Oncoming Velocity Research Articles

Flapping dynamics of a flexible membrane attached to the leading edge of a forward-facing step

An experimental investigation of velocity fields over and wall pressure fluctuations on a forward-facing step (FFS) disturbed by a flexible membrane has been conducted. A two-dimensional flexible membrane of 40mm length and 0.15mm thickness attached to a FFS of 40mm height was tested with oncoming velocity in the range of 7.3 < U < 12.9 m/s, corresponding to Reynolds numbers of 20391 < ReH < 35312 based on the step height. A high-speed camera was used to reconstruct the configuration of the flapping membrane. The flow field velocity dataset in the horizontal-vertical plane and the pressure fluctuation on the step surface were measured by planar particle image velocimetry and pressure sensors, respectively. The flexible membrane displayed two distinct modes, viz. a bending mode or flapping mode. In the bending mode, the membrane elevates the shear layer, thereby delaying the reattachment of separation flow generated by a FFS. In the flapping mode, the membrane periodically generates flapping-induced vortices (FIVs) of different scales with varying Reynolds numbers. The pressure on the FFS also undergoes periodic fluctuations corresponding to these FIVs.

Energy Harnessing Performance of Oscillating Foil Submerged in the Wake of a Fixed Cylinder

The energy harnessing from flow-induced vibrations (FIV) by an oscillating foil placed tandemly behind a circular cylinder (which serves as a vortex generator) is investigated. The foil is submerged in the wake produced by the fixed cylinder and could oscillate in the direction perpendicular to the incoming flow with single-degree freedom. The spacing ratio ranges from 1.0 to 5.0. The oncoming fluid velocity is U = 1–10 m/s, corresponding to the reduced velocity Ur = 3.81–38.08 and the Reynolds number Re = 9.58 × 103–9.58 × 104. Four harnessing damping ratios (ζharness = 0.0054–0.0216) are used to simulate the energy conversion conditions. The main conclusions are: (1) The optimal oscillation pattern related to the highest harnessed energy emerges as the spacing ratio close to 1.0. (2) The airflow energy converted by the foil is positively correlated with the harnessing damping ratio because the amplitude responses are similar at various harnessing damping ratios. A high velocity yields the highest harnessed power. (3) The harnessing efficiency of the foil could reach 48.89%, which is much more than that of an isolated flapping foil.

Effect of area ratio and heat release method on the Ma∞ = 2-6 operation performance of rocket-based combined cycle engine

Ballistic trajectories with rapidly changing and variable ambient conditions impose higher requirements on integral multi-component rocket-based combined cycle (RBCC) engines. A central strut-based RBCC engine was numerically simulated by solving Reynolds-averaged Navier-Stokes equations together with a k-ω SST turbulence model under various flight conditions, Ma∞=2 to Ma∞=6, which cover ejector, ramjet and scramjet modes. Ground direct-connect tests were carried out to analyze heat release performance in the combustor and the pressure balance relationship between various components. Results indicate that scramjet combustion should be conducted in the foremost combustor where geometry expansion is slightest. As the oncoming velocity decreases, the combustor expansion ratio should be increased and the location of heat addition moves to downstream larger area region. Distributed fuel injection with 20%∼30% upstream is beneficial for increasing the initial temperature of the mixing gas and thus the combustion efficiency under Ma∞3-6 conditions. At lower flight Mach numbers (Ma∞<3), different dual-ramjet engine, a section with larger area ratio, over 2, should be added behind the ramjet combustor. Since off-design inlet operation causes a decrease on the intake mass flow rate, concentrated heat addition should be adopt to ensure effective thermal choking.

