Accurate estimation of the bleed orifice flow coefficient, which relates bleed plenum pressure to mass flow removed, is important to predicting inlet performance, as well as, estimating bleed drag. Much of the flow coefficient data at conditions of interest to inlet designers is based on bleed plates with multiple rows of holes. The flow coefficient for these plates is typically presented as a function of bleed plenum pressure normalized by the freestream total pressure. Numerical simulations of the flowfield at the entrance of the bleed hole show that the flow is complex, especially for supersonic free stream flow, whereby an alternating expansion/compression wave pattern initiates at the porous bleed surface as the flow turns to enter the hole. This implies that a significant portion of the tangential flow total pressure is given up upon entering a 90° hole. For large aspect ratio (length-to-diameter ratio) bleed holes the effect of the frictional pressure drop is to lower the required plenum pressure to achieve a given mass flow. Conversely, the mass flow will be reduced due to the higher pressure at the start of the duct. Empirical data show that the flow coefficient for supersonic boundary layer bleed holes stops increasing as the plenum pressure to total pressure ratio continues to decrease, indicating that the flow becomes choked. Thus the chocked flow condition helps to make the bleed hole mass flow under these conditions less sensitive or insensitive to the effects of friction caused by the extended hole length. The extent to which this happens is the focus of the current effort, with the paper reporting on experimental and numerical results on flow characteristics and mass flow performance of supersonic bleed holes featuring a range of aspect ratios beyond what has been reported in the past.

A study was done to investigate how boundary layer tripping mechanisms can affect the ability of a permeable surface FW-H solver to predict the far field noise emanating from an airfoil trailing edge. The far field noise in a baseline airfoil as well as the baseline airfoil fitted with fin let fences was analyzed. Two numerical boundary layer tripping mechanisms were implemented. The results illustrated the importance of choosing a permeable integration surface that is outside any high frequency waves emanating from the trip region. The results also illustrated the importance of choosing a boundary layer tripping mechanism that minimizes any extraneous noise so that an integration surface can be taken close to the airfoil.

A breakwater is a structure used to reduce the energy of waves. When used properly, they can protect coasts from being affected by waves. One such application is to lessen erosion along Louisiana’s coastlines, where wave action is strong and is the main source of the erosion. Additionally, the breakwater can change how sediments are transported, and allow for the deposition and accumulation of sediment at target areas. This research aims to give a numerical comparison of the effectiveness of three different breakwater designs, and reveal the turbulence characteristics downstream of the breakwaters. Three breakwaters are examined: a solid panel without any holes, another panel with one hole, and a third panel with three holes. These breakwaters are expected to be placed on the banks of various water bodies in coastal Louisiana, to protect the surrounding wetlands from coastal erosion and land losses. The designs aim to reduce the wave action from the water bodies, while the holes on them allow the sediments to pass through and deposit on the wetlands downstream. To run the simulations, the CFD software ANSYS FLUENT was used. The numerical results were compared to experimental data, and the good agreement proves the accuracy of the results. The effects of different wave patterns on the downstream turbulence were also analyzed and discussed in this study.

The strength of an oil carrier is generally checked using static load or equivalent load of wave action in accordance with relevant specifications. In order to accurately calculate the stress and the deformation of an oil carrier under wave action, the fluid-structure interaction system in the platform Workbench is used in this work. And, the pressure-based solver, the two-phase flow model and UDF (User Defined Function) in the software FLUENT are used to compile the three-order Stokes Wave so as to simulate ocean waves. Forces acting on the surface of the oil carrier are obtained by calculating the flow field, and the structural strength of the carrier is then investigated under sagging and hogging conditions. The results show that: the three-order Stokes Wave matches well with the theoretical result, and it is feasible to research the strength of the oil carrier by generating waves using this numerical method. In addition, the method of fluid-structure interaction is applied to investigate the structural strength of the fully-loaded carrier under sagging and hogging conditions.

Oak Ridge National Laboratory’s (ORNL) Spallation Neutron Source (SNS) uses a mercury target to generate neutrons. When the powerful 1.4 MW, 60Hz proton beam hits the target, a strong pressure wave propagates in the mercury and into the vessel wall due to the rapid temperature rise in mercury. These pressure waves induce cavitation damage on the target container and high stresses, which both limit the lifetime of the target. Since October 2017, helium gas has been injected into the mercury flow in order to mitigate the negative effects of pulse-induced pressure waves. The preliminary strain measurements suggest that gas injection is indeed efficient at mitigating the pressure wave. Tiny nozzles (8-micron diameter) at choked condition are used to generate small bubbles. The bubblers can theoretically inject a total mass flow rate of 0.75 SLPM. However, during operation the bubblers were capable of injecting only approximately 0.45 SLPM, which suggests that some of the nozzles may have become clogged. Since there is a strong desire to inject a larger quantity of gas in the target to, hopefully, mitigate even more the pressure wave, SNS has been looking at implementing swirl bubblers in the target, similar to the ones used in the Japan Proton Accelerator Research Complex (J-PARC) mercury target. In this paper, results with prototypical bubblers tested in water and mercury are presented. Bubblers were installed in prototypical targets and bubble size distributions were measured in both water and mercury. It was found that swirl bubblers can generate a large number of small bubbles, but some compromises were made to keep the pressure losses across them reasonable.

