Introduction to the problem of calculating the parameters of the mixing chamber of an afterburning bypass engine

The article considers the problem of calculation accuracy when using mathematical models of gas-turbine engines of the second level of complexity, using the example of a device for mixing the flows of the core engine and the bypass duct of a gas turbine engine, and suggests methods for solving it. The processes taking place in mixing chambers of air-breather engines are considered to be difficult for mathematical modeling since the exchange of kinetic and thermal energies of the flows characterized by different velocities, pressures, temperatures and chemical composition occurs in them simultaneously. The mixer does not only ensure mixing of flows from different engine ducts, but also acts as a kind of throttle. It regulates the pressure downstream of the fan and, consequently, air consumption in the bypass duct, thus affecting directly the fan characteristics and the distribution of flows over the engine ducts. The paper presents the dependencies of the workflow parameters that allow for more accurate verification of mixer models of the second level of complexity.

Mixing in the NETmix Reactor

NETmix is a static mixing reactor composed of a network of mixing chambers interconnected by channels. The repetitive mixing pattern inside the reactor enables the use of reduced geometries to represent the NETmix network, such as the ExtendedNUB model, used in this work. Mixing in NETmix is based on the impingement of jets, issuing from channels. Inside the chambers, the jets are engulfed by dynamic vortices which can be quantified using Lagrangian techniques. Batch Lagrangian Mixing Simulation (BLMS) is based on successive injections of particles to measure the fraction of the fluids at the outlet of the mixing chambers. The distribution of the outlet fraction of particles indicates that it is possible to have nearly perfect mixing inside the NETmix chambers, depending on the dimensions of the channels and chambers. The NETmix design is here optimized in relation to the chamber diameter to channel width ratio, D/d. Results from BLMS show that best performance in NETmix occurs for 6.65≤D/d≤6.85.

Development of a polyurea-based composition with an extended life span

Objectives. Improvement of the technology for obtaining polymer-sprayed coatings based on polycarbodiimides (polyureas) with high chemical, hydrolytic, and abrasive resistance and improved physical and mechanical properties, as well as obtainment of polyurea compositions with a lifetime of at least 5 min without loss performance characteristics (i.e., “hand-applied” polyureas) suitable for repair of coatings already in use.Methods. The reaction rate between isocyanate and amino groups is almost a hundred times higher than that between isocyanate and hydroxyl groups, necessitating the use of special highperformance and high-pressure installations equipped with self-cleaning mixing chambers and heating of components. The following are determined from the obtained materials: strength, elongation at break according to the standard method, Taber abrasion, and Shore hardness.Results. Three methods of slowing down the reaction are investigated: 1) the synthesis of prepolymers with the content of NCO groups from 10.5% to 18%; 2) the addition of a plasticizer into the prepolymer in the amount of 1–10 mass parts; and 3) the introduction of polyesters into the composition and radiation of the so-called “hybrid” systems. When using 14% polyesters with a molecular weight of 2000 Da, only “hybrid” systems make it possible to obtain compositions with a lifetime of more than 5 min. At the same time, the tensile strength decreases by 20%, and the abrasion increases by 40%; however, such “hybrid” systems have a higher adhesion force and are cheaper than pure polyureas, allowing them to be used as “repair” systems.Conclusions. The developed composition and technology of applying “hybrid” systems allow for the repair of existing coatings without using specialized devices. “Manual” polyurea is easy to use and does not require special training.

Design optimization of micromixer with circular mixing chambers (M-CMC) using Taguchi-based grey relational analysis

The aim of the present study is to optimize the micromixer with circular mixing chambers (M-CMC) using Taguchi-based grey relational analysis approach. Simulations are performed to investigate the effect of design parameters viz. chamber diameter, transverse offset and width of constriction channel on performance characteristics for parameter sets corresponding to Orthogonal Array (OA) L9. Further, grey relational grade is used to identify the optimal set of design parameters. In depth study of flow and mixing dynamics are carried out to visualize the mixing mechanism for optimal and other two cases of proposed micromixer design configuration for Re in the range from 0.1 to 50. In order to assess the response of each design variable at each level, analysis of variance (ANOVA) is also performed to analyse influence of design parameters on mixing index and pressure drop.

CFD Analysis of Flow Structures in a Mixing Chamber

Special mixing chambers are usually used to perform scientific experiments or for routine industrial production processes. This is the case, typically, of fan mixers in a baffled tank. Mixing chambers comprise, among other alternative elements, two counter-rotating fans at the bottom and top. These will eventually allow a mixing effect on the chamber with an adequate level of uniformity. Herein a computational flow simulation is performed for the mixing conditions of air and SO2 inside the chamber used in the CLOUD experiment, by studying in detail the flow structures and uniformity inside the chamber. This Unsteady Navier-Stokes computation is performed using the kω-SST and SAS turbulence models. A first validation step is performed by using an experimental test case, comprising a T-junction geometry, that performs the mixing of air and N2. Following this validation step a detailed analysis of the flow structures inside the 3D chamber is conducted, and specific insights are given regarding the flow uniformity. A detailed analysis of the computed mixing flow structures for the SST and SAS turbulence models is also described. It is shown that the SAS model captures with more detail the macro and meso-mmixing process with an accuracy of, at most, 6%. This value can be further reduced to values around 2% by resorting to high density meshes, with the associated computational burden.

Numerical Study of Counter Jet Formed by Impinging Jets in Cross-Flow and its Effect on Mixing

In this paper we will numerically analyse flow mixing in multiple jets in a crossflow. The system comprises a row of six radially-distributed injectors around the main pipe. The configuration represents mixing zones in industrial systems where a counter jet can be formed in the injection plane. Flow mixing can be modified as a result of geometry and injection velocities. We propose a simple model to describe the counter jet length as a function of injection flow characteristics. We also develop empirical laws to help engineers design practical test facilities. We then vary the velocity ratio to obtain both impinging and non-impinging jets in the injection plane. The focus is mainly on flow characteristics around the radial injection plane in the case of impinging jets, examining the mixing quality and efficiency by introducing a passive scalar discharge in a nitrogen flow. The mean velocity and width of the counter jet are finally analyzed by changing the injection velocities. These results are compared to those of non-impinging jets. It is found that the non-impinging jet configurations are convenient for short length mixing chambers, while the impinging ones should be considered in the case of longer mixing chambers.