Lock-in prediction for vortex-induced vibrations of a long hanged and weighted riser in internal fluid flow and external currents

The occurrence of lock-in, a local synchronization between the vortex shedding and cross-flow (CF) structural vibration frequencies, is investigated for a long flexible riser, of which the top is hanged and bottom is weighted and moveable in both the in-line (IL) and CF directions, conveying internal fluid flow (IF) and immersed in uniform, and linear shear currents (flows). Our established models are used to conduct a numerical simulation, in which unsteady hydrodynamic forces associated with wake dynamics are described using two van der Pol wake oscillators in both the IL and CF directions that are coupled with the riser. The riser is discretized into a string of spatial slender beam elements, and the wake oscillators are distributed on every immersed element nodes. MATLAB (R2014a) is used to establish a computational program, which is verified using existing experimental data. The lock-in frequency and location are captured by comparing the CF oscillation frequency of the wake model with the CF vibration frequency of the riser at every node of the finite element system when both coincide with each other at the frequency as well as location. The influences of the oncoming flow velocity (OFV), IF velocity (IFV) and bottom hanging weight (BHW) on the lock-in frequency, as well as the lock-in distribution along the riser axis are discussed. In UF, a high IFV (4.5 m/s) makes lock-in occurrence in riser’s “whole oncoming velocity region” in a single-frequency mode but a zero or low IFV (1.5 m/s) makes it null. In linear shear flow, a zero or low IFV (1.5 m/s) makes the lock-in occurrence in riser’s “low and middle oncoming velocity region” in a single-frequency mode and a high IFV (4.5 m/s) makes it in the “whole oncoming velocity region” in the multi-frequency modes, the lock-in frequency mode (but not the lock-in amount) is regardless of OFV and BHW in the context of this paper.

Explorative gradient method for active drag reduction of the fluidic pinball and slanted Ahmed body

We address a challenge of active flow control: the optimization of many actuation parameters guaranteeing fast convergence and avoiding suboptimal local minima. This challenge is addressed by a new optimizer, called the explorative gradient method (EGM). EGM alternatively performs one exploitive downhill simplex step and an explorative Latin hypercube sampling iteration. Thus, the convergence rate of a gradient based method is guaranteed while, at the same time, better minima are explored. For an analytical multi-modal test function, EGM is shown to significantly outperform the downhill simplex method, the random restart simplex, Latin hypercube sampling, Monte Carlo sampling and the genetic algorithm. EGM is applied to minimize the net drag power of the two-dimensional fluidic pinball benchmark with three cylinder rotations as actuation parameters. The net drag power is reduced by 29 % employing direct numerical simulations at a Reynolds number of $100$ based on the cylinder diameter. This optimal actuation leads to 52 % drag reduction employing Coanda forcing for boat tailing and partial stabilization of vortex shedding. The price is an actuation energy corresponding to 23 % of the unforced parasitic drag power. EGM is also used to minimize drag of the $35^\circ$ slanted Ahmed body employing distributed steady blowing with 10 inputs. 17 % drag reduction are achieved using Reynolds-averaged Navier–Stokes simulations at the Reynolds number $Re_H=1.9 \times 10^5$ based on the height of the Ahmed body. The wake is controlled with seven local jet-slot actuators at all trailing edges. Symmetric operation corresponds to five independent actuator groups at top, middle, bottom, top sides and bottom sides. Each slot actuator produces a uniform jet with the velocity and angle as free parameters, yielding 10 actuation parameters as free inputs. The optimal actuation emulates boat tailing by inward-directed blowing with velocities which are comparable to the oncoming velocity. We expect that EGM will be employed as efficient optimizer in many future active flow control plants as alternative or augmentation to pure gradient search or explorative methods.

Portable unmanned surface vehicle that automatically measures flow velocity and direction in rivers

We developed an automatic measurement system for flow velocity and direction in natural rivers using an autonomously controlled unmanned surface vehicle (USV). Oncoming mainstream velocity was measured by the propulsion force required for the USV in order to preserve the position at a measurement point. To conduct such a field mission, the system runs by changing four characteristic control stages: 1) calculation of the tentative propulsion force, 2) navigation to the target point, 3) velocity measurement by staying at the target, and 4) detection of flow direction by flowing downstream. More than 20 indoor tests were conducted under several hydraulic conditions by varying streamwise velocity, and the calibration formula was obtained by interrelating the oncoming velocity magnitude with the propulsion force required to remain at the target. The attitude control was provided with side thrusters to improve the yaw stability of the USV in the oncoming current. The adjunctive work of the side thrusters was very effective. Field tests were conducted to examine the reliability and accuracy of the present automatic flow measurements in a river. Both local velocity and direction in the river flow were measured well by the USV. Error analysis was conducted by comparing with the existing velocimetry results, and the USV was found to possess a sufficient ability to meet practical performance for the flow measurement in a calm river with about 1 m/s velocity.

