Fluidic throat control is one key technology of fixed geometry thrust vectoring nozzle. Based on CFD numerical simulation, the flow characteristics of fluidic throat control by high pressure secondary flow injected into throat of nozzle, and performance of nozzle were investigated. The coupling method of nozzle with fluidic throat control and aero-engine was proposed. Firstly, the approximate model of nozzle with fluidic throat control was established by combining the design of experiment and response surface methodology. Then the aero-engine simulation model with air extraction was established. And by mass flow balance and pressure balance relationship, the approximate model of fluidic throat control nozzle and aero-engine simulation model with air extraction were combined into coupling model. Simulation results show that, due to the high pressure secondary flow injected into nozzle throat, there exist obvious high and low speed layers near nozzle throat, and the secondary injection made the nozzle flow over expand. Through the check of validation of approximate model, it shows good precision and can be used for the coupling model. For coupling performance, under different air extraction ratios from fan, the operating point on compressor map did not move obviously, the change of throat area affects the fan operating points greatly, and made it move to the surge boundary. And in the simulation, at the air extraction ratio of 12%, the throat control ratio of 17.8% was achieved.

Embedding a row of typical cylindrical holes in a transverse slot can improve the cooling performance. Rectangular slots can increase the cooling effectiveness but is at the cost of decreasing of discharge coefficients. An experiment is conducted to examine the effects of an overlying transverse inclined trench on the film cooling performance of axial holes. Four different trench configurations are tested including the baseline inclined cylindrical holes. The influence of the geometry of the upstream lip of the exit trench and the geometry of the inlet trench on cooling performance is examined. Detailed film cooling effectiveness and heat transfer coefficients are obtained separately using the steady state IR thermography technique. The discharge coefficients are also acquired to evaluate the aerodynamic performance of different hole configurations. The results show that the film cooling holes with both ends embedded in slots can provide higher film cooling effectiveness and lower heat transfer coefficients; it also can provide higher discharge coefficients whilst retaining the mechanical strength of a row of discrete holes. The cooling performance and the aerodynamic performance of the holes with both ends embedded in inclined slots are superior to the holes with only exit trenched. To a certain extent, the configuration of the upstream lip of the exit trench affects the cooling performance of the downstream of the trench. The filleting for the film hole inlet avail the improvement of the cooling effect, but not for the film hole outlet. Comparing film cooling with embedded holes to unembedded holes, the overall heat flux ratio shows that the film holes with both ends embedded in slots and filleting for the film hole inlet can produce the highest heat flux reduction.

The exit-shaped holes can result in lower coolant momentum injection with greater surface coverage. The exit-trenched holes can also lower the coolant momentum. Thus, the cooling and aerodynamic performance of laterally diffused shaped holes and laterally trenched holes were numerically compared with same depth and same hole length and the reasons for the difference were also analyzed from the viewpoint of flow mechanism. The both end-shaped holes and both end-trenched holes were also compared to the exit-shaped holes and exit-trenched holes respectively. Owing to the better heat transfer performance of steam than that of air, the cooling characteristics of super heated vapor film and pure air film were numerically investigated using the multi phase model of FLUENT to study the effect of different vapor volume fraction on film cooling characteristics. It appears that the shaped holes is superior to the trenched holes in cooling and aerodynamic performance for the cases in the present study; for shaped holes, the difference between the exit-shaped hole and both end-shaped hole is negligible; But for trenched holes, the cooling effectiveness of both end-trenched hole and the exit-trenched holes is heavily dependent on the hole length to diameter ratio; for shorter hole length to diameter ratio, the cooling effectiveness of both end-trenched hole is superior to that of exit-trenched hole. For all the cases studied, the mixture injectant is better than pure air coolant, and the mixture exhibits greater cooling advantage in the far downstream region of the holes than in the near hole region. The super heated vapor film can improve the film cooling effectiveness; the vapor volume fraction increased by 20%, and the area average cooling effectiveness can increase by 5%.

The following five common topics in the modal Floor Response Spectrum (FRS) method are examined: 1) The relationship between the effective mass and the total mass; 2) Estimation of the base shear; 3) Identification of a local mode; 4) The uniform acceleration to be applied in the equivalent static analysis method; 5) Correction for the residual rigid modes. This paper shows the usage of effective mass in determining the base shear. A quantitative method based on the ranking of the importance of a mode and the importance of a mass in a mode is given, in addition to graphic animations, to exclude a local mode. It also provides a more realistic static method with a less overly conservative acceleration.

