Innovative Design and Additive Manufacturing of Regenerative Cooling Thermal Protection System Based on the Triply Periodic Minimal Surface Porous Structure

The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.

Turbulence Statistics of Thermo-Buoyancy Supercritical Fuel Flow in a Regenerative Cooling Channel

Active regenerative cooling with supercritical hydrocarbon fuel is considered as the most promising thermal protection method.The existence of buoyancy force would lead to strongly anisotropic flow and thermal transport characteristics.It is closely related to the cooling performance of the engine.To elucidate the mechanisms of turbulent transport,the large eddy simulation(LES) was performed to assess turbulence statistics within different turbulence scales.The results indicated that the buoyancy and inertial force together dominated the change of turbulent structure.Moreover,the spatial thermal buoyancy effect significantly suppressed the vertical velocity fluctuation.This is due to the laminar motion caused by the buoyancy force,thereby weakening the thermal transport.For the statistics of velocity fluctuation,it was found that the buoyancy force and inertial force greatly weaken the vertical and streamwise velocity fluctuation,respectively.For the statistics of thermal transport,the results pointed out that the near-wall heat transport characteristics need to be paid more attention.The thickness of the temperature mixing boundary layer led to the attenuation of vertical heat flux,which inhibited vertical temperature diffusion and predisposed to extreme conditions of heat transfer deterioration.The results can enhance the academic understanding of the heat transfer mechanism of supercritical fluids,and give guidance for further applications of thermal protection.

Experimental study on flow excursion instability of supercritical hydrocarbon fuel in scramjet regenerative cooling parallel channels

Flow instability of supercritical hydrocarbon fuel is a crucial issue in scramjet regenerative cooling structure. In this study, flow excursion instability and flow distribution in parallel tubes were experimentally studied for supercritical fluids. Two types of flow excursion occur in a single tube. Type Ⅰ and Type Ⅱ excursions, and they are corresponding to decreasing and increasing flow rate respectively. They can trigger flow maldistribution between parallel tubes and the hysteresis phenomenon of flow distribution. The effects of system parameters, including inlet temperature,system pressure, and heat flux, on flow distribution were analyzed. In addition, the relationship between flow excursion and the pseudo-critical interval proposed in the literature was established according to the heated tube outlet temperature at the onset of flow instability. Finally, the flow excursion instability boundary was obtained using two dimensionless parameters. These experimental results can provide helpful insight on the mechanism of Scramjet regenerative cooling.

Working state map of hydrocarbon fuels for regenerative cooling

Regenerative cooling by endothermic hydrocarbon fuel(EHF)is one of the most promising techniques for thermal management of supersonic or hypersonic aircraft.How to maintain the fuel working in proper states is an important issue to maximize the cooling potential of EHT.This work proposes a novel working state map,including risking zone(RZ),thermal cracking zone(TCZ),supercritical zone(SupZ)and subcritical zone(SubZ),to differentiate possible working states of an EHF during regenerative cooling.Using n-decane flowing in a circular tube as an example,the boundaries of four zones are determined by numerical simulation covering different heat fluxes(0.2-4.0 MW·m^(-2))and mass flow rates(0.5-10.5 g·s^(-1))under two operating pressures(3.45 and 5.00 MPa).Empirical correlations for three boundary lines are obtained and the maximum cooling capacity is identified,as well as the identification of the pressure effect.The revelation of such new perspective of regenerative cooling is of great implication to the design and optimization of cooling system for future thermal management.

Regenerative Cooling for Liquid Rocket Engines

Heat transfer in the thrust chamber is of great importance in the design of liquid propellant rocketengines. Regenerative cooling is an advanced method which can ensure not only the proper runningbut also higher performance of a rocket engine. The theoretical model is complicated, it relates to fluiddynamics, heat transfer, combustion, etc... In this papers a regenerative cooling model is presented.Effects such as radiation, heat transfer to environment, variable thermal properties and coking areincluded in the model. This model can be applied to all kinds of liquid propellant rocket engines aswell as similar constructions. The modularized computer code is completed in the work.

