Internal Flow Path Research Articles

CFD를 이용한 굴착용 천공드릴비트의 유로 최적화에 관한 연구

본 연구에서는 드릴비트 내부 유로의 최적설계를 위하여 암분유동해석을 수행하였다. 이를 위해 암분과 기체의 다상유동해석이 가능한 전산유체역학 코드인 Star-CCM+을 사용하였다. 실제 천공시험으로부터 획득한 결과값을 기체 및 암분의 해석조건으로 적용하였다. 내부 유로 설계에 관련된 핵심인자를 3가지로 결정한 후, 다구찌 기법을 활용한 실험계획법으로부터 3가지 설계인자에 대한 최적값을 조사하였다. In this study, a series of CFD (Computational Fluid Dynamics) simulations carried out to evaluate the optimum design model of the internal flow path of drill bit. The Star-CCM+ code was adopted to simulate the multi-phase discharge flow of rock particles and flushing air during a drilling process. The input parameters for the flow simulation of rock particles and air were obtained from the in-situ drilling test results. After the three design factors were determined, the experimental design method (Taguchi method) was utilized to evaluate the optimum value of each factor.

Internal Common-Mode Current Flow Path of Induction Motor

When induction motor is directly driven by PWM power converter, high-frequency common-mode current will be generated inside the motor due to the high-frequency common-mode voltage load. So in this paper, on the basis of the analysis of the coupling effect of the parasitic elements on high-frequency current which include elements between induction motor windings, between the winding and the stator and between the winding and the rotor, According to the structural characteristics of the motor, it is obtained that the parasitic element between the first turns of the stator winding coil and ground can provide low impedance flow path for high frequency common mode current, most of the high-frequency common mode current drain into ground through this path, and the motor stator winding has the uniform transmission line characteristics. The correctness of the conclusions is verified by the experimental results of two different induction motor.

Configuration of hydrological processes in a steep hillslope through causality analysis of soil moisture measurements

AbstractThe vertical and lateral profiles of temporal variations in soil moisture are important for understanding the hydrological process along hillside transects. In this study, relationships among measured soil moistures were explored to configure the hydrological contributions of different flowpaths. All the measured soil moistures included a common stochastic structure because rainfall, the hydrometeological driver, is the main factor that determines the soil moisture response feature, and the infiltration process through the topsoil at a shallow depth is also common in all measured soil moisture histories. Therefore, the relationships between the measured series are also affected by both rainfall and topsoil infiltration. The common stochastic structure of the soil moisture series was removed via a prewhitening procedure. A systematic analysis procedure is presented to delineate the exclusive causal relationships among multiple soil moisture measurements. A monitoring system based on multiplexed time domain reflectometry was used to obtain soil moisture time series along two transects on a steep hillslope during the rainy season. The application of the proposed method for monitoring points in two adjacent locations provided 8, 12, 14, and 13, 16, 22 causal relationships for vertical, lateral in parallel, and diagonal directions, respectively, along the two transects. The point‐based contributions of the internal flowpath can be evaluated as the correlation is normalized in the context of inflow and outflow. The hydrological processes in the soil layer, vertical flow, lateral flow, downslope recharge, and return flow were quantified, and the relative importance of each hydrological component was determined to improve our understanding of the hydrological processes along the two transects of the study area. Copyright © 2011 John Wiley & Sons, Ltd.

Geological discontinuities, main flow path and chemical alteration in a marly hill prone to slope instability: Assessment from petrophysical measurements and borehole image analysis

AbstractClay shale landscapes are sensitive to landslide, erosion, and re‐sedimentation processes. In this context, tectonized clay shales have peculiar hydrological and mechanical behaviours. In order to improve our understanding of the processes involved in such systems, an experimental site has been settled in the Draix Observatory (ORE DRAIX) on a black marl hill slope of the Southern Alps (France) in the framework of the ECOU‐PREF project. The site is a natural laboratory to study the evolution of clay shale landscapes at several scales (regional to µm). In this study, we aim to characterize the internal structure and fissure patterns of a stable interfluve, in order to locate preferential water flows within the system, and anticipate its evolution. This work is based on a series of mutli‐disciplinary approaches including petrophysical analyses, well pulse injection tests and downhole geophysical measurements. Borehole geophysical results were combined with laboratory measurements on core plugs (permeability, density, porosity, and acoustic velocity). Optical and acoustical images have been used as an original tool for internal discontinuities characterisation and potential active flow path detection. They allowed the identification of three main lithological units interpreted as several stages of shale alteration. In addition, several main structural plane discontinuities (open fractures, schistosity planes, and fractures infilled with calcite or clays) were identified from the images and their potential transmissivity discussed with regard to piezometric and tracer measurements. In all, the integration of measurements leads to propose a simple scenario of fluid circulation and chemical alteration of the interfluve. Copyright © 2011 John Wiley & Sons, Ltd.

