Numerical Investigation of Flow Past a Prolate Spheroid

2002 ◽  
Vol 124 (4) ◽  
pp. 904-910 ◽  
Author(s):  
George S. Constantinescu ◽  
Hugo Pasinato ◽  
You-Qin Wang ◽  
James R. Forsythe ◽  
Kyle D. Squires
Keyword(s):  
Skin Friction ◽  
Turbulence Model ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Prolate Spheroid ◽  
Leeward Side ◽  
Experimental Measurements ◽  
Axial Pressure ◽  
Streamline Curvature ◽  
Axial Pressure Gradient

The flowfield around a 6:1 prolate spheroid at angle of attack is predicted using solutions of the Reynolds-averaged Navier-Stokes (RANS) equations and detached-eddy simulation (DES). The calculations were performed at a Reynolds number of 4.2×106, the flow is tripped at x/L=0.2, and the angle of attack α is varied from 10 to 20 deg. RANS calculations are performed using the Spalart-Allmaras one-equation model. The influence of corrections to the Spalart-Allmaras model accounting for streamline curvature and a nonlinear constitutive relation are also considered. DES predictions are evaluated against experimental measurements, RANS results, as well as calculations performed without an explicit turbulence model. In general, flowfield predictions of the mean properties from the RANS and DES are similar. Predictions of the axial pressure distribution along the symmetry plane agree well with measured values for 10 deg angle of attack. Changes in the separation characteristics in the aft region alter the axial pressure gradient as the angle of attack increases to 20 deg. With downstream evolution, the wall-flow turning angle becomes more positive, an effect also predicted by the models though the peak-to-peak variation is less than that measured. Azimuthal skin friction variations show the same general trend as the measurements, with a weak minima identifying separation. Corrections for streamline curvature improve prediction of the pressure coefficient in the separated region on the leeward side of the spheroid. While initiated further along the spheroid compared to experimental measurements, predictions of primary and secondary separation agree reasonably well with measured values. Calculations without an explicit turbulence model predict pressure and skin-friction distributions in substantial disagreement with measurements.

Numerical Simulation and Experimental Measurement of Pressure Pulses Produced by a Pulp Screen Foil Rotor

2004 ◽  
Vol 127 (2) ◽  
pp. 347-357 ◽  
Author(s):  
Mei Feng ◽  
Jaime Gonzalez ◽  
James A. Olson ◽  
Carl Ollivier-Gooch ◽  
Robert W. Gooding
Keyword(s):  
Negative Pressure ◽  
Pressure Pulse ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Tangential Velocity ◽  
Positive Pressure ◽  
Experimental Measurements ◽  
Wide Range ◽  
Pressure Pulses ◽  
Naca 0012

Pressure screening is an efficient means of removing various contaminants that degrade the appearance and strength of paper. A critical component of a screen is the rotor, which induces a tangential velocity to the suspension and produces pressure pulses to keep the screen apertures clear. To understand the effect of key design and operating variables for a NACA foil rotor, a computational fluid dynamic (CFD) simulation was developed using FLUENT, and the results were compared to experimental measurements. Comparing the pressure pulses obtained through CFD to experimental measurements over a wide range of foil tip speeds, clearances, angles of attack, and foil cambers, general trends of the pressure pulses were similar, but the overall computed values were 40% smaller than the measured values. The pressure pulse peak was found to increase linearly with the square of tip speed for all the angles of attack studied. The maximum magnitudes of negative pressure pulse occurred for the NACA 0012 and 4312 foils at a 5deg angle of attack and for the NACA 8312 foil at 0deg. The stall angle of attack was found to be ∼5deg for NACA 8312, ∼10deg for NACA 4312, and ∼15deg for NACA 0012. The positive pressure peak near the leading edge of the foil was eliminated for foils operating at a positive angle of attack. The magnitude of the negative pressure coefficient peak increased as clearance decreased. Increased camber increases both the magnitude and width of the negative pressure pulse.

Non-Axisymmetric Turbine Endwall Aerodynamic Optimization Design: Part I — Turbine Cascade Design and Experimental Validations

2014 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Liming Song ◽  
Zhenping Feng
Keyword(s):  
Secondary Flow ◽  
Evaluation Method ◽  
Pressure Coefficient ◽  
Optimization Method ◽  
Experimental Measurements ◽  
Turbine Cascade ◽  
Aerodynamic Optimization ◽  
Flow Losses ◽  
Flow Intensity ◽  
Performance Evaluation Method