A weakly nonlinear analytical model for the transversely forced flame describing function of a slit flame

In this work, a weakly nonlinear analytical model of the flame describing function (FDF) of a two-dimensional laminar premixed slit flame subjected to both transverse perturbations and two-dimensional mean flows has been proposed. Two oncoming velocity convection models are used to investigate their effects on the flame tip movements and the nonlinear FDFs. The perturbation method is then used to solve the G-equation. As the flame tip movement plays an important role in the transverse perturbed FDF, its analytical solution is also derived. Validations of these weakly nonlinear solutions are then conducted by comparing them to the previous linear flame transfer function for weak perturbations and results obtained numerically solving the G-equation model. Results show that the transverse oncoming velocity convection models have a significant effect on the nonlinear flame tip dynamics and the nonlinear FDFs, which can also be found in the previous linear model. The transverse nonlinear effects are not so large, as the effect of the transverse perturbation is typically smaller than that of the longitudinal perturbation, which still contributes to reveal the physical mechanisms of the transverse combustion instabilities. For strong transverse perturbations, the analytical solutions of the FDFs derived by the nonlinear model are different from those derived by the linear model both using the uniform model, especially at low frequencies, which indicates that the nonlinear effect is more significant at low frequencies. Transverse mean flow velocity and the amplitude of the transverse disturbed flow velocity can enhance the nonlinearities at low frequencies.

An analytical model for the transversely forced flame transfer functions of conical and V-flame dynamics

Heat release rate perturbations of two-dimensional asymmetric premixed slot flames subjected to transverse perturbations, so called flame transfer functions (FTFs), are theoretically studied in this paper. The proposed models of both the two-dimensional conical flame and V-flame are studied based upon the linear analysis. The flame front dynamic response under the transverse disturbance is captured and solved using the G-equation model. The analytical solution of the FTF is derived using different oncoming velocity perturbation models, in order to reveal the flame heat release rate response mechanism to the transverse disturbances. In the two-dimensional conical flame model, the flame front tip moves with the transverse perturbations, which in turn also affects the FTF. In the two-dimensional V-flame model, the flame front tips are intersected by the flame branches and the unburned gas boundaries; this also contributes to the different behaviours of the FTF. The linear flame tip dynamics and the explicit analytical models of the FTFs of both the conical flame model and the V-flame model are proposed and validated. Results show that the transverse disturbance propagation velocity model has a significant effect on the FTF. The movement of the flame tip is also affected by the transverse convection models.

Numerical Prediction of the Pumpjet Propulsor Tip Clearance Vortex Cavitation in Uniform Flow

Previous studies show that the tip clearance loss limits the improvement of pumpjet propulsor (PJP) performance, and the tip clearance flow field is the most complicated part of PJP flow. In this work, the non-cavitation and cavitation hydrodynamic performances of PJP with a tip clearance size of 1 mm are obtained by using the detached-eddy simulation (DES). At constant oncoming velocity, cavitation first occurs on the duct and then disappears with the decrease of the advance ratio. The rotor blade cavitation occurs at the low advance ratio and comprises tip clearance cavitation, tip leakage cavitation, and blade sheet cavitation. In the rotor region, the typical vortices include tip separation vortex, tip leakage vortex, trailing edge shedding vortex, and blade root horseshoe vortex. Combined with the pressure distribution, both the Q and λ2 criteria give reliable results of vortex identification. The cavitation causes an expansion of tip leakage vortex in the circumferential direction and decreases the intensities of tip separation vortex in the whole tip clearance area and tip leakage vortex in the cavitation area, and enhances the strength of tip leakage vortex in the downstream non-cavitation area.

