Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,90...Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS （URANS）. Some typical linear and nonlinear eddy viscosity turbulence models （LEVM and NLEVM） and a quadratic explicit algebraic stress model （EASM） are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.展开更多
In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion ...In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code OpenFOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.展开更多
Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes （RANS） Equation method. The standard k - c turbulence and the modified Z-G-B cavitation...Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes （RANS） Equation method. The standard k - c turbulence and the modified Z-G-B cavitation models are employed. A measured nominal wake is used for the inlet velocity boundary condition. Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations. In addition, the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied. Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper. Comparisons demonstrate that the skewed propeller with a skew angle of 20~ is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.展开更多
The incompressible unsteady Reynolds-averaged Navier-Stokes(URANS)simulations are performed for a free-running container ship in maneuvering conditions:the starboard and portside turning circle simulations with 35...The incompressible unsteady Reynolds-averaged Navier-Stokes(URANS)simulations are performed for a free-running container ship in maneuvering conditions:the starboard and portside turning circle simulations with 35°rudder deflection.The validation variables include trajectory,motions,and propeller performances,and the prediction shows acceptable agreements against the experimental data.During the steady-state part of the turning,the inertial forces balancing the local forces are reported to quantitatively assess the centrifugal force which appears from the force equilibrium between the rudder,propeller,and the bare-hull.The study on the local flow focuses on finding the correlations between the propeller inflow and the propeller performance to investigate the differences in propeller performances during the portside and starboard turning.The preliminary simulations,performed with the grid triplet,comprise propeller open-water,resistance,and self-propulsion simulations,from which the validation studies and the studies for the local force and the local flow are fulfilled and applied for the main simulations.Both propeller and rudder are fully discretized and controlled,mimicking the experiment.Level-set,overset approach and Mentor’s SST model are employed for the free-surface capturing,large motion prediction,and turbulence closure.展开更多
Part 2 reports the validation,local force and local flow study results for the free-running added power simulations whose conditions are the same as the self-propulsion test except for the increased propeller rotation...Part 2 reports the validation,local force and local flow study results for the free-running added power simulations whose conditions are the same as the self-propulsion test except for the increased propeller rotational speed and the presence of wave.When targeting the same mean Froude number in the wave condition,the propeller requires the increased propeller rotational speed for the operation at the low advance ratio due to the added resistance.The test is performed at five different wavelengths in head waves and four different headings in the oblique waves.For the validation study,the time series of the validation variables is decomposed with discrete Fourier transform to extract the harmonic values.Validation variables are global parameters,including motions,propeller thrust,and torque coefficients,added power variables,and self-propulsion factors which show reasonable agreement against the experiment results and produces a similar error from the self-propulsion simulation.The local force study shows that the added resistance mostly appears at the bow due to the bow plunging during the short head wave and resonance condition.The contributions of the gravitational force and the buoyant force are found to increase as the stern motion exceeds the bow motion during the long head wave condition.The oscillation of the propeller performances shows correlation with the first harmonic amplitude of the propeller inflow.Heave,pitch,and roll decay tests are performed prior to the main test to assess the natural frequencies of the ship.Same as Part 1,a discretized propeller is used.展开更多
采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速...采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速度的影响,得到模型起飞过程中的受力变化趋势。模拟前通过分别计算标准模型的气动力和水动力并与实验数据对比,对数值计算方法进行了验证,模拟过程中通过VOF(volume of fluid)方法实现对自由液面界面的捕捉,最后通过对静水起飞过程中模型受力变化进行分析并与实验结果比较,对本文中的水气耦合数值计算进行了验证,计算结果表明,水上飞机低压载状态起飞过程中所受总阻力是缓慢增加的,并不会出现往复;同时水线高度逐渐下降,下降速度逐渐加快,且不会出现埋艏现象。展开更多
Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, t...Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of un- steady Reynold-averaged Navier-Stokes （URANS） and de- tached eddy simulation （DES） are utilized, respectively. Re- suits reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.展开更多
