Investigation Of Flow Separation Research Articles

Investigation of magneto-convection characteristics in a sudden expanding channel with convex surface geometry under thermally developing flow conditions

PurposeThe purpose of this study is to analyse the magnetic field effect on Fe3O4/H2O Ferrofluid flowing in a sudden expansion tube, which has specific behaviour in terms of rheology, with convex dimple fins. Because the investigation of flow separation is a prominent application in performance, the effect of magnetic field and convex dimple on the thermo-hydraulic performance of sudden expansion tube are examined, in detail.Design/methodology/approachDuring the solution of the boundary conditions of the sudden expansion tube, finite volume method was used. Analyses have been conducted considering the single-phase solution, steady-state, incompressible fluid and no-slip condition of the wall under forced convection conditions. In the analyses, it has been assumed that the flow was developing thermally and has been fully developed hydrodynamically.FindingsThe present study focuses on exploring the influence of the magnetic field, nanofluid concentration and convex dimple fins on the thermo-hydraulic performance of sudden expansion tube. The results indicate that the strength of the magnetic field, nanofluid concentration and convex dimple fins have a positive effect on the convective heat transfer in the system.Originality/valueThe authors conducted numerical studies, determining through a literature search that no one had yet investigated enhancing heat transfer on a sudden expansion tube using combinations of magnetic fields, nanofluids and convex dimple fins. The results of the numerical analyses provide valuable information about the improvement of heat transfer and system performance in electronic device cooling and heat exchangers.

Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

INCREASE IN CONVECTIVE HEAT TRANSFER OVER A BACKWARD-FACING STEP IMMERSED IN A WATER-BASED TiO2 NANOFLUID

Investigation of flow separation and reattachment of 0.2% water-based TiO2 nanofluid in an annular suddenly expanding pipe is presented in this paper. Such flows occur in various engineering and heat transfer applications. A computational fluid dynamics package (FLUENT) is used to study turbulent nanofluid flow in this research. Only a quarter of an annular pipe was investigated and simulated because of its symmetrical geometry. Standard k–e second-order implicit, pressure based-solver equations are applied. Reynolds numbers between 17,050 and 44,545, step height ratio of 1.82, and a constant heat flux of 49,050 W/m2 were utilized in simulation. The numerical simulation results show that increase in the Reynolds number leads to an increase of the heat transfer coefficient and of the Nusselt number. Moreover, the surface temperature dropped to its lowest value after the expansion and then gradually increased along the pipe. Finally, the chaotic movement and high thermal conductivity of the TiO2 nanoparticles have contributed to the overall heat transfer enhancement of the nanofluid.

Investigation of Flow Separation in a Diffuser of a Bulb Turbine

A three-dimensional unsteady flow separation in the straight diffuser of a model bulb turbine is investigated using tuft visualizations, unsteady wall pressure sensors, and particle image velocimetry (PIV). Experimental results reveal a link between the flow separation zone extension and the sudden drop in turbine performances. The flow separation zone grows as the flow rate increases past the best efficiency operating point (OP). It starts on the bottom wall and expands azimuthally and upstream. It deviates and perturbs the flow far upstream. Despite high unsteadiness, a global separation streamline pattern composed of a saddle point and a convergence line emerges.

Computational Investigation of Flow Separation over Naca 23024 Airfoil at 6 Million Free Stream Reynolds Number

The following work is the CFD analysis of NACA 23024 airfoil. The analysis is carried out for a free stream Reynolds number of 6 million for which the wind tunnel results are available. The CFD analysis is carried out using Ansys Fluent Solver. The analysis is carried out using Spalart Allmaras turbulence model, K-omega SST turbulence model with flow transition capabilities, Standard K-Epsilon Turbulence model and K-omega SST turbulence model.It is to be noted that each turbulence model employs different mathematical approach to model boundary layer. The analysis results are then compared with the wind tunnel results and the performance of the turbulence models are discussed. This study recommends an accurate methodology to conduct CFD analysis for external aerodynamic flows.

Experimental and numerical investigation of separated flows in subsonic diffusers

The results of a special investigation of the diffuser flowfield are presented for two models of curvilinear diffuser channels with annular and rectangular cross-sections. The flow is visualized and the total pressure fields are measured by means of low-inertia transducers. At the same time, the flows are numerically calculated using commercial programs, together with codes developed by the authors. In these calculations the stationary and time-dependent Reynolds equations closed by different turbulence models, as well as the time-dependent Navier-Stokes equations, were integrated. A considerable difference between the measured data and the results of the numerical calculations in the stationary formulation is found to exist. At the same time, it has been possible to describe the occurrence of spatial inhomogeneities, the flow pattern, and the level of the experimentally observed aerodynamic losses on the basis of the solution of time-dependent problems.

Experimental and numerical investigation of flow separation in a supersonic nozzle

The flow in a two-dimensional symmetric convergent-divergent supersonic nozzle with and without a deflector at the exit plane was tested experimentally and numerically. Combined optoelectronic devices were used to demonstrate the possibilities of the shadow and schlieren methods and holographic interferometry for the flow visualization especially in the separation region. A series of experiments was performed in a trisonic wind tunnel (VTI, Beograd). The experimental results obtained using optical methods are compared with the pressure measurements and numerical calculations. Numerical results were obtained using a code for solving the average Navier-Stokes equations. Five structured meshes with different resolutions and two turbulent models were employed. The coupled influence of the mesh resolution and the order of accuracy of the used numerical scheme is analyzed.

