Parametric study of cone angle influence on bubble vortex breakdown onset in laminar conical flow at various swirl numbers

The current work studies a swirling laminar viscous pipe flow with a controllable swirl number and varying pipe divergence cone angle. Such flows are widely used in various engineering applications. When a certain level of flow swirl is reached, a phenomenon called vortex breakdown occurs, the characteristics of which depend on the intensity of swirling of the flow and the Reynolds number. However, in addition to these two parameters, an important influence is exerted by the pipe opening angle, which often does not allow generalizing the results obtained in the pipe flow with even slightly different angles. Since experimentally it is quite difficult and expensive to change the pipe angle, especially considering the water as working fluid, this issue could be solved using CFD techniques. Using the design study, 63 different combinations of S and α are considered. The effect of the pipe divergence angle on the position of the bubble vortex breakdown and its properties is demonstrated. It is shown that there is a nonlinear relationship between the position of the bubble breakdown onset and the minimum value of the axial velocity at the axis depending on the opening angle of the cone.

Computational Modeling of Voice Production Using Excised Canine Larynx

A combined experimental-numerical work was conducted to comprehensively validate a subject-specific continuum model of voice production in larynx using excised canine laryngeal experiments. The computational model is a coupling of the Navier-Stokes equations for glottal flow dynamics and a finite element model of vocal fold dynamics. The numerical simulations employed a cover-body vocal fold structure with the geometry reconstructed from MRI scans and the material properties determined through an optimization-based inverse process of experimental indentation measurement. The results showed that the simulations predicted key features of the dynamics observed in the experiments, including the skewing of the glottal flow waveform, mucosal wave propagation, continuous increase of the divergent angle and intraglottal swirl strength during glottal closing, and flow recirculation between glottal jet and vocal fold. The simulations also predicted the increase of the divergent angle, glottal jet speed and intraglottal flow swirl strength with the subglottal pressure, same as in the experiments. Quantitatively, the simulations over-predicted the frequency and jet speed and under-predicted the flow rate and divergent angle for the larynx under study. The limitations of the model and their implications were discussed.

Fuel regression rate estimation model for swirling-flow hybrid rocket engines

In the current study, an analytical model to estimate the fuel surface regression rate of hybrid rocket engines with head-end swirling flow oxidizer injection is established. The model is based on a convective heat feedback approach and, in conjunction with the corresponding boundary layer (or zone) concept which accounts for transpiration, effective hydraulic diameters, and wall friction. The effective tangential (swirl) velocity of the gas provides a positive augmentation effect to the fuel regression rate, above that due to the axial mass flux component of the core gas flow. From the literature, a variety of propellant combinations, engine sizes, and flow swirl numbers are evaluated for engines having circular-port fuel grains, with sample results provided in this report for comparative purposes. The predicted fuel regression rates for the most part compare quite well with the corresponding experimental data. Additionally, the validity of the underlying assumption of a slowly decaying effective axial and tangential velocity of the gas as one moves downstream along the central fuel port is to some degree verified using a computational approach, based on a simplified engine flow model. As a final element of the overall study, the fuel regression rate model is evaluated for parameter sensitivity. The settings for some propellant and gas properties are found to have a significant influence on the quantitative predictive results.

Fuel regression rate estimation model for swirling-flow hybrid rocket engines

In the current study, an analytical model to estimate the fuel surface regression rate of hybrid rocket engines with head-end swirling flow oxidizer injection is established. The model is based on a convective heat feedback approach and, in conjunction with the corresponding boundary layer (or zone) concept which accounts for transpiration, effective hydraulic diameters, and wall friction. The effective tangential (swirl) velocity of the gas provides a positive augmentation effect to the fuel regression rate, above that due to the axial mass flux component of the core gas flow. From the literature, a variety of propellant combinations, engine sizes, and flow swirl numbers are evaluated for engines having circular-port fuel grains, with sample results provided in this report for comparative purposes. The predicted fuel regression rates for the most part compare quite well with the corresponding experimental data. Additionally, the validity of the underlying assumption of a slowly decaying effective axial and tangential velocity of the gas as one moves downstream along the central fuel port is to some degree verified using a computational approach, based on a simplified engine flow model. As a final element of the overall study, the fuel regression rate model is evaluated for parameter sensitivity. The settings for some propellant and gas properties are found to have a significant influence on the quantitative predictive results.

