Reynolds Stress Directivity Research Of The Confined Bidirectional Vortex

The Vortex Combustion Cold-Wall Chamber(VCCWC),which was proposed at the beginning of the 21th centry,is the typical case of the vortex technology engineering applications.The core of this VCCWC technology is the confined vortex.This special vortex has a unique velocity distribution of the reverse axial velocity.Thereby,an outer vortex was formed between the chamber wall and the inner reactive zone.This outer vortex plays the doubles roles of isolating the heat transfer and absorbing the heat transfer.In this paper,both numerical and analytical methods were utilized to deeply study the core flow of the VCCWC:the bidirectional vortex.The results of the bidirectional vortex theory and the data of existed experiments were used as the validation.The flow characteristic and the Reynolds Stress distributions of the bidirectional vortex were researched.At the same time,the doubles roles of the outer vortex were also revealed theoretically.The validation of the three rotation modify methods in bidirectional vortex simulation was numerical studied.The existed experimental data and the theory model of the bidirectional vortex were used as the reference.The simulation results of the RSM model was used as the contract.Both the three rotation modify methods were based on the isotropic hypothesis of the eddy viscosity turbulent models.The three modify methods included the extra rotation modify,the swirl modify and the curvature correction.It was found that,the performance of the extra rotation modify was the worst.There is almost no difference between the extra rotation modify or not.The swirl modify also provided almost nothing to improve under the default swirl factor of 0.06.The curvature correction method,on the other hand,carried out a significant improvement in the validation of tangential velocity,compared with the former two methods.Unfortunately,the validation of the axial velocity was still failure.The curvature correction method was still unable to reflect the unique feature of the bidirectional vortex,the reverse of the axial velocity closed to the wall.After the comparing of the three modify methods results with the experimental data and the theory model,it was suggested that the correctness of the numerical results in bidirectional vortex simulation could be confirmed only when both the tangential velocity and the axial velocity satisfied the existed bidirectional vortex theory at the same time.The Reynolds stress directivity of the bidirectional vortex was numerical studied.The Reynolds stress was introduced based on the Boussinesq isotropic hypothesis.The experimental data and theory model were used as the validation.It was found that,the Quadratic Pressure-Strain(QPS)RSM model was more excellent than the Linear Pressure-Strain(LPS)RSM model.The QPS RSM model improved the performance in the bidirectional vortex simulation.The Reynolds stress of the bidirectional vortex increased with the vortex Reynolds number.The directivity of the bidirectional vortex was remarkable.In the position of the maximum radial Reynolds stress,the difference between radial Reynolds stress and the tangential Reynolds stress increased to 150%of the tangential Reynolds stress.The Reynolds stress of the RNG model,which based on Boussinesq isotropic hypothesis,significantly differed from those two RSM models.The isotropic hypothesis made the Reynolds stress of the RNG model tend to be uniform.The worst performance of the RNG model in Reynolds stress simulation was the tangential Reynolds.The distribution trend was even wrong compared with those two RSM models.The distribution trend of the radial Reynolds stress and the axial Reynolds stress was relatively consistent with the RSM model results.But the values were still definitely wrong.In the further modifies focused on the eddy viscosity turbulent models considered the bidirectional vortex,the directivity of the Reynolds stress should be artificially introduced into those modifies.The influence of the shoulder width to the chamber radius ratio to the pressure and velocity field of the bidirectional vortex was numerically studied in the research of the VCCWC nozzle characteristics.The real VCCWC contracting nozzle was regards as the physical model.It was found that,the outlet vortex between the contracting section and the shoulder destroyed the fluency in case of the shoulder width to the chamber radius ratio was far greater than non-dimensional mantle radius.The greater ratio always could not satisfy the contracting ratio of the chamber nozzle.A virtual convergence section would form between the actual convergence sections in case of the shoulder width to the chamber radius ratio was far weaker than non-dimensional mantle radius.This virtual convergence section was also not depended on the shoulder width to the chamber radius ratio.In this case,one part of the inlet oxidizer flow would directly escape from the nozzle other than combustion with the fuel in chamber.This escape would significantly decrease the chamber efficiency.In the coupling research of the swirl condition and the bidirectional vortex characteristic,the simulation method was utilized.The experimental data and theory model were used as the validation.It was summarized that,the tangential velocity and the maximum tangential velocity decrease with the injection angle and length to diameter ration but increase with the injection pressure drop.The dimensionless radial positon of the maximum tangential velocity is kept around 0.19 in the whole chamber regardless of injection angle,injection pressure drop and the length to diameter ratio.For the different length to diameter ratio,the maximum tangential velocity increases for the length to diameter ratio of 1.0 but increases first and then decreases for the length to diameter ratio of 1.5 from the top of the chamber to the injection section.The axial decay rates of the tangential velocity and the maximum tangential velocity are kept within 3%.The dimensionless mantle radius is not kept constant but linearly increases from the top of the chamber to the injection section.The range of the dimensionless mantle radius is from 0.71 corresponding to 0.82.For the same injection angle,the impact of the length to diameter ratio to the magnitude of the maximum tangential velocity will strengthen with the increase of the injection pressure drop.The heat transfer process was theoretically analysis and re-modeled in the VCCWC.The heat equilibrium equations were built.It was summarized that,the oxidizer of the outer vortex played two roles in the heat transfer process of the VCCWC.The existed of the cold oxidizer flow in the outer vortex lead to the thermal resistance increased more than 14 times.In the process of the oxidizer flow towards the chamber end,one part of the transfer heat was absorbed by the oxidizer.As a result,the oxidizer of the outer vortex indeed acted as the cooling function.This cooling function lead to the ratio of the heat absorbed by the wall and the total heat transferred by the flame decreased to below 60%.Therefore,the oxidizer of the outer vortex played two roles of isolating and cooling the wall in the heat transfer process of the VCCWC.