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Types of running vary from jogging in parks to fast running in competitions. Humans strive for faster, stronger, and more sustainable running performances spanning short to long distances. In the near future, wearable devices will enable humans to run at high speeds and overcome human limits. Therefore, aerodynamic prediction is essential for the system design of a wearable device. This study focused on the aerodynamic drag and flow field according to the assumed human posture at takeoff and touchdown for various running speeds. Numerical simulations were conducted with the Reynolds-averaged Navier–Stokes equation, and a mathematical model, in conjunction with the use of simple geometric models, was developed to predict the aerodynamic drag. In addition, the power and energy were analyzed based on the generated aerodynamic drag. This study demonstrated the theoretical prediction of aerodynamic drag, and estimated the power and energy required to overcome it. The results from this study can be useful in the fields of sports, soft robotics, and biomechanics. Furthermore, the effects of wearable devices attached to the body on the aerodynamic drag can be analyzed by applying the presented methods, and this analysis is beneficial for the optimal design of wearable suits.

Wind energy is a highly effective renewable energy source that can be used to alleviate environmental problems worldwide. However, the variability of wind inhibited the development of wind power generators such as limited directional conditions, restrictions pertaining to the installation sites, occurrence of mechanical failures, and limited wind speed ranges. In here, to overcome these limitation, we developed a stackable disk-shaped wind-rolling triboelectric nanogenerator (DWR-TENG) to generate energy from omnidirectional wind. Its disk-shaped design ensures that the device does not involve any restrictions related to the wind direction or installation. Furthermore, lightweight charged spheres in the device can reduce the occurrence of mechanical failures and expand the wind speed range (operating in 6.5–17.5 m/s) for the generator operation. The performance of the DWR-TENG was evaluated considering various design parameters by conducting experiments and an FEM simulation. Specifically, the DWR-TENG can be easily stacked in several layers, thereby exhibiting an enhanced charging efficiency.

Conventional practice includes a limited depiction of urethral pressure and flows based on fragmented gross clinical observations. However, with technological advancements in simulations, computational fluid dynamics (CFD) can provide an alternative approach to predict the bladder pressure with a concordant quantitative flow field in the urethra. Thus, this study aims to comprehensively analyze the urine flow characteristics in various urethra models using simulations.Three-dimensional urethra models were constructed for seven specific subjects based on clinical radiographs. Simulations with Reynolds averaged Navier-Stokes model were performed to quantitatively investigate the urine flow under various volume flow rate of voided urine.Under benign prostatic hyperplasia, the spindle shape of the prostatic urethra (PRU) generates wake flow. The wake flow was also observed in several regions downstream of the PRU, depending on the urethra shape. This wake flow resulted in total pressure loss and urinary tract dysfunction. When comparing pre- and post-operative urethra models, the bladder pressure decreased by 14.98% in P04 and 4.67% in P06. Thus, we identified variability between surgical results of patients. The bladder pressure according to the volume flow rate of voided urine was investigated using simulations and the theoretical consideration based on hydrodynamics. In theoretical consideration, the bladder pressure was expressed as a second-order polynomial for volume flow rate. These results concur with the simulation results.Numerical simulation can describe the urine flow field in the urethra, providing the possibility to predict the bladder pressure without requiring painful, invasive interventions, such as cystoscopy. Furthermore, effective treatments to improve urination function can be formulated to be patient-specific, by detecting causes and problem regions based on quantitative analysis and predicting post-surgical outcomes.

The forward expansion hole improves the film cooling effectiveness by reducing the penetration of the coolant jet into the main flow compared to the cylindrical holes. In addition, compound angles improve the film cooling effectiveness by promoting the lateral spreading of the coolant on a wall. Evidently, the combination of a compound angle and shaped hole further improves the adiabatic film cooling effectiveness. The film cooling flow with a shaped hole with 15° forward expansion, a 35° inclination angle, and 0° and 30° compound angles at 0.5 and 1.0 blowing ratios was numerically simulated with Large Eddy Simulations (LES) and Reynolds-averaged Navier–Stokes (RANS) simulations. The results of the time-averaged film cooling effectiveness, temperature, velocity, and root-mean-square (rms) values of the fluctuating velocity and temperature profiles were compared with the experimental data by Lee et al. (2002) to verify how the LES improves the results compared to those of the RANS. For the forward expansion hole, the velocity and temperature fluctuations in the LES contours are smaller than those of the cylindrical hole; thus, the turbulence and mixing intensity of the forward expansion hole are weaker and lower than those of the cylindrical hole, respectively. This leads to the higher film cooling effectiveness of the forward expansion hole. By contrast, the RANS contours do not exhibit velocity or temperature fluctuations well. These results are discussed in detail in this paper.

