Numerical investigation on flow and heat transfer characteristics of supercritical RP-3 in inclined pipe

Numerical simulations of flow and heat transfer to supercritical RP-3 through the inclined tubes have been performed using LS k–e model embedded in Fluent. The physical properties of RP-3 were obtained using the generalized corresponding state laws based on the fourcomponent surrogate model. Mass flow rate is 0.3 g/s, system pressure is 3 MPa, inlet temperature is 373 K. Inclination of the inclined pipe varied from -90° to 90°, with heat flux varied from 300 k W/m^2 to 400 kW/m^2. Comparison between the calculated result and the experimental data indicates the range of error reasonable. The results of ±45° show that temperature inhomogeneity in inclined pipe produce the secondary flow in its cross section due to the buoyancy force. Depending on the strength of the temperature inhomogeneity, there will be two different forms of secondary flow and both contribute to the convective heat transfer in the pipe. The secondary flow intensity decreases when the inhomogeneity alleviates and thermal acceleration will play a leading role. It will have a greater impact on the turbulent flow to affect the convective heat transfer in the pipe. When changing the inclination, it affects the magnitude of the buoyant component in flow direction. The angle increases, the buoyancy component decreases. And the peak temperature of wall dominated by the secondary flow will move forward and increase in height.

Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional（2D） numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.

Computational Research on Rotating Channel by a Modified Anisotropic Turbulence Model

Based on the simplified format of the Reynolds stress equations,a fire-new rotational-modification method for the anisotropic turbulence model has been presented.A three-dimensional Navier-Stokes code with this new rotational modified k-ω turbulence models(β=0.1 and β=1) and the standard k-ω turbulence model have been used for the prediction of flow and heat transfer characteristics in a rotating smooth square channel.The Reynolds number Re based on the inlet velocity of the cooling air and hydraulic diameter is 6000.The rotating speed are 300,600,900,1200rpm respectively.The calculations results of using three turbulence models have been compared with the experimental data.The research results show that(1) the rotational modification coefficient Rf13 used in the new anisotropic k-ω model would increased/decreased the predictions of heat transfer on the trailing surface/leading surface compared to the standard k-ω model.And this tendency would be increased with the increased β.(2) The simulation performance of the standard k-ω model was well on the leading surface.However,on the trailing surface it under-predicted the heat transfer at high rotating speed.(3) The calculation results of the new anisotropic k-ω model with β=0.1 proposed by the present paper agreed well with experimental data,both on the leading and trailing surfaces.Besides,compared to 1,0.1 is a more appropriate magnitude of β at conditions in the present paper.

Effect of the protrusion shape on gas ingestion of two sealing structures

The windage loss caused by protrusion in a rotor–stator cavity has been studied in detail,and there are abundant fitting formulas that have been summarized to calculate the moment coefficients.Some other theorists have emphasized its effect on the sealing efficiency,proposing that installation of protrusion could alleviate gas ingestion.However,the protrusion shape which is an influential factor on the sealing efficiency has not been focused in previous research.Using the experimental method of measuring CO2 volume fraction,cavity pressure,and power consumption,we investigated the effects of several typical protrusion shapes on various parameters for two sealing structures,in order to obtain the optimal shape.Results showed that a variation of the protrusion shape had little impact on the static pressure,but the total pressure and the sealing efficiency increased in different degrees.Furthermore,even though the hexagon shape resulted in the highest sealing efficiency,we observed that the drop shape had the best overall performance in all of the eight models,which could result in higher efficiency of the turbine cavity.The combination of a radial seal structure and protrusion could improve sealing efficiency better.

Artificial intelligence aided design of film cooling scheme on turbine guide vane

In recent years,artificial intelligence(AI)technologies have been widely applied in many different fields including in the design,maintenance,and control of aero-engines.The air-cooled turbine vane is one of the most complex components in aero-engine design.Therefore,it is interesting to adopt the existing AI technologies in the design of the cooling passages.Given that the application of AI relies on a large amount of data,the primary task of this paper is to realize massive simulation automation in order to generate data for machine learning.It includes the parameterized three-dimensional(3-D)geometrical modeling,automatic meshing and computational fluid dynamics(CFD)batch automatic simulation of different film cooling structures through customized developments of UG,ICEM and Fluent.It is demonstrated that the trained artificial neural network(ANN)can predict the cooling effectiveness on the external surface of the turbine vane.The results also show that the design of the ANN architecture and the hyper-parameters have an impact on the prediction precision of the trained model.Using this established method,a multi-output model is constructed based on which a simple tool can be developed.It is able to make an instantaneous prediction of the temperature distribution along the vane surface once the arrangements of the film holes are adjusted.

Experimental Study on Heat Transfer and Flow Resistance in Improved Latticework Cooling Channels

Characteristics of heat transfer and flow resistance of the latticework (vortex) cooling channel with ribs truncated at their two ends were theoretically and experimentally studied compared with regular and smooth channels of the same configuration. The results showed: the heat transfer efficiency of the latticework channel with two slots was better than those of regular and smooth channels of the same configuration, its flow resistance situation in the slotted channel becomes quite complex; The flow resistances of 2 mm- and 4 mm-slotted channels were obviously lower than that of the regular channel, but they are still much higher than that of the smooth channel; Compared with the regular channel, the total heat transfer efficiencies of the slotted channels were pretty improved, among them the 4-mm slotted channel has the biggest enhancement. From the experimental results, it is obvious that the latticework channel with proper slots has a great prospect in the design of the inner cooling channels of turbine blades.

Artificial neural network analysis of the Nusselt number and friction factor of hydrocarbon fuel under supercritical pressure

This paper presents the Nusselt number and friction factor model for hydrocarbon fuel under supercritical pressure in horizontal circular tubes using an artificial neural network(ANN)analysis on the basis of the back propagation algorithm.The derivation of the proposed model relies on a large number of experimental data obtained from the tests performed with the platform of supercritical flow and heat transfer.Different topology structures,training algo-rithms and transfer functions are employed in model optimization.The performance of the optimal ANN model is evaluated with the mean relative error,the determination coefficient,the number of iterations and the convergence time.It is demonstrated that the model has high prediction accuracy when the tansig transfer function,the Levenberg-Marquardt training algo-rithm and the three-layer topology of 4-9-1 are selected.In addition,the accuracy of the ANN model is observed to be the highest compared with other classic empirical correlations.Mean relative error values of 4.4%and 3.4%have been achieved for modeling of the Nusselt number and friction factor respectively over the whole experimental data set.The ANN model estab-lished in this paper is shown to have an excellent performance in learning ability and general-ization for characterizing the flow and heat transfer law of hydrocarbon fuel,which can provide an alternative approach for the future study of supercritical fluid characteristics and the associ-ated engineering applications.

Computational research on film cooling under rotating frame by an anisotropic turbulence model

A new anisotropic k-o turbulence model was proposed in this paper.This new model,with the standard k-o model and the standard k-e model was embedded in our three-dimensional(3-D)Navier-Stokes code to compute rotational film cooling.In addition,the theoretical and numerical analysis on the influence of the Coriolis and buoyancy forces induced by the rotation was discussed in detail.Major findings of this study are as follows:⑴The new anisotropic k-o model preformed much better compared to its isotropic counterparts.(2)In the region of 6D-12D downstream the film hole,the numerical results of the new model were much closer to the experimental data than that in the region of 0-6D.(3)The constant density term can be balanced by the pressure gradient and would not influence the velocity and temperature distributions.But the centrifugal buoyancy force and the Coriolis force would change the trajectory of cooling air and temperature distributions.