Drag Values Research Articles

Fatigue Failure Analysis of Bottom Hole Assembly during the Drilling of H-E1 and H-Q1 Wells in the Hululais Geothermal Field

In drilling operations it is intended to be able to conduct drilling quickly without causing damage to the drilling equipment and be able to produce good quality wells. Failure on the drilling pipe or bottom hole assembly (BHA) ranks results from loading that exceeds the maximum strength limit of the material. In this study, the calculation of the load on the downhole motor, where in the depth of the drill 512 meters failure occurs in the form of broken downhole motor. Based on the analysis conducted, at a depth of 494 meters the value of the hookload has increased quite high at 131.8 klb, while the maximum allowable hookload value is 121 klb, this indicates an overpull of 10.8 klb and based on the calculation of the drag value, a drag is obtained 38.8 klb while the maximum drag value is 28 klb, the difference between the actual drag value and the maximum allowable drag value is 10.8 klb, so it can be concluded that the failure that occurs in BHA # 10 is due to a drag that exceeds the maximum limit of 10.8 klb.

A Comparative Study of Aerodynamic Coefficients on Tall Structures using Experimental Studies with International Codes and Standards

This paper illustrates the comparison of aerodynamic forces and coefficients on rectangular tall buildings. The forces and coefficients were obtained using Wind Tunnel Experiment and various international code provisions and standards. Rectangular tall building models selected for the study were made of acrylic sheets with various geometric scales. The models were tested using low-speed wind tunnel for various angles of incidents of wind varying from 0° to 90°. Drag coefficients obtained from experiments were compared with values of mean drag coefficients obtained from codes and practices, (a) IS: 875(Part3): Wind Loads on Buildings and Structures (India, 2015), (b) AS/NZS1170.2:2011, the combined Australia/New Zealand Standard on Wind Actions (Standards Australia,2011); (c) ASCE7–10 (ASCE, 2010); and (d) HKCoP-2019, the Code of Practice on Wind Effects in Hong Kong, (Buildings Department HongKong, 2019). Buildings with the same plan aspect ratio show the same aerodynamic behaviour. Wind tunnel study over-predicts the coefficient values compared to standards and practices. The average coefficient of drag values from codes is in good agreement with wind tunnel data with a deviation of less than 15%. The study also includes an examination of parameters such as pitching moment and its coefficient.

Experimental and Numerical Investigation of Stepped Planing Hulls in Finding an Optimized Step Location and Analysis of Its Porpoising Phenomenon

Stability of a high-speed craft is an essential matter, and porpoising is one of the most critical instabilities that could occur in some planing hulls due to inappropriate design. In this paper, the porpoising phenomenon and variation of step location yielding resistance reduction are studied through experimental and numerical methods. The investigated models include a single-step model and a nonstep model with the same general shape, but with different step location. The nonstep model is previously tested, but the single-step model is examined in the present study. The nonstep model experiences porpoising at 8 m/s speed, but the single-step model remains stable at the same speed. A three-dimensional CFD analysis is conducted using the finite volume method (FVM). On the contrary, the volume of fluid (VOF) scheme is used for free surface modeling, and the overset mesh technique is implemented within StarCCM+ software. The CFD results of total hydrodynamic resistance and dynamic trim angle are compared against the experimental data. The numerical results are in good agreement with the experimental data. Subsequently, ten different stepped models are simulated to examine their effects. The longitudinal distance between steps and aft of these models are in the range of 19 to 50 percent of the length of models. The obtained results show that as steps are located farther than aft, the models become more stable, and resistance increases due to trim reduction. Finally, the optimum location of the step is extracted with the aim of minimizing the resistance through the design of experiment (DOE) method. Based on the DOE method, it is observed that the sensitivity of the drag value to the step location is higher than the speed.