The broad implication of the paper is to elucidate the significance of the dynamic heaving motion in the aerodynamic performance of multi-element wings,currently considered as a promising aspect for the improvement of...The broad implication of the paper is to elucidate the significance of the dynamic heaving motion in the aerodynamic performance of multi-element wings,currently considered as a promising aspect for the improvement of the aerodynamic correlation between CFD,wind tunnel and track testing in race car applications.The relationship between the varying aerodynamic forces,the vortex shedding,and the unsteady pressure field of a heaving double-element wing is investigated for a range of mean ride heights,frequencies,and amplitudes,using a two-dimensional(2D)unsteady Reynolds-averaged Navier-Stokes(URANS)approach and an overset mesh method for modelling the moving wing.The analysis of the results shows that at high frequencies,i.e.,k≥5.94 and amplitudes a/c≥0.05 the interaction of the shear vorticity between the two elements results in the generation of cohering leading and trailing edge vortices on the flap,associated to the rapid variation of thrust and downforce enhancement.Both the occurrence and intensity of these vortices are dependent upon the frequency,amplitude,and mean ride height of the heaving wing.The addition of the flap significantly alters the frequency of the shed vortices in the wake and maintains the generation of downforce for longer time in ground proximity.The comparison with the static wing provides evidence that the dynamic motion of a race car wing can be beneficial in terms of performance,or detrimental in terms of aerodynamic correlation.展开更多
Gas turbine flows are complex and very difficult to be predicted accurately not only due to that they are inherently unsteady but also because the presence of many complex flow phenomena such as transition,separation,...Gas turbine flows are complex and very difficult to be predicted accurately not only due to that they are inherently unsteady but also because the presence of many complex flow phenomena such as transition,separation,substantial secondary flow,combustion and so on.Those complex flow phenomena cannot be captured accurately by the traditional Reynolds-Averaged Navier-Stokes(RANS)and Unsteady RANS(URANS)methods although they have been the main numerical tools for computing gas turbine flows in the past decades due to their computational efficiency and reasonable accuracy.Therefore,the desire for greater accuracy has led to the development and application of high fidelity numerical simulation tools for gas turbine flows.Two such tools available are Direct Numerical Simulation(DNS)which captures directly all details of turbulent flow in space and time,and Large Eddy Simulation(LES)which computes large scale motions of turbulent flow directly in space and time while the small scale motions are modelled.DNS is computationally very expensive and even with the available most powerful supercomputers today or in the foreseeable future it is still prohibitive to apply DNS for gas turbine flows.LES is the most promising simulation tool which has already reasonably widely used for gas turbine flows.This paper will very briefly review first the applications of LES in turbomachinery flows and then focus on two gas turbine combustor related flow cases,summarizing the current status of LES applications in gas turbines and pointing out the challenges that we are facing.展开更多
Attending WTO will bring about great effect on China, as well as Jiangsu Province. The paper analyzes the effect from the following aspects. Under the background of economical globalization, information development an...Attending WTO will bring about great effect on China, as well as Jiangsu Province. The paper analyzes the effect from the following aspects. Under the background of economical globalization, information development and knowledge - based economy, attending WTO will promote the dynamic mechanism of urbanization to tend to high - level tertiary, instead Of industry. Attending WTO will produce comprehensive influence on the industries of Jiangsu Privince, and speed the economical efficiency, which in turn accelerates the urbanization. Then it will do good to develop out - oriented economy and be propitious to hi - tech development zones, which enlarges built - area and urban residents. Attending WTO will gain much more foreign investment, which can improve the infrastructure and the investment environment, and ameliorate the distribution of cities and towns system in the long run.展开更多
The paper expounds the metallogenic characterist ic s of Jiawula multimetals deposit in China and Uran multimetals deposit in Mongol ia. Comparative study shows that both deposits are volcanic hydrothermal mineral iza...The paper expounds the metallogenic characterist ic s of Jiawula multimetals deposit in China and Uran multimetals deposit in Mongol ia. Comparative study shows that both deposits are volcanic hydrothermal mineral ization with same epoch(Mesozoic), same source, same temperature, and same miner al assemblage, but volcanic structure are different. Therefore, both deposits ca n draw on experience of each other and supplement in future of second time ore- prospecting, and point out the new direction of ore-prospecting.展开更多
文摘Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS （URANS）. Some typical linear and nonlinear eddy viscosity turbulence models （LEVM and NLEVM） and a quadratic explicit algebraic stress model （EASM） are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.
