Opposing Jet Concept Research Articles

Parameter study on drag and heat reduction of a novel combinational spiked blunt body and rear opposing jet concept in hypersonic flows

A novel combinational configuration is proposed for drag and heat reduction in this paper, the CFD numerical method is adopted to study its drag and heat reduction performance. The results show that the aerodisk enhances the compression of hypersonic free stream by the spike to reduce the intensity of reattachment shock wave. The rear jet pushes the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave as well. In addition, the low-temperature gas from rear jet can also cool the blunt body directly. Increasing the length-diameter ratio of the spike reduces the intensity of reattachment shock wave, the rear jet gas can be ejected farther to push the reattachment shock wave father away from the blunt body. Increasing the diameter of aerodisk enhances the compression of hypersonic free stream to reduce the intensity of reattachment shock wave, while the shock wave drag of spike gradually increases. Therefore, with the increase of diameter of aerodisk, the total drag coefficient of combinational configuration first decreases and then increases. The rear jet presents the long penetration mode and short penetration mode. Increasing the total pressure ratio and the size of nozzle can push the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave, more low-temperature gas can also be injected into the flow field to cool the blunt body effectively. Finally, the flat disk has better drag and heat reduction performance than conical disk and hemispherical disk.

A novel non-ablative thermal protection system with combined spike and opposing jet concept

In order to reduce the aerodynamic heating of the hypersonic vehicles, a combined non-ablative thermal protection system (CNA-TPS) is proposed in this paper, which consists of the blunt body, the spike, the front and rear jets. The heat reduction efficiency is studied by the CFD numerical method. The results show that the heat reduction efficiency of CNA-TPS is better than the other configurations, which verifies the advantage of the CNA-TPS. In addition, the effect of length of the spike, total pressure ratios and sizes of the front and rear jets are studied. The results show that the heat reduction efficiency of CNA-TPS increases with the increase of length of the spike, total pressure ratios and sizes of the front and rear jets. The improving rate of the heat reduction efficiency gradually decreases with the increase of length of the spike and total pressure ratios of the front and rear jets. The investigations in this paper show the feasibility and advantage of CNA-TPS in the future engineering applications.

Design exploration of combinational spike and opposing jet concept in hypersonic flows based on CFD calculation and surrogate model

The combined thermal protection system has led the drag and heat reduction of hypersonic reentry vehicles to a new developing direction. In order to obtain better resistance to aerodynamic drag and heat while maintain the work stability of the aircraft at the same time, the optimization design of the combined thermal protection system is indispensable. In this paper, a CFD numerical simulation method is combined with a surrogate model based multi-objective optimization algorithm to optimize the configuration of a combinatorial spike and opposing jet thermal protection system in a hypersonic flow with the freestream Mach number of 5.75. The obtained results show that when the total drag coefficient (Cd) and the heat fluxes on the head of the blunt body (Q) are the objective functions, the diameter ratio of the aerodisk to the blunt body bottom (d/D) has no significant effect on the drag and heat flux reduction, and it can be neglected in the optimization process. While the objective functions Cd and Q are affected by the three variables the length-to-diameter ratio of the aerospike (L/D), the jet pressure ratio (PR), and the nozzle radius (r0) in similar ways. Therefore, in this case, the optimization problem can be transformed into a single-objective optimization problem. The quadratic response surface model established by sample points obtained by the orthogonal experimental design method is of high simulation accuracy, with the determination coefficients of Cd and Q are 0.964 and 0.965 respectively, and there is only a difference of −6.96% in the objective function Cd, −0.93% in Q between the optimization results and the CFD results. The combined thermal protection system has better performance in both drag and heat reduction than the single spike or opposing jet systems. Compared with the pure blunt body, the total drag coefficient and heat flux on the head of the blunt body with the combined thermal protection system have significantly decreased, with the Cd goes down 86.66%, and the wall heat flux Q drops off 96.37%.