The non-axisymmetric endwall profiling has been proven to be an effective tool to reduce the secondary flow loss in turbomachinery. In this work, the aerodynamic optimization for the non-axisymmetric endwall profile of the turbine cascade and stage was presented and the design results were validated by annular cascade experimental measurements and numerical simulations. The parametric method of the non-axisymmetric endwall profile was proposed based on the relation between the pressure field variation and the secondary flow intensity. The optimization system combines with the non-axisymmetric endwall parameterization method, global optimization method of the adaptive range differential evolution algorithm and the aerodynamic performance evaluation method using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k–ω SST turbulent with transition model solutions. In the part I, the optimization method is used to design the optimum non-axisymmetric endwall profile of the typical high loaded turbine stator. The design objective was selected for the maximum total pressure coefficient with constrains on the mass flow rate and outlet flow angle. Only five design variables are needed for one endwall to search the optimum non-axisymmetric endwall profile. The optimized non-axisymmetric endwall profile of turbine cascade demonstrated an improvement of total pressure coefficient of 0.21% absolutely, comparing with the referenced axisymmetric endwall design case. The reliability of the numerical calculation used in the aerodynamic performance evaluation method and the optimization result were validated by the annular vane experimental measurements. The static pressure distribution at midspan was measured while the cascade flow field was measured with the five-hole probe for both the referenced axisymmetric and optimized non-axisymmetric endwall profile cascades. Both the experimental measurements and numerical simulations demonstrated that both the secondary flow losses and the profile loss of the optimized non-axisymmetric endwall profile cascade were significantly reduced by comparison of the referenced axisymmetric case. The weakening of the secondary flow of the optimized non-axisymmetric endwall profile design was also proven by the secondary flow vector results in the experiment. The detailed flow mechanism of the secondary flow losses reduction in the non-axisymmetric endwall profile cascade was analyzed by investigating the relation between the change of the pressure gradient and the variation of the secondary flow intensity.

A Numerical Procedure for Modelling the Thermal Performance of Ventilated Hollow Core Slabs

2016 ◽  
Vol 846 ◽  
pp. 12-17
Author(s):  
Ahmed Faheem ◽  
Gianluca Ranzi ◽  
Francesco Fiorito ◽  
Cheng Wang Lei
Keyword(s):  
Turbulence Model ◽  
Thermal Performance ◽  
Numerical Procedure ◽  
Turbulence Models ◽  
Experimental Measurements ◽  
Hollow Core ◽  
Horizontal Pipe ◽  
Dimensionless Velocity ◽  
Nusselt Numbers ◽  
Numerical Predictions

This paper presents a numerical procedure for modelling the thermal performance of ventilated hollow core slabs (VHCS). A turbulence model suitable for this purpose is identified first by considering a smooth horizontal pipe subjected to turbulent mixed convention conditions typical of VHCSs. Comparison of the fully-developed dimensionless velocity (u+) and temperature (T+) profiles as well as the Nusselt numbers (Nu) predicted by five different turbulence models against empirical expressions available in the literature shows that the Standard and Realisable k-ε models provide the best overall predictions of u+, T+ and Nu. Since the Standard k-ε model gives slightly better estimates of the Nu values, it is adopted to model the thermal performance of a VHCS geometry for which experimental thermal responses are reported in the literature. The numerical predictions of local temperatures within the VHCS agree well with the experimental measurements, and hence the Standard k-ε model is recommended here for the modeling of VHCSs.

scholarly journals Study of board bending degree on hydrodynamic performances of a single-layer cambered otter-board

2019 ◽  
Vol 131 ◽  
pp. 01120
Author(s):  
Lei Wang ◽  
Lu Min Wang ◽  
Yong Li Liu ◽  
Wen Wen Yu ◽  
Guang Rui Qi ◽  
...  
Keyword(s):  
Center Of Pressure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Single Layer ◽  
Moment Coefficient ◽  
Pitch Moment ◽  
Engineering Models ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The effect of board bending degree on hydrodynamic performances of a single-layer cambered otter-board was investigated using engineering models in a wind tunnel. Three different bending degree boards were evaluated at a wind speed of 28 m/s. Parameters measured included: drag coefficient Cx, lift coefficient Cy, pitch moment coefficient Cm, center of pressure coefficient Cp , over a range of angle of attack (0° to 70°). These coefficients were used in analyzing the differences in the performance among the three otter-board models. Results showed that the bending of the board(No. 2, No. 3) increased the water resistance of the otter-board, and improved the lift coefficient of the otter-board in the small angle of attack (0°<α≤20 °) ; the maximum lift coefficients Cy of otter-board model (No. 1) was higher (1.680, α = 25°). the maximum lift–drag ratios of models (No. 1, No. 2 and No. 3) are 6.822 (α = 7.5 °), 6.533 (α = 2.5 °) and 6.384 (α = 5.0°), which showed that the board bending reduces the lift-to-drag ratio of the otter-board.The stability of the No. 3 model was better than those two models (No. 1, No. 2) in most range of attack angle, but No. 1 otter-board model had a better stability in roll of otter-board. The findings of this study can offer useful reference data for the structural optimization of otter-boards for trawling.

scholarly journals Evaluation of CFD Predictions Using Thermal Field Measurements on a Simulated Film Cooled Turbine Blade Leading Edge

