Three-dimensional Viscous Flow Analysis Research Articles

양배수용 사류펌프 내 삼차원 유동에 대한 수치적 연구

In this paper, numerical study on a mixed-flow pump for irrigation and drainage has been performed based on three-dimensional viscous flow analysis. Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are discretized by finite volume approximations and solved by the commercial CFD code ANSYS CFX-11.0. A structured grid system is constructed in the computational domain, which has O-type grids near the blade surfaces and H/J-type grids in other regions. The numerical results were validated with experimental data for the heads and efficiencies at different flow coefficients. The efficiency at the design flow coefficient is evaluated with the variation of two geometric variables related to area of discharge and length of the vane in the diffuser. The results show that efficiency of the mixed-flow pump at the design flow coefficient is improved by the modifications of the geometry.

Inner Workings of Shrouded and Unshrouded Transonic Fan Blades

This paper reports on the numerical assessment of the differences in aerodynamic performance between part span shrouded and unshrouded fan blades generally found in the first stage of multistage fans in low bypass ratio aircraft engines. Rotor flow fields for both blade designs were investigated at two operating conditions using a three-dimensional viscous flow analysis. Although designed to the same radius ratio, aspect ratio, and solidity, the unshrouded fan rotor had a slightly increased tip speed (+3%) and somewhat lower pressure ratio (−3.2%) due to engine cycle requirements. Even when allowing for these small differences, the analysis reveals interesting differences in the level and in the radial distribution of efficiency between these two rotors. The reason for the improved performance of the shrouded rotor in part can be attributed to the shroud blocking off the radial migration of boundary layer fluid centrifuged from the hub on the suction side. As a result, the shock boundary layer interaction seems to be improved on the shrouded blade. At the cruise condition, the efficiency is the same for both rotors. The slightly better efficiency of the shrouded blade in the outer panel is nullified by the large efficiency penalty in the vicinity of the shroud. As there is no significant radial migration of fluid in the suction side boundary layer, as indicated by the analysis at this condition relative to the design speed case, the benefit due to the shroud is greatly reduced. At this speed and at lower speeds, the shroud becomes a net additional loss for the blade. Also of interest from the numerical results is the indication that significant blade ruggedization penalties to performance can be reduced in the case of the unshrouded blade through custom tailoring of its mean camber line.

Study on Secondary Flow within Low Aspect Ratio Steam Turbine Cascade (1st Report, Mechanism of Loss Generation)

In order to address recent environmental problems such as global warming due to CO2, emissions, continuous efforts are required to improve the performance of the steam turbine, which supports the base of energy conversion. Although the aerodynamic design technologies of steam turbine have been developed remarkably by applying the computational fluid dynamics (CFD), it is not easy to reduce the losses within a low aspect ratio cascade in the control stage and high-pressure stages even if the latest three-dimensional design are used. Then, the authors investigated the loss generation mechanism in a low aspect ratio cascade using the smoke visualization and detailed internal flow measurement with a micro pitot probe to develop the new technologies for reducing the secondary loss. This paper describes the evolution of horse-shoe vortex and passage vortex through a turbine blade in experimental studies, theoretical approach to explain the motion of the vortex and the effects of inlet boundary layer on passage vortex interaction analyzed by three-dimensional viscous flow analysis.

Computational study of effect of tabs on a jet in a cross flow

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier–Stokes code for the case of a jet in a cross flow with a delta tab placed on the windward side of the jet to inhibit mixing for film cooling applications. The flow configuration which was previously studied experimentally, involved a jet discharging normally from the floor of the wind tunnel test section into the cross flow with a momentum ratio (jet/cross-flow) of 36. The computed results are compared with the experimental data which include streamwise velocity and vorticity distributions at various axial locations downstream of the jet. The computational results show reasonably good agreement with the experimental data.

Internal flow analysis of nozzles for DI diesel engines using a cavitation model

A three-dimensional viscous flow analysis method using a cavitation model was applied to run internal flow calculations for the fuel injector nozzles of direct-injection diesel engines. It is especially notable that this method made it possible to examine and clarify the mechanism producing an asymmetrical spray from the valve covered orifice type nozzle under a small lift condition with an eccentric needle position. The calculated results for cavitation were compared with experimental data obtained by using a transparent model scaled up fivefold, and good qualitative agreement was seen between the two sets of data.