Progression of carotid stenosis (CS) significantly reduces blood flow in the affected arteries and alters both proximal and distal hemodynamics. While conventional studies consider only the stenosis region for analysis, an extended larger arterial domain of aortic–cerebral vasculature is used to avoid artificial modeling of the inlet condition to the carotid region and facilitate automatic flow redistribution during CS progression. The fluid domain was constructed and simulated using an open-source package SimVascular, and three patient models with five stenosis cases each were created using medical images. Newtonian, incompressible, and rigid-wall conditions were assumed because of the high computational burden, and boundary conditions of the lumped Windkessel and pulsatile flow rate were implemented for the outlets and inlet, respectively. We present a novel index called circulation core fraction (CCF) to quantify and visualize the stenosis-driven hemodynamics; the CCF is developed from the benchmark backward-facing step problem and compares the representative recirculation to the total volume. Thus, CCF in the post-stenotic region increases during CS progression regardless of patient-specific features whereas that in the pre-stenotic region exhibits patient-specific nature despite the incremental tendency. Streamlines with custom sources show a helical vortex with recirculation and artery-wise flow streams that vary during CS progression. We also report transitional patterns in both the pulsatility index (PI) contours and Q-criterion, where the PI values shift from high–low–high to high–low–low across the stenosis, and the latter is nearly absent at 0% and 95% but mostly present at 50% and 75% CS.

We investigated the effects of atherosclerosis in the carotid region on cerebral haemodynamics. A total of 15 stenosis cases following NASCET criteria were modelled using patient-specific medical image data and an open-source package, SimVascular. The formulation adopted the stabilised Petrov–Galerkin scheme with Newtonian and incompressible assumptions. The boundary conditions employed pulsatile inflow and three-element lumped Windkessel outlet conditions with a rigid wall assumption. We present transitions in the represented CoW during stenosis progression using three-dimensional aortic-cerebral vasculature for the first time. This was driven by the conserved total cerebral blood flow to 50% carotid stenosis (CS) (P-value, P > 0.05), which deteriorated during subsequent stages of CS (P < 0.01), and the effective collateral capability of the communicating arteries (CoAs) activated from a degree of 75% and above (P < 0.0001). The prevalence of ‘complete’ CoW peaked at 50% CS and then declined. Despite the collateral flow, the ipsilateral hemispheric perfusion was moderately reduced (P < 0.01), and the contralateral perfusion was conserved (P > 0.05), revealing the ineffectiveness of collateral capability of CoW at the extreme stages of CS. We identified bulk cerebral auto-regulation effects of the conventional Windkessel model, demonstrating accurate flow reduction in the stenosed artery.

The present study numerically investigated the three-dimensional turbulent flow and heat transfer characteristics of longitudinal vortices embedded in a turbulent boundary layer in a bent channel and examined the effects of a spanwise pressure gradient on the distortion of the turbulent boundary layer. The commercial code (ANSYS Fluent v17.0) was used for the simulation with the Reynolds stress model (RSM) to consider anisotropic effects. The simulation results showed that an asymmetric distortion of the turbulent boundary layers and a substantial change in the vortex shape were caused by the presence of an additional mean shear rate, originated from the spanwise pressure gradient. It was also found that an increase in the spanwise pressure gradient contributed to an enhancement of production of turbulent kinetic energy, resulting in stronger mixing flows. In particular, the Stanton number had an asymmetric distribution mainly in the bent region where the spanwise pressure gradient was dominant.

