Modified Pressure Loss Model for T-junctions of Engine Exhaust Manifold

The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.

Tip Clearance Flows in Turbine Cascades

This article describes the effects of some factors on the tip clearance flow in axial linear turbine cascades. The measurements of the total pressure loss coefficient are made at the cascade outlets by using a five-hole probe at exit Mach numbers of 0.10, 0.14 and 0.19. At each exit Mach number, experiments are performed at the tip clearance heights of 1.0%, 1.5%, 2.0%, 2.5% and 3.0% of the blade height. The effects of the non-uniform tip clearance height of each blade in the pitchwise direction are also studied. The results show that at a given tip clearance height, generally, total pressure loss rises with exit Mach numbers proportionally. At a fixed exit Mach number, the total pressure loss augments nearly proportionally as the tip clearance height increases. The increased tip clearance heights in the tip regions of two adjacent blades are to be blame for the larger clearance loss of the center blade. Compared to the effects of the tip clearance height, the effects of the exit Mach number and the pitchwise variation of the tip clearance height on the cascade total pressure loss are so less significant to be omitted.

Numerical Analysis and Experimental Validation of a Submerged Inlet on the Plane Surface

In order to get a deep insight of a submerged inlet on the plane surface, the integrated flow field of the inlet and fuselage has been numerically studied. The investigation is mainly focused on the formation of the total pressure distribution at the exit of the inlet, the structure of the inner flow and the effects of the boundary layer along the fuselage on the performance of the inlet. Moreover, in comparison with the experimental data at different angles of attack, yaws and mass flow ratios, the reliabilities of the computational fluid dynamics（CFD） studied are verified. Results indicate： （1） the CFD results agree well with the experiment results and the relative errors of the total pressure coefficient is less than 1% ; （2） at the inlet＇s exit, the contour of total pressure obtained by CFD is similar to the experiment result except the contour in the low total pressure zone in CFD is slightly larger; （3） the secondary flow at the cross section behave as two counter-rotating vortices. Along the flow direction, the fields influenced by the vortex pair transport downstream and expand to the whole section at the exit; （4） the total pressure loss at the exit of the submerged inlet can be divided into external loss and internal loss. Usually, the external loss is greater than the internal loss, and both decrease with the augment of the Mach number at the exit. In addition, when the angle of attack ranges from -2° to 8°, the total pressure coefficient ascends gradually, due to the reduction of the external loss caused by the less boundary layer flow captured and the invisible change of the internal loss.

Numerical Study on Aerodynamic Performance of CK Drone Aircraft Air Inlet in Maneuvering Flight

In view of the engineering background that CK drone aircraft needs modification and upgrading to improve its maneuvering performance,numerical research and analysis of air inlet aerodynamic performance are carried out.Firstly,based on the introduction of the theoretical knowledge involved in aircraft maneuvering flight,parameters such as aircraft attitude and engine mass flow etc.required for the aerodynamic performance calculation of CK drone aircraft air inlet are determined.By analyzing the test data of WP6 engine inlet distortion simulation board,the typical indexes are extracted as the basis for evaluating the air inlet performance of CK drone aircraft.Then,the aerodynamic characteristics of the inlet of CK drone aircraft under different maneuvering conditions are numerically studied,and the total pressure recovery coefficient and pressure distortion index of the outlet section are obtained.Several conclusions and suggestions are formed after the study.When CK drone aircraft flies at positive angle of attack,the inlet has good aerodynamic characteristics,which can meet the requirements of engine intake during high maneuverable flight.In the flight of negative angle of attack,the total pressure loss and pressure distortion at the outlet section of air inlet increase sharply,which cannot guarantee the stable working of the engine.On the premise that the aircraft attitude is satisfied,CK drone aircraft can use three engine thrust states of"Rated","Modified rated"and"Maximum"for high maneuverable flight.

Effect of Impeller Geometry and Tongue Shape on the Flow Field of Cross Flow Fans

Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans.Three impellers(Ⅰ，Ⅱ，Ⅲ）having same outer diameter,but different radius ratio and blade angles were employed for the investigation.Each impeller was tested with two tongue shapes.Flow survey was carried out for each impeller and tongue shape at two flow coefficients.and for each flow coefficient at different circumferential positions.The flow is two-dimensional along the blade span except near the shrouds.The total pressure developed by the impellers in each case is found to be maximum at a circumferential position of around 270°.The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry,but they vary considerably at exit of the impellers.Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure.Higher diffusion and smaller vortex size are the reasons for better performance of impeller Ⅲwith tongue T2。

Experimental Investigations of the Three-DimensionalFlow in a Large Deflection Turbine Cascade with Tip Clearance

Results obtained from an experbontal study of the threedimensional flow survey within and exit of a large defiection linear turbine cascade are presented for a tip clearance levels of 0.08, 1.5, 3.0 percent of chord and compared with the help of boundary layer probes and that within and exit of a blade passage was done with a miniaturised five hole probe. End wall and blade tip surface static pressures were also obtained, in addition to flow visualisation studies. A strong horse-shoe vortex forms in front of the leading edge for zero clearance whereas this vortex does not appear for 3 percent clearance indicating that for large clearance the pressure forces have dominating infiuence than the viscous forces. In addition to normally known clearance vortex, a small tip separation vortex was noticed on the blade tip surface inside the tip gap. Due to the area contraction caused by the tip separation vortex, the fluid movign towards the tip gap from the pressure side is accelerated. Downstream of the vortex, the endwall pressure increases due to flow mixing. Both vortices increase in size and strength along the chord. The miring is incomplete in the aft portion of the blade. The tip gap velocity profiles exhibit wak like characteristics especially at axial positions where the mixing is incomplete. The passage vortex in the present investigations did not diminish with increase in clearance. The discharge coefhcient and the total pressure loss coefficient within the tip gap show similar tendency with lower values near the leading and trailing edge regions.