How to extract the angle attack on airfoils in cycloidal motion from a flow field solved with computational fluid dynamics? Development and verification of a robust computational procedure

One of the key problems faced by researchers dealing with Computational Fluid Dynamics simulations and rotating machines is represented by how to extract the angle attack from a numerically computed flow field. If this issue has been addressed successfully for some applications, in case of airfoils moving in cycloidal motion (i.e. having a rotational motion within a rectilinear flow field, like in Darrieus Vertical-Axis Wind Turbines) some proposals do exist, but always affected by some arbitrary choices on the velocity probing that are not supported by a proper verification. The aim of the present study is to try finding a robust computational procedure tailored for the scope. To this end, three different post-processing methods - detailed in the study – were considered and applied to the flow fields of 2-blade H-Darrieus rotor, coming from a high-fidelity unsteady model based on Computational Fluid Dynamics; the resulting blade angle of attack trends over one rotor revolution were then combined with available blade forces data to assess the corresponding lift and drag coefficients. In order to assess the actual accuracy of these approaches for a stable tip-speed ratio, the post-processed force coefficients were compared to the ones computed via a numerical pitching airfoil model, which received the sampled angle of attack trends as input; eventually, the pitched lift and drag values have been used to reconstruct the blade forces over one rotor revolution and compare them with the ones coming from full turbine simulations. Results show large scattering of obtained data, remarking the importance of the proper selection of the angle of attack sampling strategy for the analysis of turbine performance. Overall, the “LineAverage” approach, i.e. the use of multiple sampling points around the airfoil for velocity probing, has proved to be the most accurate method.

Investigating the effects of leading-edge tubercles on the aerodynamic performance of insect-like flapping wing

Tubercles are small protuberances or bumps on the leading edge of humpback whale's pectoral fin. To examine the effects of leading-edge tubercles on the aerodynamic performance of a flapping wing, lift, drag, and power coefficients are obtained from numerical simulations. A revolving wing (one-degree-of-freedom azimuth rotation; rotation in a horizontal plane after an initial acceleration) with leading-edge tubercles at an angle of attack of 40° and Reynolds number of 400 is used in the present study. The reason for choosing azimuth rotation is that it resembles downstroke and upstroke of flapping motion of an insect. A rigid rectangular wing with six different combinations of wavelengths ( λ = 10% and 50% of the chord length) and amplitudes ( A = 2.5%, 5%, and 10% of the chord length) are chosen for this study. These parameters are inspired by the tubercles present at the leading edge of humpback whales' pectoral fin. It was observed that generally, tubercles degraded the aerodynamic performance of the wings in terms of lift, drag, and power coefficients. Although some of the tubercle leading-edge wings showed lower drag (2.20% lower) and lower power coefficient (2.12% lower) values than the baseline wing, none of the tubercle wing performed better than the baseline wing in terms of aerodynamic performance parameters; aerodynamic efficiency ([Formula: see text]) and power economy ([Formula: see text]). Hence, it was concluded that the tubercles are not advantageous over the straight leading-edge wing for azimuth rotating hovering insect-like motion and further investigation is required to explore its potential benefits.

Aerodynamics of curved underbody diffusers using CFD

This paper presents new results concerning aerodynamics of a bluff body fitted with non-flat underbody diffusers. For the current study a computational approach is used, taking the advantage that CFD has become a valuable and important tool in road vehicle aerodynamics. There are analyzed two basic shapes, namely circular and the elliptical surfaces. As in previous investigations performed, angle and length of the diffuser are the parameters systematically varied within ranges relevant for a hatchback passenger car. Coefficients of lift and drag are computed and compared with the values obtained for the flat underbody diffuser. In order to get a better overview, 3D maps of both lift and drag coefficients were generated using polynomial interpolation of their values. The results reveal significant improvements concerning the lift generated by body fitted with curved diffusers, which are emphasised by an average growth of the downforce larger than 20%. In addition, for small and moderate angles, and small diffuser lengths, the curved diffusers lead also to smaller values of drag, compared to the plane diffusers. Thus, short diffusers with curved sections work better from aerodynamic point of view. In terms of vehicles design, short diffusers have also the advantage of small interferences with other underbody components of cars, as rear wheelhouses and rear silencer. In addition, they offer a significant larger cargo space.