In this study, numerical simulations were conducted at various pod speeds ( v p o d = 100–350 m/s) using an unsteady, compressible solver with the Reynolds-averaged Navier–Stokes model to analyze the aerodynamic characteristics and pressure wave behavior in the Hyperloop system. Furthermore, the aerodynamic drag and pressure wave behavior were theoretically predicted based on quasi-one-dimensional assumptions. The flow around the pod is classified into three regimes according to the pod speed based on the compressible flow phenomena. In regime 1 ( v p o d = 100–170 m/s), the compression waves develop into normal shock waves even without the occurrence of choking at the throat. In regime 2 ( v p o d = 180–230 m/s), choking occurs at the throat and an oblique shock wave appears within the pod tail section. In regime 3 ( v p o d = 240–350 m/s), a trailing shock wave propagates at the end of the oblique shock wave. Due to fully accelerated flow in this regime, the Mach number of the flow behind the pod in a pod-fixed coordinates remains constant as 2.1, regardless of the pod speed. This constant Mach number causes the drag coefficient to decrease while the pod speed increases. Although non-isentropic conditions such as the formation of a boundary layer and flow separation cause variation between the theoretical prediction and simulation results, the predicted properties of the pressure waves and the aerodynamic drag of the pod concur with the simulation results. Because the boundary layer along the pod is thinner at a higher pod speed, the difference between the theoretical and simulation values of the leading shock pressure decreases from 9.71% to 2.83% and that of the leading shock speed decreases from 4.39% to 1.30% as the pod speed increases from 180 to 350 m/s. Additionally, the theoretically predicted drag of the pod shows good agreement with the simulation results with an error of around 6%.

The Hyperloop system is a new concept that allows a train to travel through a near-vacuum tunnel at transonic speeds. Aerodynamic drag is one of the most important factors in analyzing such systems. The blockage ratio (BR), pod speed/length, tube pressure, and temperature affect the aerodynamic drag, but the specific relationships between the drag and these parameters have not yet been comprehensively examined. In this study, we investigated the flow phenomena of a Hyperloop system, focusing on the effects of changes in the above parameters. Two-dimensional axisymmetric simulations were performed in a large parameter space covering various BR values (0.25, 0.36), pod lengths (10.75–86 m), pod speeds (50–350 m/s), tube pressures (~100–1000 Pa), and tube temperatures (275–325 K). As BR increased, the pressure drag was significantly affected. This is because of the smaller critical Mach number for a larger BR. As the pod length increased, the total drag and pressure drag did not change significantly, but there was a considerable influence on the friction drag. As the pod speed increased, strong shock waves occurred near the end of the pod. At this point, the flows around the pod were severely choked at both BR values, and the ratio of the pressure drag to the total drag converged to its saturation level. At tube pressures above 500 Pa, the friction drag increased significantly under the rapidly increased turbulence intensity near the pod surface. High tube temperatures increase the speed of sound, and this reduces the Mach number for the same pod speed, consequently delaying the onset of choking and reducing the aerodynamic drag. The results presented in this study are applicable to the fundamental design of the proposed Hyperloop system.

Arterial tonometry is a widely used non-invasive blood pressure measurement method. In contrast to the cuff-based method, it is possible to obtain a continuous pressure profile with respect to systolic and diastolic pressures using this method. However, due to a requirement of arterial tonometry-that a sensor needs to be placed directly above a blood vessel-placement error is inevitable if the measurement device is only capable of measuring local regions. This study assumed that the plate sensor is flexible, thus reducing the placement error. We investigated the pressure distribution along the wrist surface rather than the local region through the contact simulation between the flexible plate sensor and the wrist. As a result, we concluded that there is a unique pressure distribution for any specific wrist, regardless of the length and position of the plate, and that it is possible to measure the blood pressure using the response at the wrist surface to the pressure inside the radial artery.

We present a novel reaction analogy (RA) based forcing method for generating stationary scalar fields in incompressible turbulence. The new method can produce more general scalar PDFs (e.g. double-delta) than current methods, while ensuring that scalar fields remain bounded. Such features are useful for generating initial fields in non-premixed combustion or for studying non-Gaussian scalar turbulence. The RA method mathematically models hypothetical chemical reactions that convert reactants in a mixed state back into its pure unmixed components. Various types of chemical reactions are formulated and the corresponding mathematical expressions derived such that the reaction term is smooth in the scalar space and is consistent with mass conservation. For large values of the scalar dissipation rate, the method produces statistically steady double-delta scalar PDFs. Quasi-uniform, Gaussian, and stretched exponential scalar statistics are recovered for smaller values of the scalar dissipation rate. The shape of the scalar PDF can be further controlled by changing the stoichiometric coefficients of the reaction. The ability of the new method to produce fully developed passive scalar fields with quasi-Gaussian PDFs is also investigated, by exploring the convergence of the third order mixed structure function to the "four-thirds" Yaglom's law., Published in Physical Review Fluids