Effect of Inlet and Outlet Manifolds on Regenerative Cooling in LOX/Methane Thrust Chambers

Regenerative cooling is considered one of the most effective cooling methods used in liquid rocket engines and has been widely studied in recent years.But the effect of the non-uniform flow in cooling channels caused by inlet and outlet manifolds did not attract much attention.In this paper,we carried out the coupled flow and heat transfer of combustion and regenerative cooling in a LOX/Methane (LOX means liquid oxygen) engine and compared the results with and without manifolds.Then,three different configurations of the inlet and outlet manifolds were also discussed.The results show that the parameters averaged in the circumferential direction are less affected by the manifolds.However,the existence of the manifolds will make the distribution of mass flow rate as well as wall temperature non-uniform along the circumferential direction.In addition,when the angles between inlet and outlet are 0°,90° and 180°,the maximum temperature difference along the circumference of throat increases by 90.1%,151.2% and 229.5%,respectively,compared with that without manifolds.This indicates that the larger the angle between inlet and outlet,the greater the non-uniformity of mass flow rate and wall temperature along the circumferential direction.As a result,extra thermal stress will be generated which could cause some negative effects on the rocket engines.

Gas film/regenerative composite cooling characteristics of the liquid oxygen/liquid methane (LOX/LCH4) rocket engine

The thermal protection of rocket engines is a crucial aspect of rocket engine design.In this paper,the gas film/regenerative composite cooling of the liquid oxygen/liquid methane(LOX/LCH4)rocket engine thrust chamber was investigated.A gas film/regenerative composite cooling model was developed based on the Grisson gas film cooling efficiency formula and the one-dimensional regenerative cooling model.The accuracy of the model was validated through experiments conducted on a 6 kg/s level gas film/regenerative composite cooling thrust chamber.Additionally,key parameters related to heat transfer performance were calculated.The results demonstrate that the model is sufficiently accurate to be used as a preliminary design tool.The temperature rise error of the coolant,when compared with the experimental results,was found to be less than 10%.Although the pressure drop error is relatively large,the calculated results still provide valuable guidance for heat transfer analysis.In addition,the performance of composite cooling is observed to be superior to regenerative cooling.Increasing the gas film flow rate results in higher cooling efficiency and a lower gas-side wall temperature.Furthermore,the position at which the gas film is introduced greatly impacts the cooling performance.The optimal introduction position for the gas film is determined when the film is introduced from a single row of holes.This optimal introduction position results in a more uniform wall temperature distribution and reduces the peak temperature.Lastly,it is observed that a double row of holes,when compared to a single row of holes,enhances the cooling effect in the superposition area of the gas film and further lowers the gas-side wall temperature.These results provide a basis for the design of gas film/regenerative composite cooling systems.

System Design and Analysis of Hydrocarbon Scramjet with Regeneration Cooling and Expansion Cycle

A new expansion cycle scheme of the scramjet engine system including a hydrocarbon-fuel-based(kerosene)regenerative cooling system and supercritical/cracking kerosene-based turbo-pump was proposed in this paper.In this cycle scbeme,the supercritical/cracking kerosene with high pressure and high temperature is formed through the cooling channel.And then,in order to make better use of the high energy of the supercritical/cracking fuel,the supercritical/cracking kerosene fuel was used to drive the turbo-pump to obtain a high pressure of the cold kerosene fuel at the entrance of the cooling channel.In the end,the supercritical/cracking kerosene from the turbine exit is injected into the scramjet combustor.Such supercritical/cracking kerosene fuel can decrease the fuel-air mixing length and increase the combustion efficiency,due to the gas state and low molecular weight of the cracking fuel.In order to ignite the cold kerosene in the start-up stage,the ethylene-assisted ignition subsystem was applied.In the present paper,operating modes and characteristics of the expansion cycle system are first described.And then,the overall design of the system and the characterisitics of the start-up process are analyzed numerically to investigate effects of the system parameters on the scramjet start-up performance.The results show that the expansion cycle system proposed in this paper can work well under typical conditions.The research work in this paper can help to make a solid foundation for the research on the coupling characteristics between the dynamics and thermodynamics of the scramjet expansion cycle system.