Passive suction jet control of flow regime around a rectangular column with a low side ratio

A passive jet method was experimentally investigated to manipulate the unsteady vortex shedding around a rectangular column. This method employed a circuit channel connecting the windward and leeward sides of the column to implement the windward passive suction and leeward passive blowing synchronously to modify the flow regime around the column. A bare column model with a side ratio of SR = 1.3 was utilized as a baseline case and the same column models covered with passive suction/jet rings served as controlled cases. Based on different angles of attack (AoAs) of the column models, the Reynolds number varied from 29,300 to 48,200 at an oncoming wind velocity of 10 m/s. At different intervals of suction/jet rings, the surface pressure distributions, aerodynamic forces, and flow structures of the column models were measured to evaluate the control effectiveness of the passive jet method. The results indicated that a notable reduction in the fluctuations of both the surface pressures and aerodynamic forces was achieved. Meanwhile, the mean values of drag forces were also evidently decreased. The flow regime was modified in the vicinity of passive jet holes. The main separation vortices were stretched by the small-scale reverse vortices induced by the jet flow. In addition, the TKE level in the wake flow was considerably decreased in the controlled cases. By extracting eigenvalues and mode coefficients, the POD analysis revealed that the descent of the low-order mode energy corresponded to the suppression of the vortex shedding. The series of phase reconstruction and POD-filtered flow fields demonstrated that the passive jet flow could interact with the shedding vortices and weaken the strength of the vortex shedding process.

Effects of geometrical parameters on the aerodynamic characteristics of a streamlined flat box girder

The effects of aspect ratio (B/D, width to height ratio), wind fairing angle (θ) and relative height of wind nose (H/h, h and H are the distances from the wind nose to the upper and lower surfaces of the girder, respectively) on the aerodynamic characteristics of a streamlined flat box girder were systematically investigated through wind tunnel experiments. A total of 21 cases were tested with B/D = 6, 9 and 12, θ = 45°, 55°, 65° and 75°, and H/h = 1, 2, 3 and 4, which covered most of the typical large span bridges in use. The Reynolds number based on the freestream oncoming velocity U∞ and model height D was 3.3 × 104. The experimental results show that the effects of B/D, θ and H/h are negligible at small wind attack angle (α) with |α| < 4°. The aerodynamic performance of the girder is very sensitive to these geometric parameters at |α| > 4°, which is associated with the states of the flow around the girder. With the increases of |α|, the flow around the girder may transfer from trailing edge vortex shedding (TEVS) to impinging leading edge vortex (ILEV) and leading edge vortex shedding (LEVS). Generally, the girder with H/h = 2–3 and larger B/D and θ corresponds to larger range of α with TEVS, which is favorable to the wind resistance stabilization of the girder.

Identification of flow regimes around two staggered square cylinders by a numerical study

The flow over two square cylinders in staggered arrangement is simulated numerically at a fixed Reynolds number (\(Re =150\)) for different gap spacing between cylinders from 0.1 to 6 times a cylinder side to understand the flow structures. The non-inclined square cylinders are located on a line with a staggered angle of \(45^{\circ }\) to the oncoming velocity vector. All numerical simulations are carried out with a finite-volume code based on a collocated grid arrangement. The effects of vortex shedding on the various features of the flow field are numerically visualized using different flow contours such as \(\lambda _{2}\) criterion, vorticity, pressure and magnitudes of velocity to distinguish the distinctive flow patterns. By changing the gap spacing between cylinders, five different flow regimes are identified and classified as single body, periodic gap flow, aperiodic, modulated periodic and synchronized vortex shedding regimes. This study revealed that the observed multiple frequencies in global forces of the downstream cylinder in the modulated periodic regime are more properly associated with differences in vortex shedding frequencies of individual cylinders than individual shear layers reported in some previous works; particularly, both shear layers from the downstream cylinder often shed vortices at the same multiple frequencies. The maximum Strouhal number for the upstream cylinder is also identified at \({G}^{*}=1\) for aperiodic flow pattern. Furthermore, for most cases studied, the downstream cylinder experiences larger drag force than the upstream cylinder.