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Sibi Mathew ◽  
Silvia Ravelli ◽  
David G. Bogard
Keyword(s):  
Turbine Blade ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Stagnation Line ◽  
Thermal Fields ◽  
Sst Model ◽  
Adiabatic Effectiveness ◽  
Blade Leading Edge

Computational fluid dynamics (CFD) predictions of film cooling performance for gas turbine airfoils are an important part of the design process for turbine cooling. Typically, industry relies on the approach based on Reynolds Averaged Navier Stokes equations, together with a two-equation turbulence model. The realizable k-ɛ (RKE) model and the shear stress transport k-ω (SST) model are recognized as the most reliable. Their accuracy is generally assessed by comparing to experimentally measured adiabatic effectiveness. In this study, the performances of the RKE and SST models were evaluated by comparing predicted and measured thermal fields in a turbine blade leading edge with three rows of cooling holes, positioned along the stagnation line and at ±25 deg. Predictions and measurements were done with high thermal conductivity models which simulated the conjugate heat transfer effects between the coolant flow and the solid. Particular attention was placed on the thermal fields along the stagnation line, and immediately downstream of the off-stagnation line row of holes. Conventional evaluations in terms of adiabatic effectiveness were also carried out. Predictions of coolant flows at the stagnation line were significantly different when using the two different turbulence models. For a blowing ratio of M = 2.0, the predictions with the SST model showed coolant jet separation at the stagnation line, while the RKE predictions showed no separation. Experimental measurements showed that there was coolant jet separation at the stagnation line, but the actual thermal fields obtained from experimental measurements were significantly different from that predicted by either turbulence model. Similar results were seen for predicted and measured thermal fields downstream of the off-stagnation row of holes.

Boundary layer over a blunt body at low incidence with circumferential reversed flow

1975 ◽  
Vol 72 (1) ◽  
pp. 49-65 ◽  
Author(s):  
K. C. Wang
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Blunt Body ◽  
Three Dimensional ◽  
Prolate Spheroid ◽  
Three Dimensions ◽  
General Context ◽  
Reversed Flow ◽  
Low Incidence

This paper investigates the three-dimensional laminar boundary layer over a blunt body (a prolate spheroid) at low incidence and with reversed flow. Results reflecting the general characteristics of such a problem are presented. More significant are the features relating to the circumferential flow reversal. Some of these features confirm our early hypotheses concerning the existence of a reversed region ahead of separation and the role of the zero-cfθ line in the general context of separation in three dimensions. Other features are unexpected, including the distribution of cfμ and the shape of the separation line. Here cfθ and cfμ denote, respectively, the circumferential and meridional components of the skin friction.

scholarly journals Heat Transfer in Air Flow Past a Bottom Channel Wall-Attached Diamond-Shaped Baffle – Using a CFD Technique

2019 ◽  
Vol 63 (2) ◽  
pp. 100-112 ◽  
Author(s):  
Younes Menni ◽  
Ali J. Chamkha ◽  
Chafika Zidani ◽  
Boumédiène Benyoucef
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Dynamic Pressure ◽  
Turbulent Viscosity ◽  
Pressure Coefficient ◽  
Operating Conditions ◽  
Computational Domain ◽  
Thermal Transfer ◽  
Transfer Characteristics ◽  
Convective Thermal

A computational analysis has been conducted to investigate turbulent flow and convective thermal transfer characteristics in a two-dimensional horizontal rectangular section channel with a hot lower wall-mounted diamond-shaped baffle. The calculations are based on the finite volume method, by means of Commercial Computational Fluid Dynamics software FLUENT, standard k-epsilon turbulence model with QUICK numerical scheme, and the SIMPLE discretization algorithm has been applied. The fluid flow and heat transfer characteristics, i.e., dynamic pressure coefficient, stream function, mean, axial, and transverse velocities, turbulent viscosity, temperature field, skin friction coefficients, local and average Nusselt numbers, and thermal enhancement factor are presented for flow Reynolds numbers based on the aeraulic diameter of the computational domain ranging from 12,000 to 32,000 at constant surface temperature condition along the upper and lower walls. Effect of the diamond configuration of the insulated baffle is studied numerically and the data obtained from this same baffle model are also compared with that of the simple flat rectangular baffle under similar operating conditions. Over the range under investigation, the improvements are found to be around 3.962 and 29.820 times higher than the smooth air channel with no baffle for heat thermal transfer and skin friction factor, respectively. The maximum TEF is around 1.292 at the highest Reynolds number value, Re = 32,000.

Correction to the Spalart–Allmaras Turbulence Model, Providing More Accurate Skin Friction

AIAA Journal ◽  
2020 ◽  
Vol 58 (5) ◽  
pp. 1903-1905 ◽  
Author(s):  
Philippe R. Spalart ◽  
Andrey V. Garbaruk
Keyword(s):  
Skin Friction ◽  
Turbulence Model
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