Unsteady Swirling Flow Research Articles

Computation of Unsteady Swirling Flows in Nozzles and Pipes by Applying a New Locally Implicit Godunov-Type Scheme

Computation of Unsteady Swirling Flows in Nozzles and Pipes by Applying a New Locally Implicit Godunov-Type Scheme

Swirling flow analysis of Eyring–Powell fluid between coaxial disks with variable property

Abstract The main objective of this study is to examine an unsteady swirling flow of a non-Newtonian Eyring–Powell fluid between two coaxial disks. The lower and upper disks are considered to rotate with different angular velocities. The three-dimensional axisymmetric flow phenomenon and heat transfer mechanism are observed with the consequences of the magnetic field and variable thermal conductivity of the fluid. The variable thermal conductivity is taken to be dependent on the fluid temperature. The implementation of the Von Karman similarity transformations on the constituting equations of the flow phenomenon yields the dimensionless system of the non-linear equations. An optimal homotopy analysis technique is adopted to obtain analytical solutions for highly non-linear equations. In view of the same and opposite directions of disks rotation, the various aspects of the flow system corresponding to the pertinent parameters are discussed with physical significance. The obtained results indicate that both radial and axial fields are the escalating functions of the Eyring–Powell fluid parameter. Moreover, the heat transfer rate enhances with the improving variable thermal conductivity parameter.

Unsteady Turbulent Swirling Flows in a Thick Torus

Experimental study of unsteady swirling flows generated by special diverters in closed toroidal channels with different curvatures was carried out. The formation of a swirling flow in a toroidal channel is crucially different from the case of a straight cylindrical channel. It essentially depends on the curvature and is hindered by its increasing. The complex dynamics of swirling flow tightly connects with the interaction of jets after the diverter. Measurements of flow velocity using tracer’s tracks showed that the evolution of the toroidal component in torus with one diverter can be divided into two-time intervals with different power laws. The evolution of the poloidal component is rather characterized by one slope “-2/3”.

Correction to: “Computational Analysis of Unsteady Swirling Flow Around a Decelerating Rotating Porous Disk in Nanofluid” by Talat Rafiq and M. Mustafa, Arabian J. Sci. & Eng. 45 (2020) 1143–1154

Correction to: “Computational Analysis of Unsteady Swirling Flow Around a Decelerating Rotating Porous Disk in Nanofluid” by Talat Rafiq and M. Mustafa, Arabian J. Sci. & Eng. 45 (2020) 1143–1154

Computational Analysis of Unsteady Swirling Flow Around a Decelerating Rotating Porous Disk in Nanofluid

Here, we analyze the unsteady nanofluid flow triggered around a decelerating (permeable) rotating disk immersed in an otherwise calm environment. The present model assumes that disk angular velocity follows inversely linear time dependency. By following a similarity approach, the distributions of velocity and thermal fields above the disk are estimated numerically for six nanoparticle materials, namely Ag, Cu, CuO, Fe3O4, TiO2 and Al2O3. The solutions involve a dimensionless parameter $$S$$ measuring the decay rate of the disk angular velocity. We primarily focus on how solid volume fraction affects the key physical attributes, namely resisting torque, volumetric flow rate and cooling rate when unsteady action of the disk is present. Similar to pure fluid flow, there exists a critical unsteady parameter $$S = S^{*}$$ which corresponds to the free disk requiring no torque. For some range of $$S$$ , flow field surrounding the disk revolves faster than the disk itself. Similar to the steady-state case, suction seems to contribute vitally toward heat transfer enhancement of nanoparticle working fluid. Radial and circular motions around the disk diminish, and axial velocity becomes uniform when disk is subjected to sufficient amount of suction.

Large eddy simulation study of flow field characteristics of a combustor with two coaxial swirlers

The cold and reaction flow fields of a combustor with two coaxial swirlers are investigated by means of large eddy simulation. Effective data processing methods such as proper orthogonal decomposition and fast Fourier transform are employed for analysis. The complex flow phenomena such as swirling jet, shear layer, recirculation zone, and precession vortex core are observed and their characteristics are analyzed. The dynamics of the flame and its interactions with the complex swirling flows and large-scale eddies are characterized. The precession vortex core structures and its influences on the combustion process are emphatically explored. It is found that the outer shear layer produces spiral precession vortex core cantilever structures and the change of structural characteristics of the PVC determines the pressure pulsation frequency of the combustor. The results also indicate precession vortex core accelerates the mixing of unburned and burned mixture, leading to the ignition. The principal structures are studied by determining the highest energy modes via proper orthogonal decomposition. The modes are classified according to energy size. By means of proper orthogonal decomposition four-decomposition method, the vortexes of different energy and scales in swirling flow field are classified and analyzed in detail, the flow field is reconstructed, and the large-scale coherent structures and small energy flow structures are obtained. A spectral map of the turbulent kinetic energy density exhibits the −5/3 slope given by the Kolmogorov–Obukhov law. Based on the analysis of the vortex structures and their evolution, and the analysis of the transports and distributions of flow field characteristic parameters, a novel unsteady swirling flow combustion organization mechanism is proposed. It is found that combustion mainly occurs in low-energy small-scale vortexes, releasing a large amount of heat. High-temperature gas enters the recirculation zone and continues to provide energy for the precession vortex cores.