Flow Cytometric Analysis by Using Micro-Machined Flow Chamber.

Effect of the flow characteristics in a newly developed micro-machined sheath flow chamber on the accuracy of cytometric analysis was investigated. The chamber was formed by laminating three 100-μm-thick photo-etched metal plates. Sample fluid containing cells, which enters the chamber via an axial specimen nozzle, is enveloped by a buffering sheath-fluid and transported to a capillary channel. Microscopic observation and three-dimensional viscous flow analysis predict that the dispersion of cells in the capillary channel is favorably reduced when the Reynolds number is between 500 and 750, which is value associated with low deviation of the analytical results. The five classifications of human white blood cells were determined. and this verified that change of the deviation depends on the Reynolds number. The results confirm Reynolds number of 500-750 is appropriate for good classification.

Design and Testing of Swept and Leaned Outlet Guide Vanes to Reduce Stator–Strut–Splitter Aerodynamic Flow Interactions

Large circumferentially varying pressure levels produced by aerodynamic flow interactions between downstream stators and struts present a potential noise and stability margin liability in a compression component. These interactions are presently controlled by tailoring the camber and/or stagger angles of vanes neighboring the fan frame struts. This paper reports on the design and testing of a unique set of swept and leaned fan outlet guide vanes (OGVs) that do not require this local tailoring even though the OGVs are closely coupled with the fan frame struts and splitter to reduce engine length. The swept and leaned OGVs not only reduce core-duct diffusion, but they also reduce the potential flow interaction between the stator and the strut relative to that produced by conventional radial OGVs. First, the design of the outlet guide vanes using a single blade row three-dimensional viscous flow analysis is outlined. Next, a two-dimensional potential flow analysis was used for the coupled OGV–frame system to obtain a circumferentially nonuniform stator stagger angle distribution to reduce the upstream static pressure disturbance further. Recognizing the limitations of the two-dimensional potential flow analysis for this highly three-dimensional set of leaned OGVs, as a final evaluation of the OGV–strut system design, a full three-dimensional viscous analysis of a periodic circumferential sector of the OGVs, including the fan frame struts and splitter, was performed. The computer model was derived from a NASA-developed code used in simulating the flow field for external aerodynamic applications with complex geometries. The three-dimensional coupled OGV–frame analysis included the uniformly staggered OGV configuration and the variably staggered OGV configuration determined by the two-dimensional potential flow analysis. Contrary to the two-dimensional calculations, the three-dimensional analysis revealed significant flow problems with the variably staggered OGV configuration and showed less upstream flow nonuniformity with the uniformly staggered OGV configuration. The flow redistribution in both the radial and tangential directions, captured fully only in the three-dimensional analysis, was identified as the prime contributor to the lower flow nonuniformity with the uniformly staggered OGV configuration. The coupled three-dimensional analysis was also used to validate the design at off-design conditions. Engine test performance and stability measurements with both uniformly and variably staggered OGV configurations with and without the presence of inlet distortion confirmed the conclusions from the three-dimensional analysis.

Computation of Three-Dimensional Compressible Flow From a Rectangular Nozzle With Delta Tabs

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration, which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics is examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.

Finite Element Error Analysis Approach for Three-Dimensional Incompressible Viscous Fluid Flow Analysis

In our previous research, the modified Galerkin method was proposed as one of the most efficient methods for the analyses of convection-diffusion problems and two-dimensional viscous fluid flow problems. In this modified Galerkin method, the inertia term is considered explicitly, so only the symmetrical matrixes appear. Then an artificial viscosity is introduced through an error analysis approach to improve its accuracy and stability. In this paper, we proposed a new finite element formulation for three-dimensional incompressible viscous fluid flow analysis. This formulation (‘MS’ algorithm and ‘MSR’ algorithm) is based on the modified Galerkin method coupled with the Semi-Implicit Method for Pressure-Linked Equations. The cubic cavity flow problems were investigated for the Reynolds number of 400, 1,000, 2,000 and 3,200 using non-uniform meshes. Finally, we confirmed the effectiveness of our proposed method through the comparison with other research works.