COMBUSTION OF A GAS SUSPENSION OF COAL DUST IN A SWIRLING FLOW

Swirling combustion is currently one of the most important engineering problems in physics of combustion. There is a hypothesis on the increase in the combustion efficiency of reacting gas mixtures in combustion chambers with swirling flows, as well as on the increase in the efficiency of fuel combustion devices. In this paper, it is proposed to simulate a swirling flow by taking into account the angular component of the flow velocity. The aim of the study is to determine the effect of the angular component of the flow velocity on the characteristics of the flow and combustion of an air suspension of coal dust in a pipe. The problem is solved in a twodimensional axisymmetric approximation with allowance for a swirling flow. A physical and mathematical model is based on the approaches of the mechanics of multiphase reacting media. A solution method involves the arbitrary discontinuity decay algorithm. The impact of the flow swirl and the size of coal dust particles on the gas temperature distribution along the pipe is determined.

Numerical Simulation of Double Surface Liquid Ejector with Flow Swirl for Centrifugal Pump

Many systems with liquid ejectors and centrifugal pump are known. Often, jet pumps are used to provide a self-priming mode, as well as an acceptable pressure level for cavitation-free operation. The main disadvantage of such systems is the relatively low efficiency associated with the peculiarities of energy transfer in ejector. To increase efficiency double surface jet pump with driving and suction flow swirl (with circumferential component of velocity) is proposed. The active flow swirling is ensured by using of multi-nozzle tangential nozzle inlet and passive flow part by a special blade system. Combination of these factors makes it possible to improve the efficiency of energy conversion process. In comparison with the known design increases pump efficiency by 10 % – 15 %. Flow swirl also permits to reduce horizontal overall size by increasing the diffuser angle and reducing the mixing chamber length. These positive effects can be achieved by using methods and recommendations given in this paper. The paper also includes ANSYS CFX numerical simulation study results of double surface jet pump and analysis of the impact of nozzle position, length of the mixing chamber and other geometry parameters on pump performance. The results allow optimize the constructive solutions.

Effect of Cross-Flow Swirl on the Trajectory of Spray in an Annular Passage

This paper presents the experimental analysis of the impact of swirl number of cross-flowing air stream on liquid jet spray trajectory at a fixed air flow velocity of 42 m/s with the corresponding Mach number of 0.12. The experiments were conducted for 4 different swirl numbers (0, 0.2, 0.42 and 0.73) using swirl vanes at air inlet having angles of 0°, 15°, 30° and 45° respectively. Liquid to air momentum flux ratio (q) was varied from 5 to 25. High speed (@ 500 fps) images of the spray were captured and those images were processed using MATLAB to obtain the path of the spray at various momentum flux ratios. The results show interesting trends for the spray trajectory and the jet spread in swirling air flow. High swirling flows not only lead to spray with lower radial penetration due to sharp bending and disintegration of liquid jet, but also result in spray with high jet spread and spray area. Based on the results, correlations for the spray path have been proposed which incorporates the effects of the swirl number of the air flow.

Understanding How Complex Terrain Impacts Tornado Dynamics Using a Suite of High-Resolution Numerical Simulations

A simulated vortex within a large-eddy simulation is subjected to various surface terrain, implemented through the immersed boundary method, to analyze the effects of complex topography on vortex behavior. Thirty simulations, including a control with zero-height terrain, are grouped into four categories—2D sinusoidal hills, 3D hills, valleys, and ridges—with slight modifications within each category. A medium-swirl-ratio vortex is translated over shallow terrain, which is modest in size relative to the vortex core diameter and with no explicitly defined surface roughness. While domain size restricts results to the very near-field effects of terrain, vortex–terrain interaction yields notable results. Terrain influences act to increase the variability of the near-surface vortex, including a notable leftward (rightward) deflection, acceleration (deceleration), and an expansion (a contraction) of the vortex as it ascends (descends) the terrain owing to changes in the corner flow swirl ratio. Additionally, 10-m track analyses show stronger horizontal wind speeds are found 1) on upslope terrain, resulting from transient subvortices that are more intense compared to the control simulation, and 2) in between adjacent hills simultaneous with strong pressure perturbations that descend from aloft. Composite statistics confirm that the region in between adjacent hills has the strongest horizontal wind speeds, while upward motions are more intense during ascent. Overall, valley (ridge) simulations have the largest horizontal (vertically upward) wind speeds. Last, horizontal and vertical wind speeds are shown to be affected by other terrain properties such as slope steepness and two-dimensionality of the terrain.

Part 1: A Swirl Vane Generation Code for Fuel Spray Nozzles

Achieving an optimal level of flow swirl is required for efficient mixing of air and fuel in order to realise lean combustion. A novel method is devised to achieve a necessary level of swirl, using NACA airfoil profiles as the baseline for swirl stator blades. Formulas for achieving a required level of swirl have been derived and implemented in a computer program that generates aerodynamic vanes which meet the specified swirl. The usability of the program over a broad range of Reynolds numbers is verified. A curve fitting method has been developed, taking into account the trailing edge angles and blade solidity, in order to speed up the iterative process. A significant computational speed-up is achieved from this approach, and an excellent initial preliminary vane design can be obtained, which can later be introduced inside an automated optimisation process.