Whole blood pumping with a microthrottle pump

We have previously reported that microthrottle pumps (MTPs) display the capacity to pump solid phase suspensions such as polystyrene beads which prove challenging to most microfluidic pumps. In this paper we report employing a linear microthrottle pump (LMTP) to pump whole, undiluted, anticoagulated, human venous blood at 200 μl min(-1) with minimal erythrocyte lysis and no observed pump blockage. LMTPs are particularly well suited to particle suspension transport by virtue of their relatively unimpeded internal flow-path. Micropumping of whole blood represents a rigorous real-world test of cell suspension transport given blood's high cell content by volume and erythrocytes' relative fragility. A modification of the standard Drabkin method and its validation to spectrophotometrically quantify low levels of erythrocyte lysis by hemoglobin release is also reported. Erythrocyte lysis rates resulting from transport via LMTP are determined to be below one cell in 500 at a pumping rate of 102 μl min(-1).

LES Predictions of Noise Emissions From a Low-Bypass Ratio Military Gas Turbine Engine

A practical framework for predicting jet structure and noise from military aircraft is described, which is developmental and has been examined for some fundamental jet flow problems. The framework currently utilizes Reynolds-averaged Navier Stokes (RANS) methodology for geometrically complex internal propulsive flowpaths and large eddy simulation (LES) methodology for the jet structure downstream of the nozzle exit. Temporal data from the LES solution is stored on a flared-cylindrical surface surrounding the jet, to be used for noise propagation to the farfield. Earlier applications of RANS methodology combined with the use of analogy-based jet noise codes proved inadequate due to the inability of the noise codes to treat complex 3D flows, such as those associated with multiple nozzles and/or with varied jet noise reduction concepts. Restricting the use of LES (or RANS/LES), methodology to free shear flows remedies the severe grid resolution issues that would be encountered with utilization of LES for modeling internal propulsive flows. The issue of “adequately” initiating the LES solution from a RANS solution profile just downstream of the nozzle exit has been the focus of our exploratory studies and is clearly more complex than standard procedures, such as recycling and rescaling techniques used for simple wall bounded flows. Approaches examined are discussed and unified RANS/LES solutions for several flows are described. The application of this framework to more complex flows requires no fundamental modifications as will also be discussed.

Experimental and Numerical Investigations of Air Cooling for a Large‐Scale Motor

This article experimentally and numerically investigates the thermal performance of a 2350‐kW completely enclosed motor, which is cooled through an air‐to‐air heat exchanger. The air in the heat exchanger includes external and internal flow paths. The external air driven by the rotation of the centrifugal fan goes through the heat exchanger mounted on the top of the frame. The internal air absorbs heat released from the stator and the rotor and then transfers the heat to the heat exchanger through the motion of two axial fans and the rotor. Several test rigs have been set up to measure the performance of the fan and the motor. The Fluent software package is adopted to analyze the complicated thermal‐fluid interactions among the centrifugal fan, two axial fans, heat exchanger, stator, and rotor. The measured data, including the fan performance curves and the temperature profiles of the heat exchanger and the stator, show good agreement with the simulated results. The numerical calculations also show that the nonuniform external flow distribution through the heat exchanger and the air leakage between the axial fan and the rotor reduces the cooling ability of the motor. A detailed discussion is also included to improve the motor cooling performance.

공기 냉각 시스템의 홴 소음 예측 기법

Fan noise prediction method is presented for air conditioning, automobile and electronic cooling system applications where fan acts as an internal equipment having very complicated flow interaction with other various system components. The internal flow paths and distribution in the fan-applied systems such as computer or air conditioner are analyzed by using the FNM(flow network modeling). Fan noise prediction method comprises two models for the discrete frequency noise due to rotating steady aerodynamic lift and blade interaction and for the broadband noise due to turbulent boundary layer and wake vortex shedding. Based on the fan operation point predicted from the FNM analysis results and fan design parameters, the present far noise model predicts overall sound pressure level and spectrum. The predictions for the flow distribution, the fan operation and the noise level in air cooling system by the present method are well agreed with 3-D CFD and actual noise test results.