基金supported by the National Natural Science Foundation of China(Grant Nos.51379125,11272120)the National Key Basic Research Development Program of China(973Program,Grant No.2013CB036103)the High Technology of Marine Research Project of the Ministry of Industry and Information Technology of China
文摘In this paper, numerical prediction of ship motion responses in long-crest irregular waves by the URANS-VOF method is presented. A white noise spectrum is applied to generate the incoming waves to evaluate the motion responses. The procedure can replace a decade of simulations in regular wave with one single run to obtain a complete curve of linear motion response, considerably reducing computation time. A correction procedure is employed to adjust the wave generation signal based on the wave spectrum and achieves fairly better results in the wave tank. Three ship models with five wave conditions are introduced to validate the method. The computations in this paper are completed by using the solver naoe-FOAM-SJTU, a solver developed for ship and ocean engineering based on the open source code OpenFOAM. The computational motion responses by the irregular wave procedure are compared with the results by regular wave, experiments and strip theory. Transfer functions by irregular wave closely agree with the data obtained in the regular waves, showing negligible difference. The comparison between computational results and experiments also show good agreements. The results better predicted by CFD method than strip theories indicate that this method can compensate for the inaccuracy of the strip theories. The results confirm that the irregular wave procedure is a promising method for the accurate prediction of motion responses with less accuracy loss and higher efficiency compared with the regular wave procedure.
文摘Cavitating flows around skewed propellers are investigated numerically by means of the unsteady Reynolds Averaged Navier-Stokes （RANS） Equation method. The standard k - c turbulence and the modified Z-G-B cavitation models are employed. A measured nominal wake is used for the inlet velocity boundary condition. Predicted cavitating evolution processes and tip cavity patterns are compared with experimental observations. In addition, the influence of the skew angles on the cavitation and unsteadiness performances of propellers operating in a non-uniform wake is also studied. Results show that the modified Z-G-B cavitation model performs better to simulate the cavitating flow cases studied in this paper. Comparisons demonstrate that the skewed propeller with a skew angle of 20~ is the best choice for a given stern wake with a assigned thrust and the minimum force fluctuations.
基金This work was supported by the Office of Naval Research(Grant Nos.N00014-17-1-2083,N00014-17-1-2084).
文摘The incompressible unsteady Reynolds-averaged Navier-Stokes(URANS)simulations are performed for a free-running container ship in maneuvering conditions:the starboard and portside turning circle simulations with 35°rudder deflection.The validation variables include trajectory,motions,and propeller performances,and the prediction shows acceptable agreements against the experimental data.During the steady-state part of the turning,the inertial forces balancing the local forces are reported to quantitatively assess the centrifugal force which appears from the force equilibrium between the rudder,propeller,and the bare-hull.The study on the local flow focuses on finding the correlations between the propeller inflow and the propeller performance to investigate the differences in propeller performances during the portside and starboard turning.The preliminary simulations,performed with the grid triplet,comprise propeller open-water,resistance,and self-propulsion simulations,from which the validation studies and the studies for the local force and the local flow are fulfilled and applied for the main simulations.Both propeller and rudder are fully discretized and controlled,mimicking the experiment.Level-set,overset approach and Mentor’s SST model are employed for the free-surface capturing,large motion prediction,and turbulence closure.
基金This work was supported by the Office of Naval Research(Grant Nos.N00014-17-1-2083,N00014-17-1-2084).
文摘Part 2 reports the validation,local force and local flow study results for the free-running added power simulations whose conditions are the same as the self-propulsion test except for the increased propeller rotational speed and the presence of wave.When targeting the same mean Froude number in the wave condition,the propeller requires the increased propeller rotational speed for the operation at the low advance ratio due to the added resistance.The test is performed at five different wavelengths in head waves and four different headings in the oblique waves.For the validation study,the time series of the validation variables is decomposed with discrete Fourier transform to extract the harmonic values.Validation variables are global parameters,including motions,propeller thrust,and torque coefficients,added power variables,and self-propulsion factors which show reasonable agreement against the experiment results and produces a similar error from the self-propulsion simulation.The local force study shows that the added resistance mostly appears at the bow due to the bow plunging during the short head wave and resonance condition.The contributions of the gravitational force and the buoyant force are found to increase as the stern motion exceeds the bow motion during the long head wave condition.The oscillation of the propeller performances shows correlation with the first harmonic amplitude of the propeller inflow.Heave,pitch,and roll decay tests are performed prior to the main test to assess the natural frequencies of the ship.Same as Part 1,a discretized propeller is used.
