Effect of Rotational Speed Variation on the Flow Characteristics in the Rotor-Stator System Cavity

In this paper, to study the effect of dynamic and static interference of clearance flow in fluid machinery caused by changes in rotational speed, the model was simplified to a rotor-stator system cavity flow. Investigating the flow characteristics in the cavity by changing the rotor speed of the rotor-stator system is of considerable significance. ANSYS-CFX was applied to numerically simulate the test model and the results were compared with the experimental results of the windage torque of the rotor-stator system. The inlet flow rate and geometric model remained unchanged. With an increase in the rotating Reynolds number, the shear stress on the rotor wall gradually increased, and the maximum gradient was within l* < 0.15. In addition to the shear stress, the tangential Reynolds stress Rrθ contributed partly to the torque on the rotor wall. The swirling vortex formed by entrainment in the cavity of the rotor-stator system tended to separate at ReΦ= 3.53 × 106. As the rotating Reynolds number continued to increase, the secondary vortex finally separated completely. The strength of the vortex in the rotor turbulent boundary layer decreased with an increase in the rotating speed, but the number of vortex cores increased with the increase of speed. Depending on the application of the fluid machine, controlling the rotating speed within a reasonable range can effectively improve the characteristics of the clearance flow.

Characterization of the airflow field in the rotor spinning unit based on a novel experimental approach and numerical simulation

It is very challenging to experimentally characterize and verify the airflow in the rotor spinning machine because the process takes place in an enclosure. In an attempt to portray the process, we present a methodology that combines a novel experimental approach and numerical techniques. We developed a model unit and used colored smoke to mimic the airflow behavior practically, measured the air pressure, and compared the results to the simulation data. Three state conditions, namely suction and rotation (the regular rotor spinning operation, (Case 1)), without rotation (Case 2), and without suction (Case 3), were adopted to investigate the formation mechanism of the airflow field in the rotor spinning unit based on two operating conditions. Results show that, in a regular state, the airstream accelerates rapidly in the transfer channel under the dominant action of air suction at the rotor outlet and crashes clockwise to the rotor wall with the joint action of two operating conditions. In the rotor, the airflow flows clockwise with the velocity distribution of a multi-ring gradient due to the dominant action of high-speed rotor rotation. Analytics from the air pressure indicate that while the air pressure in the rotor is mainly controlled by the action of the air suction mechanism, it is also affected by the superposition action of the rotation mechanism. This approach is groundbreaking for rotor spinning machine optimization and is anticipated to trigger more insights that will lead to fundamental research in the spinning industry and beyond.

Coupling of inverse method and cuckoo search algorithm for multiobjective optimization design of an axial flow pump

This work describes the application of a multiobjective cuckoo search method for turbomachinery design optimization of an axial pump. Maximization of the total efficiency and minimization of the required net positive suction head of the pump are the two objective functions considered for the optimization problem. The optimization process is carried out on a range of imposed volumetric flow rates, with taking into account at each discretized radius between the hub and tip of the rotor: the profile camber, rotor wall thickness, angular deviation, and the solidity, regarded as geometrical constraints and nominal flow rate as mechanical constraint. Two strategies are proposed in order to solve the problem. In the first one, three forms of mono-objective model with two variables, total efficiency and net positive suction head, are considered. In the second one, a multiobjective model with nondominated sorting scheme is adopted. A comparative evaluation of results obtained from the proposed approach with those of a reference machine and genetic algorithm allowed us to validate the present work.

Effects of Gas-Ingestion Through Turbine Rim Seals on Flow and Heat Transfer in the Wheel-Space

This paper presents numerical simulations of the gas-ingress into turbine wheel-space through the rim seal. The objective is to reveal the physical mechanism of gas-ingress flow in the wheel-space and its effects on the heat transfer in the cavity. Firstly, the wheel-space without mainstream passage is simulated to get the baseline of the case without ingress, and the windage heat in the cavity is investigated. Secondly, the gas-ingestion is conducted, and its effects on the flow and heat transfer in the wheel-space are studied. The results reveal that in the absence of ingress into the wheel-space, the windage heating pays an important contribution to the stator/rotor temperatures because of the high rotational speed of the engine. When ingress occurs, the ingested gas mixes with the sealing air at the seal clearance and then inward flows into the wheel-space along the stator wall, and thus leads to the stator wall heated. The rotor wall is relatively less heated by the invaded gas than the stator wall because of the thermal buffering of the sealing air on the rotor wall. The thermal buffer ratio, which is defined as the ratio of the sealing effectiveness on the stator wall to that on the rotor wall, is shown dependent on the sealing flow rate. It is increased as the sealing flow rate increases.