The flow past a flatback airfoil with flow control devices: benchmarking numerical simulations against wind tunnel data

Abstract. As wind turbines grow larger, the use of flatback airfoils has become standard practice for the root region of the blades. Flatback profiles provide higher lift and reduced sensitivity to soiling at significantly higher drag values. A number of flow control devices have been proposed to improve the performance of flatback profiles. In the present study, the flow past a flatback airfoil at a chord Reynolds number of 1.5×106 with and without trailing edge flow control devices is considered. Two different numerical approaches are applied, unsteady Reynolds-Averaged Navier Stokes (RANS) simulations and detached eddy simulations (DES). The computational predictions are compared against wind tunnel measurements to assess the suitability of each method. The effect of each flow control device on the flow is examined based on the DES results on the finer mesh. Results agree well with the experimental findings and show that a newly proposed flap device outperforms traditional solutions for flatback airfoils. In terms of numerical modelling, the more expensive DES approach is more suitable if the wake frequencies are of interest, but the simplest 2D RANS simulations can provide acceptable load predictions.

Low-frequency unsteadiness in the flow around a square cylinder with critical angle of [formula omitted] at the Reynolds number of [formula omitted

Numerical simulations with high grid resolutions are conducted to investigate the flow past a square cylinder at the Reynolds number of 2.2×104 and the critical angle of attack of 14°. The focus is on the unsteadiness with a much lower frequency than that of von Karman vortex shedding. This study confirms the existence of low-frequency unsteadiness even for the square cylinder. The qualitative and quantitative features of low-frequency unsteadiness are systematically analyzed in terms of forces, vortex shedding and separation bubble. The low frequency with the outstanding peak is much lower than the frequency of von Karman vortex shedding; specifically, it is about 0.14fvK, where fvK is the vortex-shedding frequency. The low-frequency unsteadiness can be “felt” in the time series of forces and in the dynamics of vortex shedding and separation bubble. For both drag and lift, the unsteadiness is manifested by the low-frequency modulation of force amplitude and by the low-frequency periodic variation between the high and low values of the mean drag and lift over a vortex shedding cycle. The smaller force amplitude is accompanied simultaneously by the vortex shedding with longer formation length and weaker spanwise correlation, together with longer separation bubble on the flow-reattachment side of the cylinder.

Taper stacking for the aerodynamic performance of wings

PurposeThe critical Mach number, lift-to-drag ratio and drag force play important role in the performance of the wings. This paper aims to investigate the effect of taper stacking, which has been used to generalize wing sweeping, on those parameters.Design/methodology/approachThe results obtained are based on steady-state turbulent flowfields computations. The baseline wing is ONERA M6. Various wing planforms are generated by linearly or parabolically varying the spanwise stacking location. The critical Mach number is determined by changing the freestream Mach number for a fixed angle of attack. On the other hand, the analysis of the drag force is carried out by changing the angle of attack to keep the lift force constant.FindingsBy changing the stacking location, the critical Mach number and the corresponding lift-to-drag ratio have increased by around 7 and 3%, respectively. A reduction of 12.8% in total drag force has been observed in one of the analyzed cases. Moreover, there exist some cases in which the values of drag reduce significantly while the lift is the same.Practical implicationsThe results of this new stacking approach have implied that the drag force can be decreased without decreasing the lift. This outcome is valuable for increasing the range and endurance of an aircraft.Originality/valueThis work generalizes wing sweeping by modifying the taper stacking along the span. In literature, wing sweep is enhanced using segmented stacking of taper distribution. The present study is further enhancing this concept by introducing continuous stacking (infinite number of stacking segments) for the first time.

Investigation on Effecting Parameters of the Wind Disturbance on Stability of the Steering System

In self-driving vehicles, it is necessary to control the steering system fully. In this paper, the pressure and the velocity distributions on the surface of the vehicle’s body under the influence of wind have been studied at different angles (35°, 90°, and 125°). The parameters that affect the steering system of the self-driving vehicle have been studied, affected by another vehicle (SUV) using the CFX ANSYS (18.2) and the SOLIDWORKS simulation programs. The torque and the effort have been calculated on the steering system by using the mathematical equation in the MATLAB program. The results have showed the highest torque and the effort values when the wind has faced the car at an angle of 125 degrees and the highest drag value when the vehicle has been in front of the SUV. The maximum pressure distribution is recorded when the air is 90 degrees. The highest effort is on the steering wheel when the SUV is next to the vehicle.

