jiang showed that the peak heating load was reduced remarkably by this combinatorial technology [26]. Huang numerically studied the technology’s performance in reducing drag [27]. Based on high precision numerical approach, Eghlima et al. found that the combinatorial technology could reduce the peak heating load greatly [20]. However, they only consider the peak heating load and ignore the total heating load. In fact, the total heating load is of much significance to the design of the thermal protection system.

In this paper, we will adopt numerical methods to study the influence of the thermal protection system, which combines the opposing jet technology with the spike technology, on both the peak heating load and the total heating load. Moreover, spikes with different lengths and jets with different total pressures are considered.

This manuscript is organized as follows. In the second section, we will briefly overview the governing equations and the computational methods we adopt. Validation for the code and numerical procedure, and the grid category are carried out in Secttion 3. The fourth section will illustrate the physical models which we analyze in this paper. Results and discussions will be presented in the 5th section. The last section contains the concluding remarks.

Section snippets

Governing equations

In this study, we adopt the following three-dimensional steady NS equations to numerically solve the flow fields [28], [29].

Continuity equation: $\frac{\partial ρ}{\partial t} + \frac{\partial ρ u_{i}}{\partial x_{i}} = 0$

Momentum equation: $\frac{\partial (ρ u_{i})}{\partial t} + \frac{\partial (ρ u_{i} u_{j})}{\partial x_{j}} = - \frac{\partial p}{\partial x_{i}} + \frac{\partial τ_{ij}}{\partial x_{j}}$

Energy equation: $\frac{\partial (ρ E)}{\partial t} + \frac{\partial (ρ u_{j} H)}{\partial x_{j}} = \frac{\partial (u_{i} τ_{ij} - {\dot{q}}_{j})}{\partial x_{j}}$ where ρ is the density, u_i is the i^th component velocity. Also, p is the static pressure, τ_ij is the shear stress term, ${\dot{q}}_{j}$ is the heat flux, E is the total energy, and H is the total enthalpy as follows $p = (γ - 1) [ρ E - \frac{1}{2} ρ (u^{2} + v^{2} + w^{2})]$ $E = e + \frac{1}{2} (u^{2} + v^{2} +$

Code validation and grid sensitivity analysis

In this section, we simulate the opposing jet of the sphere, which was studied experimentally, to validate the numerical procedure, grid generation strategy, and CFD code we adopt. The experimental model’s characteristic diameter is 50 mm [12]. The free Mach number is 3.98, the free total pressure is 1.37 MPa, the temperature of the solid wall is 295 K, and the free total temperature is 395 K. In addition, the rejecting gas is nitrogen with the Mach number 1.0 and the diameter of the nozzle

Physical model

In this paper, physical models depicted in Fig. 6 with the jets of different total pressures (Table 1) are investigated. The diameter of the sphere is 60 mm, the inner radius of the nozzle is 3 mm, and the outer radius of the nozzle is 5 mm [41]. Also, we adopt four different nozzles in this study. The first one is with the length 0 mm and called ‘LD0/4’, the second one is with the length 14.1 mm and called ‘LD1/4’, the third one is with the length 29.1 mm and called ‘LD2/4’, and the fourth one

Results and discussion

Mach number contours of different cases in the symmetry plane are depicted in Fig. 7. When the opposing jet is adopted, the bow shock is pushed away from the solid wall and the jet is expanded to form the shock disk. The supersonic jet passes through the Mach disk and slows down. The slowed flow interacts with the off-body shock and induces a free shear layer. Also, a separation zone exists around the nozzle and the head of the sphere.

As illustrated, with the total pressure of the jet

Concluding remarks

In this paper, we numerically study the influence of the thermal protection system, which combines the opposing jet technology with the spike technology, on both the peak heating load and the total heating load. Also, the spikes with different lengths and the jets with different total pressures are considered. Through systematic numerical analyses, several conclusions can be drawn as follows:

(1)
When the total pressure of the jet is 40kp and no spike is used, the off-body shock oscillates and makes

Conflict of interest

The authors declared that there is no conflict of interest.

Acknowledgements

This study was co-supported by the National Basic Research Program of China (No. 11271350). The first author is grateful to Master Ju Wang, University of Michigan, United States for some helpful advice.