Damage localization effects of the regeneratively-cooled thrust chamber wall in LOX/methane rocket engines

To investigate the damage localization effects of the thrust chamber wall caused by combustions in LOX/methane rocket engines, a fluid-structural coupling computational methodology with a multi-channel model is developed to obtain 3-demensioanl thermal and structural responses.Heat and mechanical loads are calculated by a validated finite volume fluid-thermal coupling numerical method considering non-premixed combustion processes of propellants. The methodology is subsequently performed on an LOX/methane thrust chamber under cyclic operation. Results show that the heat loads of the thrust chamber wall are apparently non-uniform in the circumferential direction. There are noticeable disparities between different cooling channels in terms of temperature and strain distributions at the end of the hot run phase, which in turn leads to different temperature ranges, strain ranges, and residual strains during one cycle. With the work cycle proceeding, the circumferential localization effect of the residual strain would be significantly enhanced. A post-processing damage analysis reveals that the low-cycle fatigue damage accumulated in each cycle is almost unchanged, while the quasi static damage accumulated in a considered cycle declines until stabilized after several cycles. The maximum discrepancy of the predicted lives between different cooling channels is about 30%.

Development of Preliminary Design Program for Combustor of Regenerative Cooled Liquid Rocket Engine

An integrated program was established to design a combustor for a liquid rocket engine and to analyze regenerative cooling results on a preliminary design level.Properties of burnt gas from a kerosene-LOx mixture in the combustor and rocket performance were calculated from CEA which is the code for the calculation of chemical equilibrium.The heat transfer of regenerative cooling was analyzed by using SUPERTRAPP code for coolant properties and by one-dimensional correlations of the heat transfer coefficient from the combustor liner to the coolant.Profiles of the combustors of F-1 and RS-27A engines were designed from similar input data and the present results were compared to actual data for validation.Finally,the combustors of 30 tonf class,75 tonf class and 150 tonf class were designed from the required thrust,combustion chamber,exit pressure and mixture ratio of propellants.The wall temperature,heat flux and pressure drop were calculated for heat transfer analysis of regenerative cooling using the profiles.

Thermal-structural analysis of regeneratively-cooled thrust chamber wall in reusable LOX/Methane rocket engines

To predict the thermal and structural responses of the thrust chamber wall under cyclic work,a 3-D fluid-structural coupling computational methodology is developed.The thermal and mechanical loads are determined by a validated 3-D finite volume fluid-thermal coupling computational method.With the specified loads,the nonlinear thermal-structural finite element analysis is applied to obtaining the 3-D thermal and structural responses.The Chaboche nonlinear kinematic hardening model calibrated by experimental data is adopted to predict the cyclic plastic behavior of the inner wall.The methodology is further applied to the thrust chamber of LOX/Methane rocket engines.The results show that both the maximum temperature at hot run phase and the maximum circumferential residual strain of the inner wall appear at the convergent part of the chamber.Structural analysis for multiple work cycles reveals that the failure of the inner wall may be controlled by the low-cycle fatigue when the Chaboche model parameter c3= 0,and the damage caused by the thermal-mechanical ratcheting of the inner wall cannot be ignored when c3〉 0.The results of sensitivity analysis indicate that mechanical loads have a strong influence on the strains in the inner wall.

Review on active thermal protection and its heat transfer for airbreathing hypersonic vehicles

Hypersonic vehicles with turbojet, ramjet, and scramjet engines are expected to be widely applied to future transportation systems. Due to high-speed flight in the atmosphere, body outer surfaces suffer strong aerodynamic heating, and on the other hand, combustion chamber inter walls are under extremely high temperature and heat flux. Therefore, more efficient and stable active cooling technologies are required in hypersonic vehicles, such as regenerative cooling, film cooling, and transpiration cooling, as well as their combinations. This paper presents a comprehensive literature review on three active cooling methods, i.e., regenerative cooling, film cooling, and transpiration cooling, and deeply analyzes the mechanism of each cooling method, including the fluids flow, heat transfer, and thermal cracking characteristics of different hydrocarbon fuels in regenerative cooling,the heat transfer and flow mechanism of film cooling under supersonic mainstream conditions, and the heat transfer and flow mechanism of transpiration cooling.

Three-dimensional numerical study of supercritical pressure effect on heat transfer of cryogenic methane

A three-dimensional numerical study of the turbulent convective heat transfer of the cryogenic methane flowing inside a square engine cooling channel under supercritical pressures was systematically conducted.Numerical results indicate that increasing the fluid pressure results in enhanced heat transfer of the cryogenic methane under supercritical pressures.At the pseudo-critical temperature under a corresponding supercritical pressure,drastic property variations cause heat transfer deterioration and sharp wall temperature increase at a high wall heat flux of 7MW/m2.A modified Jackson and Hall heat transfer equation,which can be used for supercritical heat transfer calculations of the cryogenic methane,has been successfully established in this paper.