Flow Cytometric Analysis by using Micro-Machined Flow Chamber.

Effect of the flow characteristics in a newly developed micro-machined sheath flow chamber on the accuracy of cytometric analysis was investigated. The chamber was formed by laminating three 100-μm-thick photo-etched metal plates. Sample fluid containing cells, which enters the chamber via an axial specimen nozzle, is enveloped by a buffering sheath-fluid and transported to a capillary channel. Microscopic observation and three-dimensional viscous flow analysis predict that the dispersion of cells in the capillary channel is favorably reduced when the Reynolds number is around 500∼750, which is value associated with low deviation of the analytical results. The five classifications of human white blood ceils were determined, and this verified that change of the deviation depends on the Reynolds number. The results confirm Reynolds number of around 500∼750 is a appropriate for good classification.

Inner Workings of Aerodynamic Sweep

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single-stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft swept adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the tip, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

3-D Navier-Stokes analysis of crossing glancing shocks/turbulent boundary layer interactions

Three-dimensional viscous flow analysis is performed for a configuration where two crossing and glancing shocks interact with a turbulent boundary layer. A time marching 3-D full Navier—Stokes code, called PARC3D, is used to compute the flow field and the solution is compared to the experimental data obtained at the NASA Lewis Research Center 1 ft × 1 ft supersonic wind tunnel facility. The study is carried out as part of the continuing code assessment program in support of the Generic Hypersonic Research at NASA Lewis. Detailed comparison of static pressure fields and oil flow patterns is made with the corresponding solution on the wall containing the shock/boundary layer interaction in an effort to validate the code for hypersonic inlet applications.

Three-Dimensional Viscous Flow Analysis of an Advanced Ducted Propeller Subsonic Inlet

A time-marching Navier-Stokes code called PARC3D was used to study the three-dimensional viscous flow associated with an advanced ducted propeller (ADP) subsonic inlet at takeoff operating conditions. At a freestream Mach number of 0.2, experimental data of the ADP inlet model indicated that the flow on the cowl windward lip remained attached at an angle of attack of 25 cleg, became unstable at 29 deg, and separated at 30 deg. An experimental through-flow test study (without propeller) using another, but similar, inlet indicated that the separation occurred at an angle of attack a few degrees below the value observed when the inlet was tested with the propeller. This evidence showed that the propeller exerted a favorable effect on the inlet low speed and high angle-of-attack performance. A stationary blockage device was designed and tested with this latter inlet to simulate the propeller effect. The test data showed that the blockage device helped prevent the inlet flow from being separated at angle of attack a few degrees higher than the inlet through-flow, but was 1 deg lower than the inlet with the propeller. In the present numerical study, this flow blockage was modeled via a PARC3D computational boundary condition (BC) called the screen BC. The principle formulation of this BC was based on the one-and-half dimensions actuator disk theory. This screen BC was prescribed at the inlet propeller face station. Numerical results were obtained for inlet flow calculations with and without the screen BC. The results with the screen BC compared better with the ADP experimental test data than those obtained without the screen BC, particularly when the inlet flow separated.

Low Aspect Ratio Transonic Rotors: Part 2—Influence of Location of Maximum Thickness on Transonic Compressor Performance

Transonic compressor rotor performance is sensitive to variations in several known design parameters. One such parameter is the chordwise location of maximum thickness. This article reports on the design and experimental evaluation of two versions of a low aspect ratio transonic rotor that had the location of the tip blade section maximum thickness moved forward in two increments from the nominal 70 percent to 55 and 40 percent chord length, respectively. The original hub characteristics were preserved and the maximum thickness location was adjusted proportionately along the span. Although designed to satisfy identical design speed requirements, the experimental results reveal significant variation in the performance of the rotors. At design speed, the rotor with its maximum thickness located at 55 percent chord length attains the highest peak efficiency among the three rotors but has lowest flow rollback relative to the other two versions. To focus on current ruggedization issues for transonic blading (e.g., bird and ice ingestion), detailed comparison of test data and analysis to characterize the aerodynamic flow details responsible for the measured performance differences were confined to the two rotors with the most forward location of maximum thickness. A three-dimensional viscous flow analysis was used to identify the performance-enhancing features of the higher efficiency rotor and to provide guidance in the interpretation of the experimental measurements. The computational results of the viscous analysis show that the difference in performance between the two rotors can be attributed to the higher shock losses that result from the increased leading edge “wedge angle” as the maximum thickness is moved closer to the leading edge. The test data and the three-dimensional viscous analysis also reveal that the higher efficiency rotor achieves the same static pressure rise potential and loading at a higher flow level than its less efficient counterpart and this is responsible for its resulting lower flow rollback and apparent loss in stall margin. Comparison of the peak efficiencies attained by the two rotors described in this article with the baseline ruggedized rotor performance presented in part 1 of this paper suggests the existence of an optimum maximum thickness location at 55 to 60 percent chord length for such low aspect ratio transonic rotors.