Effects of oncoming target velocities on rapid force production and accuracy of force production intensity and timing

ABSTRACTThe present study aimed to clarify the effects of oncoming target velocities on the ability of rapid force production and accuracy and variability of simultaneous control of both force production intensity and timing. Twenty male participants (age: 21.0 ± 1.4 years) performed rapid gripping with a handgrip dynamometer to coincide with the arrival of an oncoming target by using a horizontal electronic trackway. The oncoming target velocities were 4, 8, and 12 m · s−1, which were randomly produced. The grip force required was 30% of the maximal voluntary contraction. Although the peak force (Pf) and rate of force development (RFD) increased with increasing target velocity, the value of the RFD to Pf ratio was constant across the 3 target velocities. The accuracy of both force production intensity and timing decreased at higher target velocities. Moreover, the intrapersonal variability in temporal parameters was lower in the fast target velocity condition, but constant variability in 3 target velocities was observed in force intensity parameters. These results suggest that oncoming target velocity does not intrinsically affect the ability for rapid force production. However, the oncoming target velocity affects accuracy and variability of force production intensity and timing during rapid force production.

Flow control of the wake vortex street of a circular cylinder by using a traveling wave wall at low Reynolds number

Abstract In the present study, a traveling wave wall (TWW) was employed to manipulate the vortex shedding behind a fixed circular cylinder based on a 2-D CFD numerical simulation method at a low Reynolds number of 200. The study mainly focused on four types of TWW propagation directions combined with nine different wave velocities to eliminate vortex shedding, and the lift and drag coefficients and vortex shedding modes at different propagation directions or velocities were analyzed in detail to access the effectiveness of the TWW flow control method. The control mechanism of eliminating wake stemming from the flow around a TWW-controlled circular cylinder was revealed by the boundary vorticity flux (BVF) and relative flow fields. The results show that the type of downstream propagating TWW can effectively eliminate the alternating wake. When the ratio of the wave velocity to the oncoming velocity is 2.0, the fluctuations of the lift coefficients descended to the lowest point. The averages of the drag coefficients decreased with increasing wave velocity and descended to the lowest point when the ratio of the wave velocity to the oncoming velocity was 5.0. Owing to the capture of small-scale vortices, there was a relatively larger level of vorticity in the wave valley of the TWW cylinder. The relative flow fields showed that the vortex shedding from the cylinder was completely eliminated and that the goal of eliminating the oscillating wake and suppressing the potential vortex-induced vibration (VIV) of flow around a cylinder was achieved.

Microphysics of mass-transport in coupled droplet-pairs at low Reynolds number and the role of convective dynamics

Interfacial mass-transport and redistribution in the micro-scale liquid droplets are important in diverse fields of research interest. The role of the “inflow” and the “outflow” type convective eddy-pairs in the entrainment of outer solute and internal relocation are examined for different homogeneous and heterogeneous water droplet pairs appearing in a tandem arrangement. Two micro-droplets of pure (rain) water interact with an oncoming outer air stream (Re ≤ 100) contaminated by uniformly distributed SO2. By virtue of separation/attachment induced non-uniform interfacial shear-stress gradient, the well-defined inflow/outflow type pairs of recirculating eddy-based convective motion quickly develops, and the eddies effectively attract/repel the accumulated outer solute and control the physical process of mass-transport in the droplet-pair. The non-uniformly shear-driven flow interaction and bifurcation of the circulatory internal flow lead to growth of important micro-scale “secondary” eddies which suitably regroup with the adjacent “primary” one to create the sustained inflow/outflow type convective dynamics. The presently derived flow characteristics and in-depth analysis help to significantly improve our understanding of the micro-droplet based transport phenomena in a wider context. By tuning “Re” (defined in terms of the droplet diameter and the average oncoming velocity of the outer air) and gap-ratio “α,” the internal convective forcing and the solute entrainment efficiency could be considerably enhanced. The quantitative estimates for mass entrainment, convective strength, and saturation characteristics for different coupled micro-droplet pairs are extensively examined here for 0.2 ≤ α ≤ 2.0 and 30 ≤ Re ≤ 100. Interestingly, for the compound droplets, with suitably tuned radius-ratio “B” (of upstream droplet with respect to downstream one) the generated “inflow” type coherent convective dynamics helped to significantly augment the centre-line mass flow, which in turn facilitate faster saturation of the upstream droplet. However, for heterogeneous droplet-pairs containing solid nucleus, while increased solid-fraction “S” (the ratio between the radius of the solid nucleus and that of the droplet) through 0.25 ≤ S ≤ 0.45 caused gradual reductions of convective strength and mass absorption rate (RSO2) for the upstream droplet, beyond a critical value S ≥ 0.45 the RSO2 therein continued to rise again owing to the reduced film thickness.