Externally pressurized air journal bearings (air journal EPB’s) are lubrication-free, non-contact bearings that utilize air as the lubrication film. Unlike non-pressurized journal bearings that rely on rotation for hydrodynamic forces, the bearings generate a significant load bearing, restorative, hydrodynamic force independent of rotation. Empirical tests were performed measuring this restorative force and the mass flow out of the bearing-gap as a function of the eccentric displacement of the shaft from the bushing. Two different external pressurization configurations were examined. In one, the bearing-gap was pressurized via two rows of six feedholes located near the ends of the bearings (FH bearings). In the second, the bearing-gap was pressurized via porous liners (PL bearings). The so-called pressure compensation of the bearings was varied by altering the feedhole diameters for the FH bearings and changing the permeability of the PL bearings. The bearing clearance was varied by using shafts of varying OD’s. CFD calculations were then performed to simulate the empirical testing and were found to be in good agreement. The CFD analysis was then expanded over a wide design space for both the FH and PL bearings. The expectation was that the restorative force would continuously increase as the shaft was eccentrically displaced from the bushing reaching its maximum when the shaft was “grounded” so that the shaft contacted the bushing. However, the expanded CFD analysis showed a surprise result as it indicated that there were regions in the design space of the FH bearings where the maximum restorative force occurred at an eccentric displacement that placed the shaft near the bushing but did not ground it. Further eccentric displacement caused a decline rather than the expected increase in the restorative hydrodynamic force indicating a region of negative bearing stiffness . A reference was found that observed bearing load fall off (negative stiffness) with heavily loaded bearings (operating at high eccentricities) similar to our CFD findings. This area of operation was termed the “static instability region”. This paper presents further CFD analysis of the pressure wave in the bearing-gap at varying eccentricities. These waves are graphically dissected to show the characteristics that cause negative stiffness. The results indicate that PL bearings have no static instability and that the area of instability for FH bearings can be predicted.

Recent experimental and modeling studies have indicated that turbulence and cavitation behaviors within a realistic fuel injector have significant effects on the liquid atomization and spray processes. In addition to the breakup process induced by aerodynamic force at the liquid/gas interface, the effects of flow characteristics including turbulence and cavitation inside the injector nozzle on atomization have been shown to be important. The cavitation within the injector is complicated by the turbulent flow under large pressure gradient and geometry of the injector orifice. We have previously developed the “T-blob” and “T-TAB” model, for liquid fuel primary and secondary breakup predictions respectively, to account for liquid turbulence effects within the injector. The objective of this study is to further account for the cavitation effect in the atomization process of a cylindrical liquid jet. In the primary breakup model, the level of the turbulence effect on the liquid breakup depends on the characteristic scales and the initial flow conditions. These scales are further modified to include the cavitation effect. The drop size formed is estimated based on the energy distribution among wave, turbulence and cavitation modes. This paper describes theoretical development of the current model. Both non-evaporating and evaporating spray cases will be investigated to validate the newly developed cavitation-induced atomization model.

A cost-effective test rig is presented that allows for the experimental investigation of supersonic flows for educational purposes. The individual units for the test rig were designed and built by students as part of their degrees. The test rig allows for operating times up to 10 seconds and features a nozzle test section, that can house different test objects. The divergent part of the de Laval nozzle geometry is designed using the method of characteristics for planar two-dimensional supersonic flow. State of the art 3D printing technology has been utilized to manufacture the nozzle geometry. Both optical and pneumatic measurement techniques have been adopted for the current setup. A z-type schlieren setup with two parabolic mirrors is used to perform flow visualization. The entire run can be recorded with a digital high speed camera. Stagnation pressure and temperature are measured in the pressure reservoir. Measurements are used to demonstrate basic thermodynamic effects such as the depressurization of gas-filled pressure vessels. Schlieren photography is used to graphically derive the Mach number and some aspects of Mach waves, oblique shock waves, and expansion waves are discussed. Finally, some effects of surface roughness on the flow field are addressed in this paper. Initial tests with the untreated nozzle geometry led to a fine pattern of very weak oblique shock waves in the supersonic part of the nozzle, that were caused by the finite layer thickness of the printer.