Investigation of flow separation on a finite span wing by Liquid Crystal Coatings

Investigation of flow separation on a finite span wing by Liquid Crystal Coatings

Investigation of Separated Flow Around a Curved Air Intake

This paper presents an investigation of two-dimensional separated flow in and around a submerged curved intake by experiment and computation. The elliptic Navier-Stokes equations are employed which are discreted in body-fitted coordinate system by the SIMPLE method. The results show that the flow separation exists near and behind the inlet and the duct flow is distorted. Comparison between the computational and experimental data is fairly satisfactory.

Investigation of separated flow around a curved air intake

This paper presents an investigation of two-dimensional separated flow in and around a submerged curved intake by experiment and computation. The elliptic Navier-Stokes equations are employed which are discreted in body-fitted coordinate system by the SIMPLE method. The results show that the flow separation exists near and behind the inlet and the duct flow is distorted. Comparison between the computational and experimental data is fairly satisfactory.

Study of flow separation and reattachment due to backward step

ABSTRACT Investigation of flow separation produced by a single backward facing step placed in a two-dimensional channel for turbulent flow of air was performed. Experiments were performed in two different conditions – flow without backward step (undisturbed flow) and flow with backward step (disturbed flow). The mean velocity profiles in the undisturbed flow were measured and different characteristic lengths were determined and hence the fully developed turbulent boundary layer was attained. A plate was then fixed at the bottom of the tunnel. So that a region of separation flow was created. Monitoring of the velocity at the same grid points showed that the profiles were vigorously distorted giving rise to positive wake effect. The separation length increased with the increase of Reynolds number and the results agree well with other authors.

Investigation of flow separation on a supercritical airfoil

Transonic shock/boundary-layer interaction on the upper surface of a supercritical airfoil was investigated in the National Aeronautical Establishment High Reynolds Number Two-Dimensional Test Facility. Skin-friction coefficient measurements on the airfoil surface were carried out using a Preston tube. At the lower Mach number range of the experiments, shock-induced and trailing-edge separation regions were found to exist simultaneously. Detailed experimental measurements were carried out at M = 0.688 and various values of a to investigate the merging of the two separated-flow regions. Steady and unsteady pressure measurements were made for various types of shock/boundary-layer interaction. Pressure power spectra were computed to study the characteristics of pressure fluctuations in the separated-flow regions. Fluctuating normal forces were measured for different types of flow separation, and the behavior of the unsteady load experienced by the airfoil was presented. Broadband cross-correlations of the pressure field were carried out to determine the convection velocities for attached and separated flows.

Investigation of separated flow behind two-dimensional and three-dimensional bodies acted on by a spherical shock wave

Investigation of separated flow behind two-dimensional and three-dimensional bodies acted on by a spherical shock wave

A Numerical Investigation of Flow Separation over Moving Walls

Two-dimensional, steady, incompressible, laminar boundary-layer flows over moving walls are numerically investigated with special regard to the MRS criterion for flow separation. Flows are analysed by using approximate equations which allow pressure variation in the direction normal to the wall. Solutions are obtained through regions of separation bubbles, with prescribed external velocity distributions, both for the case of upstream moving walls and for the case of downstream moving walls. Solutions for the case of upstream moving walls are obtained for the first time. Flow properties over moving walls are discussed concerning the MRS criterion.

Comment on 'Lower bounds on deformations of dynamically loaded rigid-plastic continua.'

In general, a three-dimensional shock wave-boundary layer interaction can be viewed locally as a two-dimensional one with cross flow and mass transfer—a result of the scavenging vortex in the three-dimensional case. This interpretation is supported by experimental evidence which shows that the extent of a separated flow region is considerably greater for laminar than for turbulent flow for three-dimensional shock-wave/boundarylayer interaction as well as for the two-dimensional case. Thus, in retrospect, it is reasonable to expect a sharp change in the flow separation line as a skewed impinging shock crosses a region of boundary-layer transition. Conversely, a sharp change in an otherwise smoothly curved separation line on a planar surface is most likely indicative of transition because, in the absence of other disturbances in a flow, there is no physical mechanism whereby a shock generator of simple geometry should produce a distorted separation line. References 1 Korkegi, R. H., Survey of Viscous Interactions Associated with High Mach Number Flight, AIAA Journal, Vol. 9, No. May 1971, pp. 771-784. 2 Young, F. L., Kaufman, L. G., II, Korkegi, R. H., Experimental Investigation of Interactions between Blunt Fin Shock Waves and Adjacent Boundary Layers at Mach Numbers 3 and 5, ARL 68-0214, Dec. 1968, Aerospace Research Labs., Wright-Patterson Air Force Base, Ohio. 3 West, J. E. and Korkegi, R. H., Interaction in the Corner of Intersecting Wedges at a Mach Number of 3 and High Reynolds Numbers, ARL 71-0241, Oct. 1971, Aerospace Research Labs., Wright-Patterson Air Force Base, Ohio; also AIAA Paper 72-6, San Diego, Calif., 1972. 4 Kaufman, L. G. II, Meckler, L., and Hartofilis, S. A., An Investigation of Flow Separation on Aerodynamic Controls at Hypersonic Speeds, Journal of Aircraft, Vol. 3, No. 6, Nov.-Dec. 1966, pp. 555-561.

Investigation of flow separation over a rearward-facing step in a hypersonic stream.

Investigation of flow separation over a rearward-facing step in a hypersonic stream.

An investigation of flow separation and aerodynamic controls at hypersonic speeds.

An investigation of flow separation and aerodynamic controls at hypersonic speeds.