Numerical simulation of S-shaped inlet under the intake total pressure distortion

During the development of the stealth fighter, the S-shaped inlet enters the designer’s vision because it has better stealth than bump inlet and straight inlet. During the use of the S-shaped inlet, due to its structural reasons, secondary flow is likely to occur in the curved section, which directly causes the flow state to be changeable and complicated. Therefore, this paper takes the S-shaped inlet as the research object to analyzes the steady flow field simulation under uniform inlet condition and distortion inlet condition and analyze the flow field of the airflow and the total pressure of each section under the S-shaped inlet by changing the intake distortion conditions with CFX software. The results show that although the S-shaped inlet will occur total pressure distortion under uniform intake. However, when the S-shaped inlet work under certain flight conditions, the level of total pressure distortion will be smaller than the uniform inlet condition, which can improve the air intake performance. Finally, it can be inferred that with use of the S-shaped intake port, the deterioration of distortion may be prevented under certain specific intake conditions.

The effect of single-sided ribs on heat transfer and pressure drop within a trailing edge internal channel of a gas turbine blade

Convective cooling in a gas turbine blade internal trailing edge channel is often insufficient at the sharp trailing edge. This study examines convective heat transfer and pressure drop within a simplified trailing edge channel. The internal passage has been modeled as a right triangular channel with a 9° angle sharp corner. Smooth baseline and ribbed copper plates were heated from underneath via a uniform heat flux heater and examined via infrared thermography. Non-uniformity in the heat flux due to conduction is corrected by a RANS conjugate heat transfer calculation, which was validated by the mean velocity, friction factor, and temperature fields from experiments and LES simulations. Nusselt number distributions illustrate that surface heat transfer is increased considerably with ribs, and coupled with the vortices in the flow. Heat transfer at the sharp corner is increased by more than twofold due to ribs placed at the center of the channel, due to secondary flow. The present partially ribbed channel utilizes secondary flow toward the corner, and is presumed to have better thermal performance than a fully ribbed channel. Thus, it is important to set the appropriate rib length within the channel.

Hydrodynamic characteristics of lateral withdrawal with effects of the slope ratio

Lateral withdrawal is widely performed in water transfer and water supply projects. Hydrodynamic characteristics of intake are crucial to safe and stable operation. In this study, a 3-D numerical volume of fluid model was established and validated through experimental tests. Hydrodynamic characteristics and secondary flow were investigated under scenarios with the vertical slope and different slope ratios. The helix-shaped recirculation and surface vortex are generated, and the secondary flow near the surface layer is more serious. Adding a slope ratio is beneficial to improve the flow patterns and recirculation, while the surface vortex width increases. Additionally, with the decrease in the slope ratio, recirculation width and the ratio of recirculation to the width of the layer decrease, and the minimum values are 9.19 cm and 22.97%, respectively. However, the lower the slope ratio is, the greater recirculation inhibition affects are, and the more serious the surface vortex is. With the decrease in the slope ratio, the widest surface vortex width and the ratio of the widest surface vortex to the width of the layer increase from 6.1 to 12 cm and from 7.82 to 17.14%, respectively. This research represents an advance in lateral withdrawal and provides support for further designs.

Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear LP Turbine Cascade

End wall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modify the blade loading and overall performance in terms of stable operating range. Present study aimed to determine the end wall flow streams in a low speed low pressure linear turbine cascade vane using numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at end wall. Location of generation of horseshoe vortex streams and subsequent vortex patterns are identified in the section. The selection of suitable turbulence model among SST (Shear Stress Transport) k–ω and SST γ–θ to identify end wall flow streams is studied in prior in the section. The steady state numerical study is performed using Reynolds Averaged Navier-Stoke’s Equations closed by SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in later section. The second section includes effect of flow incidence and turbulence intensity on the end wall secondary flow field. Inflow incidences considered for the study are −20°, −10°, 0° (design incidence), +10° and +20°. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an end wall and found the change in behavior with an inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

Effects of Rotation on Transient Fluid Flow and Heat Transfer Through a Curved Square Duct: The Case of Negative Rotation

The fluid flow and heat transfer through a rotating curved duct has received much attention in recent years because of vast applications in mechanical devices. It is noticed that there occur two different types of rotations in a rotating curved duct such as positive and negative rotation. The positive rotation through the curved duct is widely investigated while the investigation on the negative rotation is rarely available. The paper investigates the influence of negative rotation for a wide range of Taylor number (−10 ≤ Tr ≤ −2500) when the duct itself rotates about the center of curvature. Due to the rotation, three types of forces including Coriolis, centrifugal, and buoyancy forces are generated. The study focuses and explains the combined effect of these forces on the fluid flow in details. First, the linear stability of the steady solution is performed. An unsteady solution is then obtained by time-evolution calculation and flow transition is determined by calculating phase space and power spectrum. When Tr is raised in the negative direction, the flow behavior shows different flow instabilities including steady-state, periodic, multi-periodic, and chaotic oscillations. Furthermore, the pattern variations of axial and secondary flow velocity and isotherms are obtained, and it is found that there is a strong interaction between the flow velocities and the isotherms. Then temperature gradients are calculated which show that the fluid mixing and the acts of secondary flow have a strong influence on heat transfer in the fluid. Diagrams of unsteady flow and vortex structure are further sketched and precisely elucidate the curvature effects on unsteady fluid flow. Finally, a comparison between the numerical and experimental data is discussed which demonstrates that both data coincide with each other.

Optimization of Sweep and Blade Lean for Diffuser to Suppress Hub Corner Vortex in Multistage Pump

The bowl diffuser is the main flow component in multistage submersible pumps; however, secondary flow fields can easily induce a separation vortex in the hub corner region of the bowl diffuser during normal operation. To explore the flow mechanism of the hub corner separation vortex and develop a method for suppressing hub corner separation vortices, the lean and sweep of the diffuser blade were optimized using computational fluid dynamics (CFD) simulations and central composite design. Diffuser efficiency, static pressure recovery coefficient, and non-uniformity were selected as the optimization objectives. Details of the internal flow were revealed and the collaborative response relationships between blade lean/sweep parameter equations and optimization objectives were established. The optimization results show that a greater pressure difference between the pressure surface and suction surface (PS–SS) at the inlet can offset transverse secondary flow, whereas a lower PS–SS pressure difference will cause a drop in low-energy fluid in the diffuser mid-section. The blade’s lean scheme suppresses the hub corner separation vortex, leading to an increase in pressure recovery and diffuser efficiency. Moreover, optimizing the sweep scheme can reduce the shroud–hub pressure difference at the inlet to offset spanwise secondary flow and enhance the hub–shroud pressure difference at the outlet, thus driving low-energy fluid further downstream. The sweep scheme suppresses the hub corner vortex, with a resulting drop in non-uniformity of 13.1%. Therefore, optimization of the diffuser blade’s lean and sweep can result in less low-energy fluid or drive it further away from hub, thereby suppressing the hub corner vortex and improving hydraulic performance. The outcomes of this work are relevant to the advanced design of bowl diffusers for multistage submersible pumps.

Evaluation of Secondary Flow between Rotating Concentric Spheres Using a Perturbation Method

A new approach to evaluate the Newtonian flow between concentric rotating spheres is introduced in this paper. A general analytic solution to the problem is deduced using a perturbation method that takes into account the primary and secondary flows produced between the spheres, as well as an alternative analytical method. In order to exemplify the results of the previous analysis, six particular cases were studied. The results of the perturbation method show that under certain circumstances the secondary flow is no negligible, as is usually considered, but it is comparable to the value of the primary one. While the analytical method allows us to simulate the flow with results very similar to those of other authors.