文摘采用多相URANS(unsteady RANS)方法,针对水上飞机静水起飞过程中的性能分析,提出了一种新的数值模拟研究思路。通过考虑起飞过程中气动力和水动力之间的耦合影响、升力和浮力对水线位置高度变化的影响以及阻力和发动机推力对模型前进速度的影响,得到模型起飞过程中的受力变化趋势。模拟前通过分别计算标准模型的气动力和水动力并与实验数据对比,对数值计算方法进行了验证,模拟过程中通过VOF(volume of fluid)方法实现对自由液面界面的捕捉,最后通过对静水起飞过程中模型受力变化进行分析并与实验结果比较,对本文中的水气耦合数值计算进行了验证,计算结果表明,水上飞机低压载状态起飞过程中所受总阻力是缓慢增加的,并不会出现往复;同时水线高度逐渐下降,下降速度逐渐加快,且不会出现埋艏现象。
基金supported by the National Key Technology R&D Program(2009BAG12A03)the Major State Basic Research Development Program of China(2011CB711101)
文摘Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of un- steady Reynold-averaged Navier-Stokes （URANS） and de- tached eddy simulation （DES） are utilized, respectively. Re- suits reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.
文摘The broad implication of the paper is to elucidate the significance of the dynamic heaving motion in the aerodynamic performance of multi-element wings,currently considered as a promising aspect for the improvement of the aerodynamic correlation between CFD,wind tunnel and track testing in race car applications.The relationship between the varying aerodynamic forces,the vortex shedding,and the unsteady pressure field of a heaving double-element wing is investigated for a range of mean ride heights,frequencies,and amplitudes,using a two-dimensional(2D)unsteady Reynolds-averaged Navier-Stokes(URANS)approach and an overset mesh method for modelling the moving wing.The analysis of the results shows that at high frequencies,i.e.,k≥5.94 and amplitudes a/c≥0.05 the interaction of the shear vorticity between the two elements results in the generation of cohering leading and trailing edge vortices on the flap,associated to the rapid variation of thrust and downforce enhancement.Both the occurrence and intensity of these vortices are dependent upon the frequency,amplitude,and mean ride height of the heaving wing.The addition of the flap significantly alters the frequency of the shed vortices in the wake and maintains the generation of downforce for longer time in ground proximity.The comparison with the static wing provides evidence that the dynamic motion of a race car wing can be beneficial in terms of performance,or detrimental in terms of aerodynamic correlation.
文摘Gas turbine flows are complex and very difficult to be predicted accurately not only due to that they are inherently unsteady but also because the presence of many complex flow phenomena such as transition,separation,substantial secondary flow,combustion and so on.Those complex flow phenomena cannot be captured accurately by the traditional Reynolds-Averaged Navier-Stokes(RANS)and Unsteady RANS(URANS)methods although they have been the main numerical tools for computing gas turbine flows in the past decades due to their computational efficiency and reasonable accuracy.Therefore,the desire for greater accuracy has led to the development and application of high fidelity numerical simulation tools for gas turbine flows.Two such tools available are Direct Numerical Simulation(DNS)which captures directly all details of turbulent flow in space and time,and Large Eddy Simulation(LES)which computes large scale motions of turbulent flow directly in space and time while the small scale motions are modelled.DNS is computationally very expensive and even with the available most powerful supercomputers today or in the foreseeable future it is still prohibitive to apply DNS for gas turbine flows.LES is the most promising simulation tool which has already reasonably widely used for gas turbine flows.This paper will very briefly review first the applications of LES in turbomachinery flows and then focus on two gas turbine combustor related flow cases,summarizing the current status of LES applications in gas turbines and pointing out the challenges that we are facing.
文摘Attending WTO will bring about great effect on China, as well as Jiangsu Province. The paper analyzes the effect from the following aspects. Under the background of economical globalization, information development and knowledge - based economy, attending WTO will promote the dynamic mechanism of urbanization to tend to high - level tertiary, instead Of industry. Attending WTO will produce comprehensive influence on the industries of Jiangsu Privince, and speed the economical efficiency, which in turn accelerates the urbanization. Then it will do good to develop out - oriented economy and be propitious to hi - tech development zones, which enlarges built - area and urban residents. Attending WTO will gain much more foreign investment, which can improve the infrastructure and the investment environment, and ameliorate the distribution of cities and towns system in the long run.
文摘The paper expounds the metallogenic characterist ic s of Jiawula multimetals deposit in China and Uran multimetals deposit in Mongol ia. Comparative study shows that both deposits are volcanic hydrothermal mineral ization with same epoch(Mesozoic), same source, same temperature, and same miner al assemblage, but volcanic structure are different. Therefore, both deposits ca n draw on experience of each other and supplement in future of second time ore- prospecting, and point out the new direction of ore-prospecting.