Characterization and CFD Analysis of Traditional Vessels of Kerala

In this study, analysis of the hull forms of traditional vessels in Kerala, viz., Snake boat, Uru and Houseboat have been studied. Ideal draft from wave cut analysis, estimation of drag forces, pressure and velocity contours on the surface of the hulls has been studied using a proposed 3-D model. The CFD package SHIPFLOW 5.1® has been used for the hydrodynamic analysis of ship/vessel in this work. The wave-elevation vectors (Kelvin wave pattern) at different Froude numbers and the different draft has been evaluated along the length of the vessel. The results show that that out of the total drag force experienced by a Snake boat at the ideal draft, 66.8% is attributed to the frictional drag and only 33.2% is wave-making resistance drag. These values change to 73.1% and 26.9% respectively for Uru and 23.7% and 76.3% for a Houseboat. With regards to the magnitude of resistance drag values, the total resistance experience by an Uru when compared to Snake boat and Houseboat are 30.16 and 1.17 times respectively. It has also been found that the presence of the skeg improves the hydrodynamic performance of the Houseboat considerably. The findings will be useful to design these boats considering its specific applications.

Estimation of an Elite Road Cyclist Performance in Different Positions Based on Numerical Simulations and Analytical Procedures.

The aim of this study was to use numerical simulations and analytical procedures to compare a cyclist's performance in three different cycling positions. An elite level road cyclist competing at a national level was recruited for this research. The bicycle was 7 kg and the cyclist 55 kg. A 3D scan was taken of the subject on the competition bicycle, wearing race gear and helmet in the upright position, in the handlebar drops (dropped position) and leaning on the elbows (elbows position). Numerical simulations by computer fluid dynamics in Fluent CFD code assessed the coefficient of drag at 11.11 m/s. Following that, a set of assumptions were employed to assess cycling performance from 1 to 22 m/s. Drag values ranged between 0.16 and 99.51 N across the different speeds and positions. The cyclist mechanical power in the elbows position differed from the upright position between 0 and 23% and from the dropped position from 0 to 21%. The cyclist's energy cost in the upright position differed 2 to 16% in comparison to the elbows position and the elbows position had less 2 to 14% energy cost in comparison to the dropped position. The estimated time of arrival was computed for a 220,000 m distance and it varied between 7,715.03 s (2 h:8 min:24 s) and 220,000 s (61 h:6 min:40 s) across the different speeds and positions. In the elbows position, is expected that a cyclist may improve the winning time up to 23% in comparison to he upright and dropped position across the studied speeds.

An IDDES investigation of Jacobs bogie effects on the slipstream and wake flow of a high-speed train

This study numerically investigates the effects of Jacobs bogies on the aerodynamic behaviors of a high-speed train using improved delayed detached eddy simulation (IDDES) at Re ​= ​3.3 ​× ​105. The results of the numerical simulations have been validated against the experimental data obtained from a previous reduced-scale moving model test and a wind tunnel test. The slipstream velocity, wake flow, underbody flow and aerodynamic drag of the HST are compared between the conventional bogie case and Jacobs bogie case. The results show that the use of Jacobs bogies can reduce the TSI values of the slipstream velocity at trackside and platform positions by 11.07% and 22.40%, respectively, which thereby shows a positive effect on improving the safety level of trackside workers and passengers standing on the platform. The Jacobs bogies are found to decrease the maximum values of the slipstream velocity and turbulence kinetic energy occurring at the intermediate bogie regions beneath the HST by 30.08% and 41.32%, respectively, which is beneficial for weakening the ballast flight phenomenon. The Jacobs bogies significantly narrow the scale of the longitudinal vortex structure in the wake propagation region. Additionally, the application of Jacobs bogies lowers the aerodynamic drag values of the vehicles and contributes to a 10% total drag reduction.

The Aerodynamics and Energy Cost Assessment of an Able-Bodied Cyclist and Amputated Models by Computer Fluid Dynamics.