Detailed parametric investigations on drag and heat flux reduction induced by a combinational spike and opposing jet concept in hypersonic flows

In the current study, the flow field behavior induced by a novel combinational opposing jet and spike concept has been investigated numerically. A comprehensive analysis on the selections of the turbulence model and the height of the first grid point off the wall (Δx) has been conducted firstly. Then, this paper mainly focuses on the influences of the nozzle diameter (d0), the length-to-diameter ratio of the aerospike (L/D) and the jet pressure ratio (PR) on the flow field structures, the aerodynamic drag and heat properties. The results show that when d0 is 2 mm, adding the opposing jet to the single spiked blunt body has no help in modifying the high drag and heat environment. However, the combinatorial thermal protection system has a great contribution to reduce the drag and heat when d0 is 4 mm, with 45% and 38% drop on the wall Stanton number (St) and drag coefficient (Cd) respectively. The values of the wall heat flux, the static pressure and the drag coefficient decrease apparently when L/D increases from 1.0 to 1.5, while the drop rates of these indexes seem not so obvious when L/D rises from 1.5 to 2.0. Meanwhile, the introduction of the opposing jet creates a recirculation zone upstream the spike head, and there is a recirculation zone emerges downstream the aerodisk as well when L/D increases to 2.0. Both of the recirculation zones have alleviated the high temperature the aerodisk sustained significantly.

Drag reduction of supersonic blunt bodies using opposing jet and nozzle geometric variations

Passive and active flow control methods are used to manipulate flow fields to reduce acoustic signature, aerodynamic drag and heating experienced by blunt bodies flying at supersonic and hypersonic speeds. This paper investigate the use of active opposing jet concept in combination with geometric variations of the opposing jet nozzle to alleviate high wave drag formation. A numerical study is conducted to observe the effects of simple jet as well as jet emanating from a divergent nozzle located at the nose of a blunt hemispherical body. An initial discussion is presented of the complex shock wave pattern flow physics occurring when opposing jet ejected from a nozzle under various operating conditions interacts with the free stream flow. The complex flow physics that include long penetration and short penetration mode is studied in conjunction with effect on drag. The numerical setup consists of supersonic free stream flow interacting with an opposing sonic jet under varying pressure ratios. Initial computational results are validated by identifying prominent flow features as well as comparing available experimental data of surface pressure distributions. Preliminary validation is followed by the introduction of a divergent nozzle in the blunt body nose region. A series of numerical iterations are performed by varying nozzle geometric parameters that include nozzle divergent angle and nozzle length for a certain jet pressure ratio. Long penetration mode, short penetration mode as well as flow separations are captured accurately during the analysis. The results show a considerable reduction in drag by the use of a divergent nozzle. Specifically, 46% and 56% reduction in drag coefficient is achieved at pressure ratio of 0.6 and 0.8 respectively in the divergent nozzle cases as compared to the simple blunt body without any nozzle.

Multiobjective Design Optimization of Hypersonic Combinational Novel Cavity and Opposing Jet Concept

It attaches profound importance to conduct a survey on drag reduction and a thermal protection mechanism applied to the nose tip of hypersonic reentry vehicle due to severe aerodynamic drag and heating. The combinational forward-facing cavity and opposing jet configuration is an effective concept, and its performance could be partially improved when a maximum thrust nozzle contour is employed to substitute the conventional cavity configuration. However, the novel concept would not necessarily generate higher drag and heat reduction efficiency than the conventional one. Therefore, based on the verification of a numerical method, multiobjective design optimization of the combinational novel cavity and opposing jet concept is conducted to minimize both the drag force coefficient and heat load in the current study. The jet total pressure ratio and geometric dimensions are selected as design variables, and the sampling points are obtained numerically by using an optimal Latin hypercube design method. The multi-island genetic algorithm coupled with the kriging surrogate model integrated in Isight 5.5 has been employed to establish the approximate model and solve the Pareto-optimal front. The operating conditions located on the front are proved accurate by a computational fluid dynamics method, and higher drag and heat reduction efficiency can be realized than the conventional configuration at a relatively lower jet total pressure.

A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.