Design of a Machine by Low Cost and the High Performance for Produced Powder Materials

Mechanical alloying and mechanical fine grinding processes are mostly based on the high energy milling technique. Equipment of a horizontal high-energy ball mill that has been developed in the Cefet-BA is a low cost machine with high performance. These milling machines are equipped with a cylindrical stainless steel horizontal container. Inside the container, a chamber of water circulation is used to maintain, powdered materials, the room temperature. The grinding container inside to chamber horizontal container is a container, cylindrical stainless steel, opened of the two sides. The container with the powder particles is a sealed of two sides and vacuum out-gassed is realized. A motor driven rotor is used to accelerate the grinding media and the milling process is realized due to the ball to ball/rotor/wall impacts as their kinetic energy is transferred into the powder which is randomly located between the colliding balls. The rotor milling machine equipment permits two rpm e.g. 500 and 1500 rpm. Machines based on this design from lab scale (3.0 liter volume), mainly to develop new powders and materials.

A Non-Coupled CFD-FE Procedure to Evaluate Windage and Heat Transfer in Rotor-Stator Cavities

A combined CFD and FE method, which could be applied to a wide range of internal air system rotor-stator cavities and which overcomes the disadvantages of many non-coupled approaches, is presented. It is used to predict windage and heat transfer in the HP compressor rear cone outer cavity of a service aeroengine. From the CFD it is shown that rotor wall torque, and hence windage, decreases as cavity throughflow increases, and that the data from several engine cavities can be reduced to a single characteristic of windage versus mass flow. Stator wall torque is also presented. A comparison with engine thermocouple data shows that further development of the modelling is required before engine testing could be replaced.

Flow Structures Inside a Rotor-Stator Cavity

This paper describes an experimental investigation initiated to determine the threedimensional flow field inside the rim seal cavity of a double-shrouded rotor-stator system. Thereby, the effects caused by perturbances in the rotor wall were additionally examined. The objective of this work is to provide detailed information about the mechanisms that can promote elevated temperature levels in the high pressure section of a gas turbine. Both ingested hot gas and windage heating generated at the rotor-stator interface can severely affect the material temperatures and thus considerably increase the thermal load of the rotating parts.The flow velocities were measured by means of an advanced LDV system capable of providing phase-resolved data. The flow field was determined for two different rotorstator combinations. One of the rotor disks contained small rectangular cavities, located at the disk rim and arranged uniformly in’ the circumferential direction. These elements are referred to as the shank cavities of the rotor disk.The mechanical torque was measured to demonstrate the influence of these elements on the windage power. The measurements were performed at operating conditions that are typical for aero-engines. It is shown that a perturbed rotor surface can raise the drag notably. The experiments were conducted in a high speed test rig at rotational Reynolds numbers up toReϕ≈4.2*106. The data were plotted as the dimensionless moment coefficientcMand correlated withReϕand the dimensionless cooling flow ratecw.

A Numerical Investigation of Premixed Combustion in Wave Rotors

Wave rotor cycles that utilize premixed combustion processes within the passages are examined numerically using a one-dimensional CFD-based simulation. Internal-combustion wave rotors are envisioned for use as pressure-gain combustors in gas turbine engines. The simulation methodology is described, including a presentation of the assumed governing equations for the flow and reaction in the channels, the numerical integration method used, and the modeling of external components such as recirculation ducts. A number of cycle simulations are then presented that illustrate both turbulent-deflagration and detonation modes of combustion. Estimates of performance and rotor wall temperatures for the various cycles are made, and the advantages and disadvantages of each are discussed.

A Numerical Investigation of Premixed Combustion in Wave Rotors

Wave rotor cycles which utilize premixed combustion processes within the passages are examined numerically using a one-dimensional CFD-based simulation. Internal-combustion wave rotors are envisioned for use as pressure-gain combustors in gas turbine engines. The simulation methodology is described, including a presentation of the assumed governing equations for the flow and reaction in the channels, the numerical integration method used, and the modeling of external components such as recirculation ducts. A number of cycle simulations are then presented which illustrate both turbulent-deflagration and detonation modes of combustion. Estimates of performance and rotor wall temperatures for the various cycles are made, and the advantages and disadvantages of each are discussed.