Multiblock Computational Technologies Research Articles

Anomalous intensification of vortex heat transfer in the case of separated air flow over an inclined groove in a hot isothermal region of a flat plate

Anomalous heat transfer intensification in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45°to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 103to 3×104. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3×104. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) ×103.

Low-Reynolds Mathematical Modeling of the Structure of Vortex Zones Between Periodic Surface-Located Flow Turbulators of Semicircular Cross-Section in Pipes

Mathematical modeling of the structure of vortex zones between periodic surface-located flow turbulators of a semicircular and square cross-section is carried out on the basis of multi-block computational technologies based on the solution of the factorized finite-volume method of the Reynolds equations (closed with the help of the Menter shear stress transfer mode) and the energy equation (on different-scale intersecting structured grids). This method was previously successfully applied and verified by experiment. An exhaustive analysis of the corresponding streamlines is presented, proving the advantage of abruded turbulators.

Vortex Intensification of Heat Transfer in Channels and Pipes with Periodic Elements of Discrete Roughness

A complex numerical investigation of vortex intensification of heat transfer in turbulent inhomogeneous medium flow in channels and pipes with periodic elements of discrete roughness has been carried out with the use of multiblock computational technologies, realized in a specialized package VP2/3, and of a modified model of transfer of shear stresses. As roughness elements use was made of asperities and grooves of different geometries, with air and transformer oil used as a working medium. The influence of the geometrical parameters of the indicated channels and pipes as well as of the regime parameters of the flow in them on their thermal and hydraulic efficiency has been analyzed in detail.

Intensification of Heat Exchange in Laminar Vortex Air Flow in a Narrow Channel with a Row of Inclined Oval Trenches

With the use of multiblock computational technologies, the laminar flow and heat exchange in the modules arranged in a row at regular intervals in a plane-parallel channel, at the centers of which oval trenches oriented at an angle of 45o to the flow are positioned, were calculated at Re = 103. On the basis of the calculation data obtained, it was established that an increase in the maximum velocity of the flow in such a channel by one and a half times leads to the intensification of the heat exchange in it and an increase in the heat transfer from the surface region on its wall with an inclined trench by 80% with an increase in the hydraulic losses by 25%, as compared to those of an analogous smooth channel.

Controlling the Flow past a Semicircular Airfoil at Zero Angle of Attack Using Slot Suction in One or Two Vortex Cells for Attaining Extremal Lift

Calculations using multiblock computational technologies and a model of shear-stress transport modified with allowance for the curvature of streamlines in turbulent airflow were performed at a zero angle of attack for a semicircular airfoil containing one or two surface vortex cells with slot suction. The results showed evidence of stabilization of a nearly undetached flow and attainment of an extremal lift of C y = 5.2 and a lift-to-drag ratio of K = 24 with allowance for energy losses for suction in the vortex cells.

Improvement of aerodynamic characteristics of a thick airfoil with a vortex cell in sub- and transonic flow

The modified SST model (2005) is verified using Rodi– Leschziner–Isaev's approach and the multiblock computational technologies are validated in the VP2/3 code on different-structure overlapping grids by comparing the numerical predictions with the experimental data on transonic flow around an NACA0012 airfoil at an angle of attack of 4о for М=0.7 and Re=4×106. It is proved that the aerodynamic characteristics of a thick (20% of the chord) MQ airfoil mounted at an angle of attack of 2о for Re=107 and over the Mach number range 0.3–0.55 are significantly improved because an almost circular small-size (0.12) vortex cell with a defined volumetric flow rate coefficient of 0.007 during slot suction has been located on the upper airfoil section and an intense trapped vortex has been formed in it. A detailed analysis of buffeting within the self-oscillatory regime of flow around the MQ airfoil with a vortex cell has demonstrated the periodic changes in local and integral characteristics; the lift and the aerodynamic efficiency remain quite high, but inferior to the similar characteristics at М=0.55. It is found that the vortex cell at М=0.7 is inactive, and the aerodynamic characteristics of the MQ airfoil with a vortex cell are close to those of a smooth airfoil without a cell.

Verification of the Shear-Stress Transfer Model and its Modifications in the Calculation of a Turbulent Flow Around a Semicircular Airfoil with a Zero Angle of Attack

A comparative analysis of different versions of the Menter shear-stress transfer model, including with correction for the curvature of streamlines, has been performed as applied to a periodic flow around a semicircular airfoil with a zero angle of attack at Re = 45,000. A comparison of the calculated aerodynamic coefficients Cx and Cy and the surface distribution of the pressure coefficient, averaged over the period of oscillations of the lift coefficient Cy, with the corresponding experimental data has shown that the Menter shear-stress transfer model modified within the framework of the Rody–Leshtsiner–Isaev approach with the use of the inverse function of the Richardson number correcting the eddy viscosity of a flow with a semiempirical Isaev–Kharchenko–Usachov constant equal to 0.02 is preferred compared to the other versions of this model. The errors of the calculations performed with the use of the multiblock computational technologies based on intersecting structured meshes of different scales were analyzed. The interrelation between the evolution of the structure of the periodic flow around the semicircular airfoil and the distribution of its integral force characteristics in the period of Cy oscillations is discussed.