Investigation of the BulbT conical diffuser flow dynamics with TR-PIV and pressure measurements

The three dimensional unsteady swirling flow inside the draft tube of a bulb turbine is investigated using time-resolved stereoscopic particle image velocimetry. The measurement plane located inside the conical diffuser, together with synchronous pressure measurements from thirteen sensors distributed across the draft tube, allow to link the draft tube flow dynamics to a known efficiency drop of the turbine. This paper presents the experimental setup and the first observations based on statistical analyses and instantaneous snapshots of the velocity field. After the efficiency drop, the intermittency and skewness of the draft tube pressure recovery are found to be reflected onto the velocity fields. Spectral analysis reveals the presence of a coherent and non-axisymmetric structure that rotates at the same frequency as the runner, but in the opposite direction.

Modeling of atomization and distribution of drop-liquid fuel in unsteady swirling flows in a combustion chamber and free space

Numerical and experimental research of atomization and propagation of drop-liquid phase in swirling flow behind the frontal device of combustion chamber was performed. Numerical procedure was based on steady and unsteady Reynolds equations solution. It's shown that better agreement with experimental data could be obtained with unsteady approach. Fractional time step method was implemented to solve Reynolds equations. Models of primary and secondary breakup of liquid fuel jet in swirling flows are formulated and tested. Typical mean sizes of fuel droplets for base operational regime of swirling device and combustion chamber were calculated. Comparison of main features of internal swirling flow in combustion chamber with unbounded swirling flow was made.

Heat transfer simulation of unsteady swirling flow in a vortex tube

Effectiveness of not-adiabatic vortex tube application in the cooling systems of gas turbine blades depends on characteristics of swirling flows formed in the energy separation chamber. An analysis of the flow structure in the vortex tube channels has shown a presence of a complex three-dimensional spiral vortex, formed under relatively high turbulence intensity and vortex core precession. This indicates the presence of a significant unsteady flow in the energy separation chamber of the vortex tube that has a great influence on convective heat transfer of the swirling flow to the inner surface of tube. The paper contains the results of investigation of gas dynamics and heat transfer in the vortex tube taking into account the flow unsteadiness.

Suppression of unsteady swirl flow in the draft tube of a Francis hydro turbine model using J-Groove

The pressure fluctuations of the turbines are caused by the swirl component in the draft tube, which is an undesired phenomenon that needs to be improved when the turbine operates in the off-design condition. In order to avoid these kinds of unsteady flow phenomena, a technology of J-Groove on the draft tube wall is investigated by numerical method. The validation test of performance is conducted to compare the result of numerical and experimental methods. The steady and unsteady state analyses are conducted to investigate the internal flow of a Francis hydro turbine model draft tube with and without J-Groove. The swirl flow in the draft tube is significantly suppressed by the J-Groove installation. Moreover, according to the unsteady state analysis, the amplitude of pressure fluctuation in the draft tube is reduced effectively by the J-Groove.

Fuel atomization and mixing in unsteady swirling flows behind the gas-dynamic stabilizer

Features of fuel atomization and propagation in the flow behind a gas-dynamic stabilizer are considered. Estimations of the influence of transverse jets impulse magnitude on characteristics of mixing behind the stabilizer are obtained by numerical and experimental methods.

Study of phase distribution in pipe cyclonic compact separator using wire mesh sensor

Separation of gas–liquid mixture, which is achieved by using either large gravity separators or compact separators is a common and vital operation in the petroleum industry. Where space and cost are key project considerations, gas–liquid compact separators are very attractive because of their versatility and cost effectiveness. Efficient performance of the cyclonic separator depends on smooth and steady swirling flow. Unsteady swirling flow in the separator may be due to capacity constraint, improper design or unforeseen flow instability at the inlet. An understanding of phase distribution in gas discharge section of these separators would help design engineers make a better decision when selecting and sizing inlet nozzle, diameter and length of the separator. In this paper, the structure of phase distribution and liquid holdup in the gas discharge section of the separator was obtained using a 24x24 resolution wire mesh sensor (WMS). The acquired area average liquid holdup and the images were analysed using time series and 2D slice to discriminate between partial separation and critical separation condition.The liquid holdup as a function of separator inlet superficial velocity was quantified.