Three-Dimensional Flow Phenomena in a Transonic, High-Throughflow, Axial-Flow Compressor Stage

A detailed aerodynamic study of a transonic, high-throughflow, single-stage compressor is presented. The compressor stage was comprised of a low-aspect-ratio rotor combined alternately with two different stator designs. Both experimental and numerical studies are conducted to understand the details of the complex flow field present in this stage. Aerodynamic measurements using high-frequency, Kulite pressure transducers and conventional probes are compared with results from a three-dimensional viscous flow analysis. A steady multiple blade row approach is used in the numerical technique to examine the detailed flow structure inside the rotor and the stator passages. The comparisons indicate that many flow field features are correctly captured by viscous flow analysis, and therefore unmeasured phenomena can be studied with some level of confidence.

Three-Dimensional Viscous Flow Analysis of Compressor Cascade Channels.

With the rapid progress of technology in supercomputers and numerical analysis, it became possible to apply these technologies to complex flow phenomena in turbomachinery not only for research but also as design tools in industries. To catch up with this trend, we have developed a 3-dimensional NS (Navier-Stokes) numerical analysis cord for turbomachinery based on the outer flow cord for aircrafts (the Reynolds averaged Navier-Stokes equations are solved using an implicit finite-volume TVD upwind scheme with a 2-equation turbulence model). Verification by experiment is indispensable for all numerical cords, but there are not sufficient reliable experimental data, especially for the 3-dimensional case. So, we first conducted 2-dimensional compressor cascade tests with solid side walls, measured their 3-dimensional flow patterns, then compared 3-dimensional viscous flow analysis with the test data. The computed results show good agreement with experimental data, such as blade surface static pressure distribution, total pressure loss distribution at outlet of cascade, and pitchwise-averaged exit flow angle distribution under design conditions. As for higher inlet Mach number conditions, computed results show good agreement with experimental data qualitatively, but a slight quantitative discrepancy remains.

Three-dimensional Navier-Stokes simulation of Space Shuttle Main Propulsion 17-inch disconnect valves

A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle external tank/orbiter propellant feed line disconnect flapper valves with upstream elbows. The Navier-Stokes code, INS3D, is modified to handle interior obstacles and a simple turbulence model. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 million. The predicted hydrodynamical stability of the flappers correlates well with the measurements.

Navier-Stokes Flow Analysis for Hydraulic Turbine Draft Tubes

Three-dimensional turbulent viscous flow analyses for hydraulic turbine elbow draft tubes are performed by solving Reynolds averaged Navier-Stokes equations closed with a two-equation turbulence model. The predicted pressure recovery factor and flow behavior in the draft tube with a wide range of swirling flows at the inlet agree well with experimental data. During the validation of the Navier-Stokes flow analysis, particular attention was paid to the effect of grid size on the accuracy of the numerical result and the importance of accurately specifying the inlet flow condition.

Viscous Flow Analysis as a Design Tool for Hydraulic Turbine Components

Viscous flow analysis based on the full Reynolds-averaged Navier-Stokes equations is being applied to successfully predict turbulent flow characteristics and energy losses in different hydraulic turbine components. It allows the designer to evaluate the hydraulic performance of alternative designs before proceeding with laboratory testing or to perform elaborate parametric study to optimize the hydraulic design. In this paper, the applications of three-dimensional viscous flow analysis as an analytical design tool for elbow draft tube and spiral casing are presented and their impact on engineering design assessed.