Background and Objectives: The aim of this study was to assess and compare the drag and energy cost of three cyclists assessed by computational fluid dynamics (CFD) and analytical procedures. Materials and methods: A transradial (Tr) and transtibial (Tt) were compared to a full-body cyclist at different speeds. An elite male cyclist with 65 kg of mass and 1.72 m of height volunteered for this research with his competition cloths, helmet and bicycle with 5 kg of mass. A 3D model of the bicycle and cyclist in the upright position was obtained for numerical simulations. Upon that, two more models were created, simulating elbow and knee-disarticulated athletes. Numerical simulations by computational fluid dynamics and analytical procedures were computed to assess drag and energy cost, respectively. Results: One-Way ANOVA presented no significant differences between cyclists for drag (F = 0.041; p = 0.960; η2 = 0.002) and energy cost (F = 0.42; p = 0.908; η2 = 0.002). Linear regression presented a very high adjustment for absolute drag values between able-bodied and Tr (R2 = 1.000; Ra2 = 1.000; SEE = 0.200) and Tt (R2 = 1.00; Ra2 = 1.000; SEE = 0.160). The linear regression for energy cost presented a very high adjustment for absolute values between able-bodied and Tr (R2 = 1.000; Ra2 = 1.000; SEE = 0.570) and Tt (R2 = 1.00; Ra2 = 1.00; SEE = 0.778). Conclusions: This study suggests that drag and energy cost was lower in the able-bodied, followed by the Tr and Tt cyclists.

Analysis of Cyclist's Drag on the Aero Position Using Numerical Simulations and Analytical Procedures: A Case Study.

Background: Resistance acting on a cyclist is a major concern among the cycling fraternity. Most of the testing methods require previous training or expensive equipment and time-consuming set-ups. By contrast, analytical procedures are more affordable and numerical simulations are perfect for manipulating and controlling inputs. The aim of this case study was to compare the drag of a cyclist in the aero position as measured using numerical simulation and analytical procedures. Methods: An elite male cyclist (65 kg in mass and 1.72 m in height) volunteered to take part in this research. The cyclist was wearing his competition gear, helmet and bicycle. A three-dimensional model of the bicycle and cyclist in the aero position was obtained to run the numerical simulations. Computational fluid dynamics (CFD) and a set of analytical procedures were carried out to assess drag, frontal area and drag coefficient, between 1 m/s and 22 m/s, with increments of 1 m/s. The t-test paired samples and linear regression were selected to compare, correlate and assess the methods agreement. Results: No significant differences (t = 2.826; p = 0.275) between CFD and analytical procedures were found. The linear regression showed a very high adjustment for drag (R2 = 0.995; p < 0.001). However, the drag values obtained by the analytical procedures seemed to be overestimated, even though without effect (d = 0.11). Conclusions: These findings suggest that drag might be assessed using both a set of analytical procedures and CFD.

An Aerodynamic Assessment of Vehicle-Side Wall Interaction using Numerical Simulations

The effects of induced pressure loads from a realistic vehicle onto the surface of a road-side wall are numerically investigated. Parameters such as vehicle speeds, vehicle-wall separation distances and the effects of inclined walls are examined to numerically characterize the vehicle-wall interactions. Aerodynamic characteristics such as the drag, lift, side forces and pressure coefficients are analyzed on the vehicle to provide a basis for comparison between each of the aforementioned variations. Our results demonstrate that a smaller separation distance between vehicle and wall enhances the pressure induced on both the wall and car which is found to be consistent with the experimental data published previously. We find that the presence of a wall in close proximity to the passing vehicle unfavourably influences the induced pressure on the side-wall and abruptly increases the drag, lift and side forces experienced by the vehicle. For a vertical side-wall, from a wall separation point of view, a separation distance of 1.35 normalized by the height of the vehicle tends to retrieve the cars’ original drag and lift value. In addition, our results demonstrate that a wall inclined to the ground favourably influences the aerodynamic characteristics of the vehicle compared to its vertical counterpart.