Numerical simulation of the turbulent air flow in the narrow channel with a heated wall and a spherical dimple placed on it for vortex heat transfer enhancement depending on the dimple depth

Numerical study is made of heat transfer enhancement in the narrow channel with insulated walls in air steady flow around a heated spherical dimple, when its relative depth is varied from 0 to 0.26 (in terms of spot diameter) at a defined Reynolds number 4×104 based on bulk velocity and dimple spot diameter. The applicability of multiblock computational technologies for solution of Reynolds and energy equations with the implication of an implicit factorized finite-volume algorithm and overlapping different-scale structured grids of different topology, as well as the verification of the shear stress transfer model (SST model) modified with regard to the streamline curvature within the framework of Leschziner–Rodi–Isaev’s approach is assessed from the comparison of numerical predictions obtained by different SSTM versions. Flow regimes in a spherical dimple, as its depth is increased, are classified on the basis of the analysis of change in the jet–vortex flow structure in the dimple and its wake in the channel. In what follows, special attention is paid to asymmetric flow around a dimple with the greatest vortex heat transfer enhancement.

Optimization of the Slot Suction of Air from a Circular Vortex Cell on a Thick NACA0022 Airfoil with a Maximum Lift–Drag Ratio

On the basis of multiblock computational technologies and the Menter model of shear-stress transfer modified with account of the curvature of streamlines, the optimum position of a slot for air suction on the leeward side of the contour of a vortex cell built in a thick NACA0022 airfoil was determined for the purpose of increasing its lift–drag ratio to a maximum value in a nondisturbed air flow at a Mach number of 0.05 and an angle of attack of 7°.

Drag reduction of energy-efficient buildings and wind energy extraction due to bleeding effect

Turbulent flow around a circular cylinder with a perforated housing, when a stagnation zone flow at the forward stagnation point is transported to the near-wake region during wind energy extraction, was studied numerically using the multiblock computational technologies of solution of the Reynolds equations closed by the equations of the shear stress transfer model. It turned out that the energy extraction promoted an additional drag reduction of the energy-efficient building model under consideration.

Numerical investigation of the effect of roughness on convective heat transfer under stationary laminar flow of M20 oil around a circular cylinder

Convective heat transfer under the laminar flow (Re = 60) of M20 oil and air heated to 333 K around a circular cylinder with a wavy surface roughness is computed using multiblock computational technologies, which are implemented in code VP2/3 for solving the Navier–Stokes and energy equations as part of the procedure for adjusting pressure. It is shown that at a roughness depth of 1% in fractions of the cylinder diameter, the heat transfer from the surface in oil increases by 21%, and the thermal–hydraulic performance grows by 17%.

Analysis of extremal lift behavior of a semicircular airfoil in a turbulent airflow at a near-zero angle of attack

The experimentally discovered phenomenon of lift drop for a semicircular airfoil in a turbulent airflow at a near-zero angle of attack has been numerically analyzed with multiblock computational technologies using a shear-stress-transfer model modified with allowance for the curvature of flow lines.

Numerical Simulation of the Convective Heat Exchange in the Separation air and Oil Flows in a Staggered Bank of Round Tubes in a Wide Range of Change in the Reynolds Number

An analysis of the convective heat exchange in the separation air and oil flows in banks of heated round tubes and their hydraulic losses at Reynolds numbers changing in a wide range from 100 to 400 for the laminar flow and from 103 to 8·103 for the turbulent fl ow has been performed. For solving the Navier–Stokes and energy equations, multiblock computational technologies realized in the VP2/3 package and original procedures for correction of the pressure gradient in a fl ow and its mean-mass temperature were used. The Reynolds-averaged Navier–Stokes equations were closed using the Menter shear-stress transfer model modified with account for the curvature of streamlines within the framework of the Leshtsiner–Rody approach with an Isaev–Kharchenko–Usachov constant equal to 0.2. The results of numerical simulation were compared with the corresponding experimental data of A. Zhukaukas. The dependence of the local and integral characteristics of a fl ow of a heat-transfer agent in a staggered bank of round tubes on the properties of this agent was determined.