Solutions from inviscid linear stability theory (LST) and linear parabolized stability equations (PSE) were used to quantify the extent to which instability waves represent actual near-field dynamics in high-speed forced turbulent jets. The mean and unsteady flow data were taken from a well-validated large-eddy simulation (LES) database (Bodony and Lele, 2005). The jets and their operating conditions were heated high subsonic ( M j = 0.97, T j/ T∞ = 2.3, Re D = 84,000) and unheated supersonic ( M j = 1.95, T j/T∞ = 0.56, Re D = 336,000) jets with the same jet exit velocities. The coherent components of the turbulent jet flow fields were extracted using a filter based on proper orthogonal decomposition (POD). To examine the effects of nonlinear interactions and to test the decomposition method, forced laminar jets were also considered; the flow data were obtained from a direct numerical simulation (DNS) database for an unheated M j = 0.90 and Re D = 4,100 jet (Ryu, 2010). Two methods were used to extract instability waves from the nonlinear flow fields: first, bi-orthogonal relations between regular and adjoint instability waves were formulated from linearized Euler equations to determine the amplitude coefficients of the instability waves in nonlinear flows; then, a least-squares fit was applied to solutions from the PSE, POD, and LES data for the same purpose. The noise radiated by the deduced instability wave modes, POD, and LES were computed using the Kirchhoff surface integral method. Frequencies St = fD j/ U j = 0.1 ∼ 0.5 at azimuthal modes m = 0, 1, and 2 were compared. The adjoint decomposition method showed promising results only for the laminar jet. The eigenfunction shape in the radial direction and the growth and decay of energy in the streamwise direction were well captured. However, this method produced errors in analyses of turbulent jets due to sensitivity in regions where the mode had saturated and was decaying. The results of PSE and POD showed reasonably good agreement in the near field for the first helical mode ( m = 1). However, there was only limited agreement in the far field, and among other modes, in contrast to the good agreements described in recent studies for supersonic unforced jets. This is due to the strong nonlinear effects in forced turbulent jets considered in the present study. This finding confirms a limitation of linear stability theories when predicting the wavepacket dynamics of forced turbulent jets. The PSE solution for the subsonic jet showed very weak acoustic radiation, and the far-field noise displayed strong sensitivity to the location of the Kirchhoff surface. This suggests a limitation of direct propagation approaches for the PSE solutions of moderately heated subsonic jets.

The interaction of a shock wave with quasi-vortical isotropic turbulence (IT) represents a basic problem for studying some of the phenomena associated with high speed flows, such as hypersonic flight, supersonic combustion and Inertial Confinement Fusion (ICF). In general, in practical applications, the shock width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS) (Ryu and Livescu, J Fluid Mech 756:R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). Using LIA to alleviate the need to resolve the shock, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here, such results with Taylor Reynolds number approximately 180 are used to investigate the changes in the vortical structure as a function of the shock Mach number, $$M_{s}$$ , up to $$M_{s}=10$$ . It is shown that, as $$M_{s}$$ increases, the shock interaction induces a tendency towards a local axisymmetric state perpendicular to the shock front, which has a profound influence on the vortex-stretching mechanism and divergence of the Lamb vector and, ultimately, on the flow evolution away from the shock.

Background: Distal radius fractures (DRFs) are 16% of fractures treated by orthopedic surgeons. Obesity’s influence on DRF complexity has not been studied. This study was undertaken to determine if body mass index (BMI) affects DRF pattern, treatment, and functional outcomes. Methods: Part 1 was a retrospective review of patients who sustained a DRF after a fall from standing height with no prior reduction or treatment. Radiographs were classified as “simple” or “complex.” Part 2 consisted of contacting patients from Part 1 and obtaining a Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) score. Retrospective review also identified patients who failed initial nonoperative treatment. Fracture pattern, failure of nonoperative treatment, and QuickDASH scores were compared with BMI at the time of injury. Results: For Part 1, 130 patients (132 wrists) were identified. Average age was 57 years, 77% were female, and average BMI was 28.2 kg/m2. Each point increase in BMI increased the chance of having a complex DRF (odds ratio = 1.07). Part 2 identified 50 patients who completed a QuickDASH at an average of 4.6 years after injury. Those with a BMI 2 (n = 15) had an average QuickDASH score of 37; patients with a BMI ≥25 kg/m2 (n = 35) had an average QuickDASH score of 18. Increasing BMI was suggestive of a lower QuickDASH score ( P = .08). No significant difference was found with respect to BMI and failure of nonoperative treatment. Conclusions: A higher BMI increases the odds of a complex DRF. Despite more complex fractures, overweight patients may experience less disability after sustaining a DRF.