Experimental Investigation of a Two-Dimensional and a Three-Dimensional Scramjet Inlet at Mach 7

The current experimental study at Mach 7 was carried out to investigate the viscous flow effects in a scramjet inlet with a fixed geometry operating at Mach 7.5-8. To reduce the risk of inlet unstart, an optional passive boundary-layer bleed was integrated at the throat and tested for different bleed dimensions. The passive bleed significantly reduces the lip-shock-induced separation bubble on the ramp. But the correct location of the bleed gap is important for the reduction of the separation bubble. To investigate the compression behavior, different backpressures were applied and the effects on the internal flow structure were analyzed by means of static pressure along the isolator and pitot pressure profiles at the exit of the isolator. Because the reference configuration has a very small internal contraction ratio to guarantee self-starting, the internal compression ratio was increased in three steps by means of additional sidewall compression along the internal flowpath. This includes internal contraction ratios above the starting limit. This measure led to a significant increase of the static pressure ratio at the end of the isolator. The complex flow structures are explained by means of detailed static and pitot pressure plots.

Battery Thermal Management Design Modeling

Battery thermal management is critical in achieving performance and the extended life of batteries in electric and hybrid vehicles under real-driving conditions. Appropriate modeling for predicting thermal behavior of battery systems in vehicles helps to make decisions for improved design and shortens the development process. For this paper, we looked at the impact of cooling strategies with air and direct/indirect liquid cooling. The simplicity of an air-cooling system is an advantage over a liquid-cooling system. In addition to its intrinsically lower heat transfer coefficient, another disadvantage of air cooling is that the small heat capacity of air makes it difficult to accomplish temperature uniformity inside a cell or between cells in a module. Liquid-cooling is more effective in heat transfer and takes up less volume, but the added complexity and cost may outweigh the merits. The surface heat transfer coefficient, h, and the blower power for air cooling are sensitive to the hydraulic diameter of the cooling channel (Dh). However, because of the added thermal resistances, h evaluated at cell surface is not as sensitive to the variation of Dh in an indirect (water/glycol jacket) cooling system. Due to the high heat transfer coefficient at small Dh, direct liquid cooling using dielectric mineral oils may be preferred in spite of high pressure loss in certain circumstances such as in highly transient large heat generating battery systems. In general, air-cooling should be considered first, as the power demand increases with heavier vehicles and more aggressive driving, water/glycol jacket cooling should be considered next. Results of computational fluid dynamics model simulation imply that capturing the internal heat flow paths and thermal resistances inside a cell using a sophisticated three-dimensional cell model is important for more accurate prediction of cell/battery thermal behaviors. This paper identified analyses and approaches that engineers should consider when they design a battery thermal management system for vehicles.

Internal Flowfield Investigation of a Hypersonic Inlet at Mach 6 with Bleed

To study the influence of viscous effects on the performance and, especially the internal flowfield, of scramjet engines, an experimental study has been carried out on a fixed geometry scramjet inlet operating at Mach 6. The tests have been performed using a hypersonic blowdown wind-tunnel facility. To reduce the risk of inlet unstart, a passive boundary-layer bleed has been integrated at the throat and successfully tested. The passive bleed reduces the lip shock-induced separation bubble on the ramp significantly. The obtained experimental results are discussed and compared with computational fluid dynamics calculations. To investigate the compression behavior, different backpressures have been applied and the effects on the internal flow structure are analyzed by means of schlieren change in pitot pressure and calculated Mach number profile base don the geometrical shape of the internal flowpath. The heat transfer coefrficient to the inner sidewall of the isolator is calculated using the time-dependent surface temperature, measured with an infrared system. The variation of the Stanton number based on different flow phenomena could be resolved successfully.

시스템 전자 냉각 팬의 선정 및 소음 평가 기법

Fan selection procedure and fan noise evaluation method are presented for the system electronic cooling by combining FNM(Flow Network Model) and fan noise correlation model. Internal flow paths and distribution in electronic system are analyzed by using the FNM with the flow resistances for flow elements of the system. Based on the fan operation point predicted from the FNM analysis results, the present fan noise model predicts overall sound power, pressure levels and spectrum. The predictions of the flow distribution, the fan operation and the noise level in electronic system by the present method are well agreed with 3-D CFD and actual test results.