We present a new block-based preconditioner for simulating all-speed compressible flow with phase change. The conservation equations are discretized with a reconstructed Discontinuous Galerkin method and integrated in time with fully implicit time discretization schemes. The resulting set of non-linear equations is converged using a robust Newton-Krylov framework. Due to the stiffness of the underlying physics associated with stiff acoustic waves and viscous material strength effects, we solve for the primitive-variables (pressure, velocity, and temperature). To enable convergence of the highly ill-conditioned linearized systems, we develop a physics-based preconditioner, utilizing approximate block factorization techniques to reduce the fully-coupled 3 × 3 system to a pair of reduced 2 × 2 systems. We demonstrate that our preconditioned Newton-Krylov framework converges on very stiff multi-physics problems with excellent algorithmic and parallel scalability. Results are shown for the classic lid-driven cavity flow problem as well as for 3D laser-induced phase change.

The Louisiana coast experiences significant erosion due to wave actions. There are wetlands and marshes located in the coastal areas, however loss of these wetlands is a major threat. Although coastal waves and floods cause erosion, they do carry sediments, which can potentially counter-act some of the wetland losses. Innovative shoreline protection designs that reduce the wave actions but still allow sediments to travel through could be very beneficial. This research aims to evaluate the effectiveness of the wave reduction and sediment retention of several such designs using CFD simulations. CFD simulations were used to determine the alternations of the wave characteristics and the sediment transport with the designed structures. Small scale experiments of such designs will be conducted in a wave tank facility to validate the modeling results. The research aims to disclose the detailed physics of the flow and sediment transport in this complicated flow-structure interaction problems, and, based on the discoveries, we will provide suggestions to improve the current design to enhance the performance significantly.

The aerodynamic force acting on the pantograph by the airflow is obviously unsteady and has a certain vibration frequency and amplitude, while the high-speed train passes through the tunnel. In addition to the unsteady behavior in the open-air operation, the compressive and expansion waves in the tunnel will be generated due to the influence of the blocking ratio. The propagation of the compression and expansion waves in the tunnel will affect the pantograph pressure distribution and cause the pantograph stress state to change significantly, which affects the current characteristics of the pantograph. In this paper, the aerodynamic force of the pantograph is studied with the method of the IDDES combined with overset grid technique when high speed train passes through the tunnel. The results show that the aerodynamic force of the pantograph is subjected to violent oscillations when the pantograph passes through the tunnel, especially at the entrance of the tunnel, the exit of the tunnel and the expansion wave passing through the pantograph. The changes of the pantograph aerodynamic force can reach a maximum amplitude of 106%. When high-speed trains pass through tunnels at different speeds, the aerodynamic coefficients of the pantographs are roughly the same.

The present work augments vertical-axis unidirectional wave energy converter (WEC) designs with a new approach. The enabling technique is the hydrodynamic design of a special rotor, which consists of a series of uniquely shaped blades in a certain formation. Specifically, individual blades are realized by revolving a two-dimensional symmetric hydrofoil about its chord line. Then the blades are arranged around a vertical shaft in a desired formation to form the rotor. When driven by an approaching flow through interaction, the rotor naturally rotates about the vertical shaft in a predefined direction. The approaching flow could be from any spatial direction, and could have changing speed and direction in any fashion, but the unidirectional behavior of the rotor never changes. Such a behavior guarantees a unidirectional performance of the rotor in waves, where the water flow is omnidirectional and constantly evolving. In validating the proof of concept and characterizing the rotor’s unidirectional performance, experiments were carried out under various flow conditions. Specifically, three types of flows were employed: horizontally oscillating flow, vertically oscillating flow, and orbital flow along a circular path in a vertical plane. The three flows were actually created by translating the rotor in still water, with the first two to characterize the rotor’s responsiveness to the flow direction and the third one to simulate rotor interaction with deep waves. For each flow type, different rotor configurations/blade formations were examined under various testing parameters. For all the cases, the rotor shaft was kept vertically all the time. The experimental results are discussed in details in the paper.