Near-field characteristics of supersonic wave components in turbulent jets are investigated using the well-validated large eddy simulation (LES) database by Bodony and Lele (2005) [1] . Three unheated (constant stagnation temperature) jets with a jet Mach number ranging from 0.51 to 1.95, and one heated ( T j / T ∞ = 2.3 ) transonic jet are considered. The Reynolds number based on the exit diameter ranges from 79,000 to 336,000. The supersonic wave components of the flow variables are decomposed from the full flow-field using wavenumber–frequency domain filtering. The spatial structure of the fluctuating pressure field is obtained by the proper orthogonal decomposition (POD) of the full and filtered data. POD modes of unheated subsonic jets reveal large scale-disparity between the full and supersonic components. For the supersonic jet at M j = 1.95 , the energetic structures of the pressure field also contribute significantly to the supersonic components, and scale disparity is absent. The variance of the subsonic pressure components from unheated jets scales as U j 4 , where U j is the jet exit velocity (i.e., | p ˜ 2 | ~ U j 4 ), which is the expected scaling for turbulence-associated hydrodynamic-pressure fluctuations. In contrast, supersonic pressure variance, which peaks within the turbulent flow region, scales with U j 8 , coinciding with the far field noise intensity scaling associated with Lighthill׳s analogy. In the acoustic near-field, even higher exponent of the jet velocity scaling is found for the positive phase velocity supersonic pressure component ( | p ˜ 2 | ~ U j 10 ) , which is consistent with the scaling of the far-field noise at shallow exit angles [2] , [3] . The filtered velocity components also show a similar pattern, i.e., supersonic velocity variances scale with a higher power of the jet velocity, but the scaling exponents in jet-region are different for different velocity components and depend on the azimuthal mode. Previous investigations have presented two distinct spectral peaks due to the hydrodynamic and acoustic pressure components in the near-acoustic field. Using filtered components, it is found that density and velocities also show such clear hydrodynamic to acoustic transition, albeit with different transition points. The strongly directive noise radiation from subsonic jets is explained using POD projection of supersonic disturbances.

Peripheral nerve injuries affect all age groups and can be devastating to patients. A timely repair and thorough exam both preoperatively and intraoperatively can help increase the chances of a successful outcome. The technical aspects of peripheral nerve injury evaluation and repair must take into account the unique anatomy and function of the nervous system. Proper microsurgical techniques such as tension-free repair are a critical aspect of the repair process. Nerve grafts, conduits, and biotherapies are all viable ways to increase the odds of a meaningful repair. Proper immobilization, mobilization, and a targeted rehabilitation protocol are also important.

Results from recent LES studies of high-speed jet flows and its near and far-field noise (Mendez et al. AIAA2010-271) are reviewed with an emphasis on validation of the LES results. Far-field noise is predicted using data collected on a conical FW-H surface. Very good agreement with the measurement reported by Bridges & Wernet (AIAA-2008-2834) is observed. Data analysis of the flow disturbances within the jet and in the near-field is used to better characterize the sound source processes. We analyze LES data of Bodony and Lele (Phys. Fluids, vol. 46, 2005) using a filter in the wavenumber-frequency domain. The supersonic components of pressure and radial velocity fluctuation show peaks within the jet and show the U j 8 scaling behavior consistent with the far-field radiated j noise levels. The observed scaling is also consistent with a perturbation expansion of nearly incompressible turbulent fluctuations within the jet flow. Linear global mode analysis of the non-parallel jet mean flow is performed. Features of Mach wave radiation are evident in the global modes for supersonic convection. Large transient growth is found due to convective non-normality. Some implications of this analysis for jet noise modeling are discussed.