Investigation of a High Head Francis Turbine at Runaway Operating Conditions

Hydraulic turbines exhibit total load rejection during operation because of high fluctuations in the grid parameters. The generator reaches no-load instantly. Consequently, the turbine runner accelerates to high speed, runaway speed, in seconds. Under common conditions, stable runaway is only reached if after a load rejection, the control and protection mechanisms both fail and the guide vanes cannot be closed. The runner life is affected by the high amplitude pressure loading at the runaway speed. A model Francis turbine was used to investigate the consequences at the runaway condition. Measurements and simulations were performed at three operating points. The numerical simulations were performed using standard k-ε, k-ω shear stress transport (SST) and scale-adaptive simulation (SAS) models. A total of 12.8 million hexahedral mesh elements were created in the complete turbine, from the spiral casing inlet to the draft tube outlet. The experimental and numerical analysis showed that the runner was subjected to an unsteady pressure loading up to three-times the pressure loading observed at the best efficiency point. Investigates of unsteady pressure pulsations at the vaneless space, runner and draft tube are discussed in the paper. Further, unsteady swirling flow in the blade passages was observed that was rotating at a frequency of 4.8-times the runaway runner angular speed. Apart from the unsteady pressure loading, the development pattern of the swirling flow in the runner is discussed in the paper.

Free surface due to a flow driven by a rotating disk inside a vertical cylindrical tank: Axisymmetric configuration

The flow driven by a rotating disk at the bottom of an open fixed cylindrical cavity is studied numerically and experimentally. The steady axisymmetric Navier-Stokes equations projected onto a curvilinear coordinate system are solved by a Newton-Raphson algorithm. The free surface shape is computed by an iterative process in order to satisfy a zero normal stress balance at the interface. In previous studies, regarding the free surface deflection, there is a significant disagreement between a first-order approximation [M. Piva and E. Meiburg, “Steady axisymmetric flow in an open cylindrical container with a partially rotating bottom wall,” Phys. Fluids 17, 063603 (2005)] and a full numerical simulation [R. Bouffanais and D. Lo Jacono, “Unsteady transitional swirling flow in the presence of a moving free surface,” Phys. Fluids 21, 064107 (2009)]. For a small deflection, the first-order approximation matches with our numerical simulation and for a large deflection a good agreement is found with experimental measurements.

Test case of 3d unsteady swirling flows modeling using commercial and in-house codes

The paper gives the comparison of the results of turbulent flow computational modeling in an experimental rig using various software environments: commercial ANSYS CFX software and original Higher-Order Accuracy Codes. The effects of turbulence models and computational grid size on the computation data are evaluated.

FEM analysis of magnetorheological fluid seal of circular cooler and its experimental research

Magnetorheological fluid (MRF) exhibits drastic changes in rheological properties adjustable and controllable yield stress under external magnetic field. Based on its specialty, the MRF seal technique is proposed to deal with the air leakage of circular cooler to improve the energy efficiency for the steel industry. MRF is regarded as Bingham fluid with its magnetization vector and magnetic force expressed by mathematical functions. The FEM analysis results show that, under magnetic field, MRF which presents good pressure resistance as a result of its yield stress is in a dynamic equilibrium state in non-magnetic seal groove even with pressure difference, and due to the volume force, it presents unsteady swirl flow obviously at the right- angle edges of the two permanent magnets nearby non-magnetic separator, whereas, due to pressure difference, it shows an obvious flow without magnetic field. In the meantime, according to the experiment, it indicates that the air leakage of circular cooler is solvable effectively with the MRF seal method, and it is also proved that MRF shows controllable yield stress under magnetic field.

Study of Unsteady Swirling Flow in a Hydrodynamic Vortex Chamber

Study of Unsteady Swirling Flow in a Hydrodynamic Vortex Chamber

Numerical Simulation of Magnetic Fluid Used in Sintering and Cooling Equipments Seals as a Functional Material

Magnetic fluid as a functional material can produce volume force under external magnetic field, for the purpose of controlling the magnetic fluid flow state in the non-magnetic sealing groove with external magnetic field, the volume force is written as a function form of AZ to do with the numerical simulation of magnetic fluid flow in the sealing groove. The result shows that the magnetic fluid which distributes at the right-angle edges of the two permanent magnets nearby the separator presents unsteady swirl flow due to the volume force, while the rest magnetic fluid is in the quiescent state. It means that the magnetic fluid seal method can effectively solve the air leakage of band sintering machine and circular cooling machine.

Unsteady Swirling Flows Arising in Straight Tubes

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.

A model of unsteady swirl flow for calculation of gas exchange in piston internal combustion engines

A model of an unsteady gas mixture flow in the gas-air flow duct and a method for the numerical solution of the model equations are presented; the flow in this case being considered in one-dimensional approximation with regard to swirling. The calculation of processes in the gas-air flow duct with the use of this model makes it possible to evaluate the magnitude of charge swirling in the ICE combustion chamber and interpret the data of experiments performed on the engine equipped with a flow swirl generating injection system.