This work presents simulations of a heavy gas, SF 6 , immersed within a light gas, air, under the effect of a converging shock wave. Upon interaction of the shock wave with the perturbed interface between air and SF6, Richtmyer-Meshkov instability (RMI) and, later, Rayleigh-Taylor instability (RTI) take place. More precisely, a succession of RMI and RTI occurs due to multiple shock and rarefaction waves, and gives rise to mixing between the heavy and light fluids. The problem of hydrodynamic instability-induced mixing in converging geometry is particularly relevant to engineering applications such as the process of nuclear fusion by the inertial confinement approach. This study is motivated by the need to better understand the relation between the initial perturbations at the interface between the fluids and the development of the instabilities and mixing in a converging geometry. Using the Flash Code, a PPM hydrodynamic solver developed by the ASC center at the University of Chicago [1], this study focuses on the growth rate of instabilities and the subsequent mixing associated with various carefully designed initial interfacial perturbations in the implosion configuration described above. In cylindrical geometry, comparisons between the growth of high and low frequency single mode perturbations are presented. It is found that at later times, after RMI and RTI take place, the width of the mixing layer is the largest for the low-wavenumber initial interface perturbation. Also, simulations show that the SF 6 target with the highest wavenumber perturbation presents the most mixing at the later times but the lowest wavenumber initial interface perturbation presents the most mixing before reshock.

Unconsolidated reservoirs are notorious for production of sand with crude oil and natural gas. Bed formation in production pipelines poses several operational problems, such as partial or complete pipeline blockage, which decreases production rate and increases frictional pressure losses. Equipment failure may occur as well as erosion/corrosion and formation of corrosive cells under the sand beds. In this study, solid transport in horizontal stratified gas-liquid flow is investigated for a high concentration of 20,000 PPM, leading to sand bed formation. The experiments are conducted with air and water along with glass bead with particle sizes of 45–90 μm and 425–600 μm. The sand bed formation is studied by conducting experiments with gas-slurry flow. The experimental results confirm that the height of the bed decreases with increasing superficial gas velocity, and increases with increasing superficial liquid velocities. It is also observed that the height of the bed created with smaller diameter particles is larger than the one created by the bigger. The acquired experimental data shed more light on the formation of sand beds. It also serves as a basis for theoretical mechanistic models to enable prediction and design of stratified gas-liquid-solid flow.

When a shock wave is incident on an obstacle, it is not only reflected back but also transmitted into the obstacle itself. The transmitted shock wave has not been fully investigated so far, compared with the reflected shock wave. In actual situations, the behavior and the characteristics of the transmitted shock wave are also of importance. In battlefields, human bodies are often subject to explosions and resulting shock waves. In particular, severe damage can be caused when a shock wave is transmitted into the human brain. In the present study, we conducted experiments to investigate the behavior and intensity of a shock wave, after it is transmitted into various materials. The materials used were sintered metal, silicone, and polyethylene foam. They were fixed on a specially devised model with a cavity, by which the resulting wave after a shock wave is transmitted could be observed. In order to understand what is happening in sintered metal, a 2-D model made of straws was devised and used.

In this study, we conducted experiments using a shock tube to investigate how the thickness of soft reflecting material affects the reflected shock wave of oblique shock reflection. Results indicated that transition to Mach reflection (MR) is delayed when the reflecting surface is silicone, compared with that when the surface is rigid. Regarding the influence of reflecting material thickness, no remarkable difference was observed between 1mm and 10mm thickness, due to the trade-off of reflecting wedge angle and material thickness. No significant difference was observed regarding the influence of silicone on wave configuration.

While many theoretical and numerical studies have been carried out to study blast induced traumatic brain injury (bTBI), validation of simulation results is still a concern due to moral issues and experimental constraints. Shock-tubes are one of the major means for replicating blast waves in a controlled medium. North Dakota State University Shock-tube (NDSUST) has been designed to simulate the blast shockwaves in an attempt to study and investigate bTBI. However, accurate replication of a blast profile in terms of the impulse and overpressure is highly dependent on the geometrical features of the shock-tube. To this end, numerical methods such as computational fluid dynamic (CFD) analysis can help to evaluate and increase the efficiency of the current shock-tubes. The NDSUST contains three major parts, namely, driver (the high pressure container), driven cone, and the chamber to setup the head model. The driver and driven cone are separated by layers of Mylar membrane. Shockwaves are defined by three pressure-time characteristics; positive phase (positive impulse), negative phase (negative impulse), and maximum pressure (overpressure). While the current NDSUST simulated most shockwave characteristics accurately, the negative impulse was observed to be considerably long. The diameter of Mylar membrane interface, the volume of the deriver, and the chamber room cross-section connected to the driven cone, were considered as possible parameters affecting the efficiency of the shock-tube. Accordingly, NDSUST was modeled in ANSYS CFX using its actual dimensions. A transient CFD analysis was carried out using ANSYS CFX to simulate the turbulent, supersonic, and compressible flow upon rupture of the Mylar membrane in order to study the pressure wave propagation inside the shock-tube. No-slip boundary conditions were chosen for the shock-tube walls. Driver and driven sections were considered as two separate domains connected using an interface. The shockwave was generated by setting the driver and driven sections at high and low pressures, respectively and running the simulation for a total time of 1 second. The primary results revealed that the current cross-section at the interface of the driven cone and the square chamber caused the pressure disruption (pressure oscillation) upon entrance of the pressure waves into the chamber room. In addition, it was concluded that the driver volume would affect the negative impulse’s duration and the negative peak pressure.