Simulation of the Turbulent air Flow Over a Circular Cavity with a Variable Opening Angle in an U-Shaped Channel

A numerical investigation of the influence of the opening angle of a circular cavity in an U-shaped channel and the Reynolds number of a fluid fl ow in this channel on the local characteristics and turbulence of this fl ow has been performed based on the solution of the Reynolds equations, closed by the old and new Menter shear-stress transfer models and two variants of this model accounting for the curvature of streamlines, with the use of multiblock computational technologies realized in the VP2/3 package. The results of calculations were compared with each other and with experimental data of I. Castro and R. Savelsberg. This comparison has shown that the best agreement between the numerical predictions and experiments is obtained in the case where calculations are performed within the framework of the Leshtsiner–Rody–Isaev approach with correction for the eddy viscosity of the fluid fl ow. It was established that with increase in the Reynolds number and in the opening angle of the cavity the circulation flow in the near-wall layer of the vortex trapped in the cavity intensifies at a practically constant vorticity in the core of the vortex.

Modeling a decrease in hydraulic losses during turbulent flow in a U-bend channel with a circular cavern with a large opening angle

The Reynolds equations for incompressible viscous fluid, closed using the Menter shear-stress-transfer model modified with allowance for the curvature of flow lines, have been numerically solved using multiblock computational technologies. The obtained solution has been used to calculate the turbulent flow in a U-bend channel containing a circular cavern with a variable opening angle. Predictions based on the results of numerical simulations agree well with the experimental data of Savelsberg and Castro at moderate cavern opening angles. It is established that hydraulic losses in a U-bend channel with completely open cavern are significantly (by ∼25%) decreased as compared to those in a smooth channel at Re = 105.

Visualization of a Flow in a Spherical Dimple Built in the Lower Wall of the Rectangular-Section Channel of a Water Tunnel and Numerical Identification of the Vortex-Jet Structures in It

Numerical and physical simulations of a laminar separation flow over a single spherical dimple built in the lower wall of the rectangular-section plane-parallel channel of a water tunnel were performed on the basis of the multiblock computational technologies realized in the VP2/3 package. The vortex mechanism of intensification of the heat-transfer processes in this dimple was analyzed with special emphasis on the identification of the vortex-jet structures self-generated in it.

Modeling the increase in aerodynamic efficiency for a thick (37.5% chord) airfoil with slot suction in vortex cells with allowance for the compressibility effect

The Reynolds equations closed using the Menter shear-stress-transfer model modified with allowance for the curvature of flow lines have been numerically solved using multiblock computational technologies. The obtained solution has been used to analyze subsonic flow past a thick (37.5% chord) airfoil with slot suction in circular vortex cells intended for the Ecology and Progress (Ekologiya i Progress, EKIP) aircraft project in comparison to a distributed (from the central body surface) suction at fixed values of the total volume flow rate (0.02121) and Reynolds number (105) in a range of Mach numbers from 0 to 0.4. This analysis revealed a significant (up to tenfold) decrease in the bow drag (determined with allowance for the energy losses) and a large (by an order of magnitude) increase in the aerodynamic efficiency of the thick airfoil containing vortex cells with slot suction, which reached up to 160.

Enhancement of heat transfer in unsteady laminar oil flow past a heated cylinder at Re = 150

Unsteady convective heat transfer in air and oil flows past a heated circular cylinder is modeled numerically by solving the unsteady Navier—Stokes and energy equations with the aid of multiblock computational technologies implemented in the VP2/3 code using composite overlapping structured grids of different topology. Enhancement of heat and momentum transfer is associated with a considerable reduction of temperature boundary layer thickness. Main attention is paid to a self-similar flow regime and heat transfer, with the analysis of averaged and fluctuation characteristics and the comparison of constant physical property and inhomogeneous media.

Simulation of the Wind Effect on an Ensemble of High-Rise Buildings by means of Multiblock Computational Technologies

The numerical simulation of the wind effect on an ensemble of high-rise buildings is based on the solution of Reynolds-averaged Navier–Stokes equations closed with the help of a shear stress transfer model modified with account for the influence of the curvature of streamlines with the use of multiblock computational technologies in the VP2/3 package. It has been shown that the nonstationary aerodynamics of construction ensembles of closely spaced high-rise buildings has the characteristic features inherent in tandems of blunt bodies, and the pulsating loads in the lee buildings are largely determined by the self-organization of the jet-vortex structures in the space between buildings.

Analysis of the Influence of the Temperature Factor on the Intensification of the Heat Exchange in a Lane Bank of Round Tubes in the Case of Laminar Oil Flow about It

The results of a numerical simulation of the convective heat exchange in a lane bank of round tubes in the case of laminar flow of an oil about it are presented. The Navier–Stokes and energy equations were solved using the multiblock computational technologies realized in the VP2/3 package. It is shown that, in the case of laminar M20- oil flow about a round-tube bank (of size 2 × 1), the convective heat transfer in it is ten times larger than in the case of air flow about this bank and that the velocity of the separation flow increases by two times with increase in the temperature of the tube wall from 20 to 40°C.