A numerical model was developed to study the effects of channel length and bend shape on the flow cross-over through the porous gas diffusion layer (GDL) and the pressure distribution in a PEM fuel cell flow plate with a serpentine channel flow system. Usually, on the cathode side of a PEM fuel cell, air flow through a flow plate with serpentine channels with certain lengths, to supply the oxygen to the catalyst layer for the chemical reaction. There is a porous GDL between the flow plate and the catalyst layer. Flow cross-over of air through the porous GDL from one part of the channel to another can occur because of the pressure differences existing between different parts of the channel. This cross-over causes the flow rate through the channel to vary with distance along the channel, and also has an influence on the pressure distribution through the plate and, eventually, the fuel cell performance. For the conventional channel flow, the pressure drop is proportional to the channel length. To study the importance of this channel length effect on the PEM fuel cell flow field with cross-over, the pressure distribution and flow rate variation along the channels have been examined by numerically solving for the flow through the plate and porous GDL assembly. Attention has been given here to serpentine channel flow systems with single and parallel channel patterns and with different numbers of passes. A 3-D, single-phase flow has been considered. It was assumed that the flow is steady and incompressible, and the flow through the porous diffusion layer can be described using the Darcy law. The governing equations have been written in dimensionless form using the channel width as the length scale and the mean velocity at the channel inlet as the velocity scale. The resulting set of dimensionless governing equations has been solved using the commercial finite element method (FEM) software package, FIDAP . The solution was obtained by simultaneously solving the equations for the flow in the channels and for the flow through the porous GDL. The solution depends on the following parameters, (1) the Reynolds number, Re , based on the channel width and on the mean velocity at the channel inlet, (2) the dimensionless GDL permeability, (3) the dimensionless channel length, (4) the bend shape, and (5) channel configurations. The main emphasis of this study was on the effect of channel length. The numerical results obtained indicate that the channel length has a significant effect on the flow cross-over through porous GDL and the pressure distribution in the flow plate.

Much effort has been expended in the past few years upon development of numerical models to obtain the detailed flow, current and temperature distributions in Polymer Electrolyte Membrane Fuel Cell (PEMFC). Therefore, the need for model validation also has increased to gain confidence in the accuracy of the numerical results. In the present work, a numerical model has been developed to study the pressure distribution in the flow field plate (FFP) and gas diffusion layer (GDL) assembly on the cathode side of a PEM fuel cell. The flow field plate has serpentine channels and the porous gas diffusion layer is adjacent to the flow field plate, to deliver the air to the catalyst layer where the electrochemical reaction occurs. Flow crossover of air through the porous GDL under the land from one part of the channel to another can occur, and this flow crossover affects the total pressure drop between the channel inlet and outlet, and the pressure difference between adjacent channels. The flow here has been assumed to be three-dimensional, steady, incompressible, isothermal and single-phase. The flow through the porous GDL has been described using the Darcy model. The governing equations have been written in dimensionless form and solved by using the commercial CFD solver, FIDAP . In parallel, experimental work has been conducted at the Queen’s-RMC Fuel Cell Research Center (FCRC), Canada, for comparison with the numerical results. The cathode FFP has a single serpentine channel. Flow of dry air at 20 °C and at 60 °C has been used for measuring pressure differences at specific locations in the flow field plate. The effects of Reynolds number, based on the mean channel width and the mean velocity at the channel inlet (values between 100 and 1500) have been studied. Other parameters that were considered are the land:channel width ratio (2:1 and 1:1) and the permeability of the GDL (values between 1.0E−19m 2 and 1.0E−10m 2 used). Good agreement was obtained between the numerical and experimental pressure distributions along the serpentine channel.

It is common in a PEM fuel cell to have the air flow through serpentine channels with a rectangular cross-sectional shape in a flow plate. There is a porous diffusion layer adjacent to this flow plate. Flow cross-over of air through the porous diffusion layer from one part of the channel to another can occur, as a result of the pressure differences between different parts of the channel, and it causes the flow rate through the channel to vary with distance along the channel and also has an influence on the pressure distribution along the channel. These changes in the pressure distribution as a result of cross-over can effect the fuel cell performance. In the present study the conditions under which cross-over occurs and the effects of the cross-over on the pressure distribution and local channel flow rates have been examined by numerically solving for the flow through the plate-porous layer assembly. Two flow channel arrangements have been considered: (i) a single serpentine channel flow system with different land widths between the channel sections (ii) a two-channel parallel serpentine flow system. A single phase flow has been considered. The governing equations have been written in dimensionless form using the channel width as the length scale and the mean velocity in the channel as the velocity scale. The resultant set of dimensionless equations has been numerically solved using a commercial finite element code, FIDAP. The solution was obtained by simultaneously numerically solving the dimensionless governing equations for the flow in the channels and for the flow through the porous gas diffusion layer. The numerical calculations were obtained using a commercial finite element code, FIDAP.