Simulation and analysis on aerodynamic characteristics of deflectable nose

This study uses ANSYS CFX to simulate the aerodynamic characteristics of a rocket-assisted projectile (RAP) with deflectable nose, obtains lift coefficient and drag coefficient with different oncoming airflow velocity, attack angles and deflection angles. The simulation results were verified with experimental data from actual wind tunnel tests. Analysis of the results shows that simulation results vary with nose deflection angle, and how nose deflection affects external ballistics. This research could establish a foundation for further investigations on trajectory control.

An experimental investigation on vortex induced vibration of a flexible inclined cable under a shear flow

In the present study, an experimental investigation was performed to characterize the vortex induced vibration (VIV) of a flexible cable in an oncoming shear flow. The VIV tests were conducted in a wind tunnel with a flexible cable model. It was found that, under different oncoming velocity profiles, the cable model behaved in single-mode and multi-mode VIVs. The displacement amplitudes of the single mode VIVs were found to be larger than those of multi-mode VIVs, and the cross-flow (CF) response was larger than that of in-line (IL) direction for either the single mode or multi-mode VIVs. For a single mode vibration, the largest CF response occurs in the 1st mode VIV, and the motion trajectory of the 1st mode VIV was found to be an inclined figure of eight shape, while other single mode VIVs behaved in ellipse or straight line trajectories. For multi-mode VIVs, no stable vibration trajectories were found to exist since the vibration frequency bands covered two or more vibration modes. The vortex-shedding frequencies in the wake behind the inclined cable were also characterized in the present study. The shedding frequencies of the wake vortices were found to coincide well with the vibration modes: for a single mode VIV, they were close to the dominant vibration mode; for a multi-mode VIV, they could also cover the appearing vibration modes.

Velocity shear flow over rectangular cylinders with different side ratios

Large Eddy Simulation (LES) is carried out to investigate the velocity shear flow over rectangular cylinders with different side ratios of B/D=1, 5 and 8 (B: breadth of the cylinder, D: depth of the cylinder). The shear rate is expressed by a dimensionless shear parameter, defined by the oncoming velocity gradient, the cylinder thickness and the upstream velocity at the center plane of the cylinder. The Reynolds number based on the cylinder depth and the upstream velocity at the center plane of the cylinder is 22,000. Particular attention is devoted to variations with side ratio of shear flow and aerodynamic forces acting on the rectangular cylinders. It is shown that the side-ratio-dependent Strouhal number remains almost unchanged with shear parameter. The shear flow patterns around the rectangular cylinders vary with side ratio, resulting in a side-ratio-dependent aerodynamic force. An interesting finding is that the lift forces on the rectangular cylinders with B/D=5 and 8 act from the high-velocity side to the low-velocity side, while for B/D=1 they act from the low-velocity side to the high-velocity side. The stagnation point moves to the high-velocity side almost linearly with shear parameter for all investigated side ratios, implying that the movement of stagnation point to the high-velocity side is an inherent behavior in shear flow. In addition, the unsteady flow structures and the mechanism for the change of aerodynamic force with side ratio in shear flows are investigated.

Numerical studies on non-shear and shear flows past a 5:1 rectangular cylinder

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

Wind tunnel experiment for wind breakage of Actinidia deliciosa P. shoots

This study investigates the wind-breakage biomechanics of Actinidia deliciosa P. using varying degrees of free-stream turbulence and different physical parameters of plant shoots. Two different turbulent boundary layers (TBL) of wind were simulated inside a wind tunnel test section. The relationship between the load capability and the actual load of shoots was evaluated by using a specific failure criterion. The responses of the shoots to the on-coming wind velocity were estimated quantitatively using three physical parameters: the speedspecific drag, the E-value, and the factor of safety. The E-value of shoots exposed to a highly turbulent condition (TBL type B) is higher than those exposed to a less turbulent one (TBL type A). As the value of the length-diameter ratio (L/D) increases, the peak location of the speed-specific drag shifts towards higher wind speed and the E-value likewise increases. In addition, with increasing L/D, the factors of safety dwindle regardless of wind speed. The trend in the relationship between L/D and the factor of safety for both TBL types is similar.