Numerical Simulation of Drag Reduction on a Square Rod Detached with Two Control Rods at Various Gap Spacing via Lattice Boltzmann Method

Numerical simulations are performed to examine the effect of size of control rods (d1) and spacing ratio (g) on flow around a square rod with upstream and downstream control rods aligned in-line using the lattice Boltzmann method (LBM). The Reynolds number (Re) is fixed at Re = 160, while the spacing between the main rod and control rods is taken in the range 1 ≤ g ≤ 5 and the size of the control rod is varied between 4 and 20. Seven different types of flow mods are observed in this study at different values of g and d1. Variation in force statistics, like mean drag coefficient (Cdmean), Strouhal number (St), root mean square values of drag (Cdrms) and lift coefficients (Clrms), and percentage reduction in mean drag coefficient is discussed in detail. It was examined that vortex shedding completely suppressed at (g, d1) = (1, 12), (2, 12), and (2, 16) where steady flow mode exists. Moreover, it was found that at large gap spacing, where g = 5, the effect of control rods on the main rod vanishes. Due to this strong vortex shedding produced and as a result, maximum value of Cdmean is found at (g, d1) = (5, 8). The negative values of mean drag force are also observed at some gap spacing and size of control rods are due to the effect of thrust. Furthermore, the maximum percentage reduction in Cdmean is 121%, found at (g, d1) = (2, 20).

Drag-based aerodynamic braking system for the Hyperloop: a numerical study

The Hyperloop promises to revolutionize the transport infrastructure of the 21st century by reducing travel time and allowing people to reach transonic speed on land. It carries with it the hope of a sustainable transportation system during an era of global energy crisis. Overall passenger safety in a high-speed pod necessitates a reliable braking system. This paper introduces the possibility of utilizing aerodynamic drag in the Hyperloop, anticipated to operate at high Mach and low Reynolds flow regime, to attenuate the speed of the pod. Numerical analysis was conducted to investigate the effect of incorporating an aerodynamic brake at different pod velocities (100, 135, and 150 m/s) and deployment angles (30°, 45°, 60°, and 90°). A detailed comparison between the proposed aerodynamic braking system (AeBS) and existing braking systems for the Hyperloop has been presented in this paper. The results demonstrate an increase in drag value of the pod by 3.4 times using a single 0.15 m2brake plate. When the brake plate was fully deployed at a pod velocity in excess of 112 m/s, the aerodynamic drag-based braking systems was shown to be more effective than the contemporary eddy current braking system.

Numerical Analysis of Fluid Forces for Flow Past a Square Rod with Detached Dual Control Rods at Various Gap Spacing

A two-dimensional numerical study was conducted for flow past a square rod in the presence of two control rods. One is placed vertically in the upstream direction and the second one is placed horizontally in the downstream direction of the square rod. The influence of gap spacing was studied by taking g1 = 1–5 and g2 = 0.5–5 (where g1 is the gap between the upstream control rod and the main rod, and g2 is the space between the main rod and the downstream control rod) at Re = 160. The simulation results were obtained in the form of vorticity contour, drag and lift coefficients, Strouhal number, and force statistics. Under the effect of gap spacing, three different flow modes were found and named according to their behavior. It was found that the mean drag coefficient showed decreasing behavior by increasing the value of g2 continually at a fixed value of g1. The largest value of C d m e a n was found at (g1, g2) = (1, 1) and the greatest percentage reduction in C d m e a n was obtained at (g1, g2) = (1, 3), which is 139.72%. The effect of thrust was also noticed for all selected values of g1 and g2. Furthermore, it was noticed that the Strouhal number and the root mean square values of the drag and lift coefficients smaller values than the single rod values, except for the Clrms value of (g1, g2) = (1, 3) and (1, 4).

Aerogami: Composite origami structures as active aerodynamic Ccontrol

This study explores the use of origami composite structures as active aerodynamic control surfaces. Towards this goal, two origami concepts were designed leveraging a combination of analytical and finite element modeling, and computational fluid dynamics simulations. Wind tunnel tests were performed at different dynamic pressures in conjunction with two different active control laws to test the capability of obtaining desired drag values. The experiments revealed excellent structural rigidity and folding characteristics under aerodynamic loading. These results are in very good agreement with one-way Fluid Structure Interaction (FSI) simulations, which show the potential of using high-fidelity modeling for the design and optimization of these structures.Future work will focus on developing advanced origami designs that allow for more deterministic folding as well as improved weight, stiffness, and fatigue characteristics in the use of materials.