Experimental investigation of nitrogen flow boiling heat transfer in a single mini-channel

Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 kg/(m^2·s),the inlet pressure ranged from 630 to 1080 kPa,and the heat flux ranged from 0 to 223.2 kW/m^2.Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined.Results showed that within the limited test conditions,the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance.Three heat transfer trends were identified with increasing heat flux.At low heat fluxes,the heat transfer coefficient increases first and then decreases with vapour quality.At intermediate heat fluxes,the heat transfer coefficient versus the vapour quality presents an inverted"U"shape.At high heat fluxes,a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon.The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception.The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure.A modified experimental correlation(mean absolute error(MAE)=19.3%)was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.

Model validation and parametric study of fluid flows and heat transfer of aviation kerosene with endothermic pyrolysis at supercritical pressure

The regenerative cooling technology is a promising approach for effective thermal protection of propulsion and power-generation systems.A mathematical model has been used to examine fluid flows and heat transfer of the aviation kerosene RP-3 with endothermic fuel pyrolysis at a supercritical pressure of 5 MPa.A pyrolytic reaction mechanism,which consists of 18 species and 24 elementary reactions,is incorporated to account for fuel pyrolysis.Detailed model validations are conducted against a series of experimental data,including fluid temperature,fuel conversion rate,various product yields,and chemical heat sink,fully verifying the accuracy and reliability of the model.Effects of fuel pyrolysis and inlet flow velocity on flow dynamics and heat transfer characteristics of RP-3 are investigated.Results reveal that the endothermic fuel pyrolysis significantly improves the heat transfer process in the high fluid temperature region.During the supercritical-pressure heat transfer process,the flow velocity significantly increases,caused by the drastic variations of thermophysical properties.Under all the tested conditions,the Nusselt number initially increases,consistent with the increased flow velocity,and then slightly decreases in the high fluid temperature region,mainly owing to the decreased heat absorption rate from the endothermic pyrolytic chemical reactions.

Thermodynamic analysis for a chemically recuperated scramjet

Endothermic hydrocarbon fuel is regarded as an optimal fuel for a scramjet with regenerative cooling,which provides extra cooling through endothermic chemical conversion to avoid the severly limited cooling capacity when conventional fuels are adopted for cooling.Although endothermic cooling is proposed from the view point that the heat sink of a conventional fuel is insufficient,the heat-absorbing through endothermic chemical reaction is actually a chemical recuperation process because the wasted heat dissipated from the engine thermal structure is recovered through the endothermic chemical reaction.Therefore,the working process of a scramjet with endothermic hydrocarbon fuel cooling is a chemical recuperative cycle.To analyze the chemical recuperative cycle of a chemically recuperated scramjet engine,we defined physical and chemical recuperation effectivenesses and heating value increment rate,and derived engine performance parameters with chemical recuperation.The heat value benefits from both physical and chemical recuperations,and it increases with the increase in recuperation effectiveness.The scramjet performance parameters also increase with the increase in chemical recuperation effectiveness.The increase in chemical recuperation effectiveness improves both the performances of the fuel cooling system and the combustion system.The results of analysis prove that the existence of a chemical recuperation process greatly improves the performance of the whole scramjet.

Numerical investigation of low cycle fatigue life for channel wall nozzles

The thermal-structural response and low cycle fatigue life of a three-dimensional(3D)channel wall nozzle with regenerative cooling were numerically investigated by coupling the finite volume fluid-thermal method,nonlinear finite element thermal-structural analysis and local strain methods.The nozzle had a high area ratio(nozzle exit area divided by throat area)under cyclic working loads.Parametric studies were carried out to evaluate the effects of channel structural parameters such as channel width,channel height,liner thickness and rib width.Results showed that the integrated effects of three-dimensional channel structure and load distribution caused serious strain,which mainly occurred at the intersectant regions of liner wall on the gas side and the symmetric planes of channel and rib.The cooling effect and channel structural strength were significantly improved as the channel width and height decreased,leading to substantial extension of the nozzle service life.On the other hand,the successive decrease in liner thickness and rib width apparently increased the strain amplitude and residual strain of channel wall nozzle during cyclic work,significantly shortening the service life.The present work is of value for design of the channel wall nozzle to prolong its cyclic service life.