Optimisation of Flow Through a Pneumatic Control Valve using CFD Analysis and Experimental Validation

Computational Fluid Dynamics (CFD) is becoming a tool that can be used by engineers to optimise valve performance. CFD is used here to model the fluid flow characteristics through a control valve. By changing various aspects of the internal flow path, the performance of a valve is improved through a greater mass flow rate to optimise its performance. These changes included rounding sharp edges, removing areas of dead-space and moving some internal parts to reduce sharp changes in direction. The CFD model was used to create a new modified design which was then manufactured for testing. The test results were compared to the CFD results from the new model. The CFD and experimental results showed a similar increase in flow rate from the original to the modified valve showing that changes to the internal flow path had a positive effect on the measured flow rate.

Surface and Gas Temperature Measurements Along a Film Cooled Wall

Film cooling is widely used to protect critical sections of propulsion devices from extreme heat loads in the internal flowpath. Many studies have been conducted to formulate scaling laws characterizing the effectiveness of film cooling in a variety of configurations for the development of engineering correlations. There is an emerging demand for detailed measurements near film-cooled surfaces to support computational model development of these complex wall-bounded flows. In this study a unique hot wind tunnel facility was used to perform detailed measurements in a canonical two-dimensional thermally stratified wall-jet configuration. Wall temperature, adiabatic effectiveness, and turbulent flow measurements were performed over a range of carefully controlled inlet conditions. Far-field laboratory effectiveness measurements compare well with previously developed scaling laws; however, the effect of the ratio of mainstream to cooling stream temperature is significantly underpredicted. The micro-thermocouple probe used in this study provided mean flow temperatures and detailed turbulent statistics characterizing the nearwall mixing behavior. The mean flow temperature measurements in the far field demonstrate self-similar behavior whereas fluctuating temperatures indicate fully developed turbulence in the wall layer. The turbulent statistics provided in this study are especially useful for development and validation of computational models of film-cooled surfaces.

Design Optimization of Rocket-Based Combined-Cycle Inlet/Ejector System

The goal of this current research was de termination and optimization of the Rocket Based Combined Cycle (RBCC) Engine inlet/ejector performance trend. For this purposes, a two dimensional rocket -ejector system was studied over a matrix of engine design variables. By pass ratio, ejector compressi on ratio and ejector/mixture thrust efficiency was used to analyze RBCC internal flow path physics. The primary thruster exit flow properties were calculated with the Reacting and Multiphase Program, which was used as fixed inlet conditions for the ejector /mixer analysis. The computational fluid dynamics (CFD) simulations of the inlet/ejector system were carried out with Finite Difference Navier Stokes (FDNS) code. The GO 2/GH 2 combustion physics were solved finite rate with a system of seven species and nin e reactions. The desirability approach of optimization, tied with response surface and neural networks technique has been used for response surface generation and inlet/ejector optimization. An optimum primary thruster size, duct length -to -diameter ratio and ramjet burner to ejector/mixer inlet area ratio are obtained. From this study, it is also noticed that using smaller primary rockets are more effective in reducing the mixing length.

A neural network process model for abrasive flow machining operations

Abstract This paper describes the development of a predictive process modeling system for the abrasive flow machining (AFM) process. This process is used for polishing and surface removal of workpieces with an internal flow path. The core of the process modeling system is a set of neural network models that predicts surface finish and dimensional change. These neural network models are then paired with a heuristic search algorithm to select sets of machine setup parameters for the AFM process. The heuristic search is specifically designed to avoid allowing the neural networks to extrapolate. The completed system was validated using several test pieces, and the results were very promising. The system is currently planned for implementation into the production process. The system has the potential to significantly reduce the development time for new applications of the process and can also be used to suggest alternative machine setup parameters when certain media types are unavailable.

Reappraisal of computer-corrected network analyser design and calibration

A rigorous analysis is carried out of a typical dual-directional coupler network analyser to demonstrate the application of a new circuit analysis technique based on the principle of matrix renormalisation, described in a companion paper, to cascaded multiport networks. The manner in which previously published calibration equations were derived is explained in detail. The analysis is carried out external to the network in terms of voltage excitation and the voltage responses at the accessible ports of the network under mismatched conditions. Each section of the network is represented by a generalised scattering matrix defined in terms of voltage-wave S-parameters with complex normalisation. In this manner, a knowledge of the internal flow paths of the network is unnecessary, in contrast to the flowgraph method employing the nontouching loop rule. The analysis shows that current methods of network analysis, based on the power-flow concept, have given rise to certain misconceptions because source mismatch does not contribute to systematic error-as is generally believed. In addition, these misconceptions appear to have led to the adoption of general design principles for network analysers that are unnecessarily complicated because the effects of mismatches, discontinuities and poor directivity can be completely eliminated by calibration in terms of air-dielectric line standards, provided that all port mismatches are invariant between the reflection and transmission modes of operation.