Bioinspired swimming methods have become highly attractive due to the potential for low environmental impact and high efficiency. However, although the efficiency has been quantified for select robotic and theoretical models, this paper explores more directly how requisite power consumption of an undulatory fin is affected by desired swimming speed. It further introduces and quantifies a method for recovering energy from the flow. First, CFD was used to simulate a cross-section of a fish fin with a wave number of 1.2 and a linearly increasing amplitude envelope. Flow speed and fin wave frequency were varied to determine interactive effects on force production and power requirements. The data from these simulations was fitted with polynomial functions over the range used for the study. To determine the potential for power regeneration from the flow, the fin was augmented with a mathematical model of a DC motor and shaft driving it. By incorporating the motor model into the fin analysis, the authors analyzed the amount of power input, or power regeneration, into the system from a constant velocity fluid flow, and developed a relationship between flow velocity and power regeneration. This relationship provides insight into both the level of power regeneration for the fin if held fixed in constant flow, and the minimum flow speed to regenerate energy at a desired rate. The determination of the relationships between efficiency and mode of operation will provide insight into the energetic efficiency of robotic designs using this method. Furthermore, the possibility of power recovery could pave the way for longer lasting underwater robots in extended missions. The determination of both efficiency and power regeneration capability will provide insight into the energetic feasibility of using, and improving on, the current capabilities of bioinspired underwater propulsion.

Blast waves are generated upon release of a large amount of energy in few milliseconds. Upon release, these high pressure waves propagate rapidly and interact with human head and lead to severe traumatic brain injury (TBI). Understanding the mechanics of blast flow would allow us to develop effective tools to protect the head against these shockwaves. Military helmets are known as the most effective tool for protecting the soldier’s head against blast threats. However, due to the complicated nature of the shockwave development and propagation, as well as its interaction with head and helmet, the efficiency of helmets is still in question. The major problem with using helmets under blast loading is the entrapment of blast shockwaves inside the helmet gap and its reflection from the interior of the helmet’s shell. Moreover, development of an amplified pressure region at the opposite side of the incoming blast waves, referred to as the underwash effect of helmets has raised some concerns. To this end, we performed a computational fluid dynamics (CFD) analysis to better understand the mechanism of the blast shockwave interaction with head, as well as the effect of the helmet on the alteration of flow mechanics. The compressible, turbulent blast flow was simulated in ANSYS CFX by releasing the air from a high-pressure domain into the low-pressure one (at ambient pressure). The un/protected heads were exposed to an identical blast overpressure of 520 kPa in a frontal open blast scenario. Pressure contours and velocity profiles were recorded at several time instances for both unprotected and helmeted heads. Our primary results revealed that the change of the flow momentum inside the helmet gap, the reunion of the blast flow inside the gap as well as the development of adverse pressure gradient (and hence recirculating flow region) at the rear side of the head are the major reasons leading to this adverse phenomenon.

In the past decade, the high speed trains (HSTs) in China have experienced a booming development, with the design of CRH380A as a predominant example. A series of brand new HSTs have been developed with high aerodynamic performance, which includes the running resistance, the lift of the trailing car, pressure waves when trains pass by each other, aerodynamic noise in the far field, etc. In order to design HSTs with better aerodynamic performance, it is necessary to perform aerodynamic shape optimization, especially to optimize the streamline shape of HSTs. Parametrization is the basis for the whole optimization process, since good parametrization approach not only affects the optimization strategy, but also determines the design space and optimization efficiency. In the present paper, a series of work related to the streamline shape parametrization performed by the author in recent years have been introduced. Four different parametrization approaches have been exhibited, which are Local Shape Function method (LSF) and Free-Foam Deformation method (FFD), Modified Vehicle Modeling Function method (MVMF), Class function/Shape function Transformation method (CST). These methods could be categorized into two kinds: shape disturbance approach (LSF and FFD) and shape description approach (MVMF and CST). Among these four methods, some are developed by the authors while some are locally modified so as to meet the parametrization of the streamline shape. The detailed process of these four approaches are exhibited in the present paper and the characteristics of these four approaches are compared.