Flow Field Non-uniformities Research Articles

FLUID CHARACTERISTICS AND POLISHING EXPERIMENT OF INCLINED HOLE ARRAY USING ABRASIVE WATER FLOW

Inclined hole arrays on superalloys have important applications in aeroengines. However, defects occur during fabrication of inclined holes using thermal drilling methods, i.e. electrical discharge drilling (EDD), including a recast layer and microcracks on the hole wall. Therefore, abrasive water flow polishing (AWFP) of a superalloy inclined hole array machined via EDD was investigated in this study. Two types of specimens were designed: a hole array of identical size and a hole array with an identical inclination angle. The fluid simulation revealed that the fluid velocity and pressure on the lower edge of the inclined hole were significantly higher than those on the upper edge when the fluid flowed forward. The fluid characteristics exhibited opposite trends when backward flow was implemented. Time-division bidirectional flow can effectively compensate for flow field nonuniformity and improve material removal consistency during polishing. The experimental results show that for inclined holes with identical inclination angles, the size expansion decreases with an increase in the hole diameter owing to the lower fluid velocity and material removal volume in the relatively larger holes. Consequently, surface roughness Ra increases with hole size. For inclined holes with identical diameters, the size expansions of the entrance and exit approach the same level; whereas, Ra decreased with an increase in the inclination angle. The hole taper slightly reduced in all cases. Using garnet abrasives with 1300 mesh size, 1.5 wt.% abrasive concentration, and 3 MPa fluid pressure, the surface roughness Ra of target holes was reduced from pre-polishing [Formula: see text] 5.0 [Formula: see text]m to approximately post-polishing 1.0 [Formula: see text]m. The recast layer on the hole wall caused by EDD was completely removed.

Influence of Supersonic Nozzle Design Parameters on the Unsteady Stator–Rotor Interaction in Radial-Inflow Turbines for Organic Rankine Cycles

Abstract The use of radial-inflow turbine (RIT) for organic Rankine cycle (ORC) plant sizes below 100 kW is promising, although the application remains challenging. In fact, the single-stage arrangement imposed by economic constraints and hence the large expansion ratio, together with the large molecular weight, which characterizes organic fluids, usually result in highly supersonic flows, so making the use of transonic stators often mandatory. Particularly, the influence of RIT stator design parameters on losses and the level of unsteadiness seen by the subsequent rotor is still scarcely addressed in published literature. The present work investigates the effect of the convergent–divergent stators design parameters and the resulting downstream flow field non-uniformity on the unsteady stator–rotor interaction and loss generation in ORC RIT. To this end, two stator and rotor configurations which differ by the stator design parameters (i.e., discharge metal angle and number of vanes) have been tested by means of three-dimensional (3D) unsteady CFD calculations accounting for real-gas properties. The results show that larger stator–rotor interaction is present for the case featuring higher vane count and lower outlet metal, which also features the largest fluctuations of power output and pressure force on blade, together with a substantially lower average total-to-static efficiency, as a result of a larger stator downstream pitchwise non-uniformity. Ultimately, the results indicate that only aiming for optimal stator efficiency during the stator design phase might lead to highly suboptimal configurations from the whole turbine stage point of view.

Estimation of Uncertainties for a Model Validation Experiment in a Wind Tunnel

A high-quality model validation experiment was performed in the NASA Langley Research Center Unitary Plan Wind Tunnel to assess the predictive accuracy of computational-fluid-dynamics models for a blunt-body supersonic retropropulsion configuration at freestream Mach numbers from 2.4 to 4.6. Static and fluctuating surface pressure data were acquired on a 5-in.-diam (127-mm-diam) test article with a forebody composed of a spherically blunted, 70 deg half-angle cone and a cylindrical aft body. One unpowered configuration with a smooth outer mold line was tested as well as three powered, forward-firing nozzle configurations: a centerline nozzle, three nozzles equally spaced around the forebody, and a combination with all four nozzles. A key objective of the experiment was the determination of experimental uncertainties from a range of sources such as random measurement variation, flowfield nonuniformity, and model/instrumentation uncertainties. This paper discusses 1) the design of the experiment to best capture these uncertainties for the baseline unpowered configuration, 2) the methodology used in quantifying the various sources of uncertainty, and 3) examples of the uncertainties applied to unpowered and powered experimental results. The uncertainty analysis, which concentrates on the unpowered configuration, showed that flowfield nonuniformity was the dominant contributor to the overall uncertainty. This finding is in agreement with other wind-tunnel experiments that have quantified various sources of uncertainty.

EFFECT OF THE FLOW FIELD DEFORMATION IN THE WIND TUNNEL ON THE AERODYNAMIC COEFFICIENTS

The flow field quality has a principal signification at wind tunnel measurement. The creation of the flow field of air by fan leads to the rotation of entire flow field which is, moreover, deformed at the bends of the wind tunnel with close circulation. Despite the wind tunnels are equipped with the devices which eliminate these non-uniformities, in the most of cases, the air flow field has not ideal parameters in the test section. For the evaluation of the measured results of the model in the wind tunnel, the character of flow field deformation is necessary. The following text describes the possible general forms of the flow field nonuniformity and their effect on the aerodynamic coefficients calculation.

Submerged culture process for biomass and exopolysaccharide production by Antarctic yeast: some engineering considerations

Production of biomass and extracellular polysaccharide (EPS) from psychrophilic Sporobolomyces salmonicolor AL1 in a stirred bioreactor was studied. The aspects of production technical-scale parameters, namely, bioreactor flow field, biomass and EPS production rates, oxygen mass transfer per input power, as well as important product properties, such as rheology and stability of EPS mixtures, were considered. The bioprocess was found to proceed in non-Newtonian flow with consistency coefficient rising typically to 0.03Pa.s(n) and flow index declining to 0.7. Flow modeling was carried out and showed good homogenization for substrate delivery at agitation rates exceeding 400rpm. Agitation rates lower than 400rpm were considered counterproductive due to flow field non-uniformity. The cell density reached 5g/l and EPS production yield reached 5.5g/l at production rate 0.057g EPS/l per hour (0.01g EPS/g biomass per hour). Oxygen uptake rate and oxygen transfer rate were in the range of 0.5-1.7 mmolO2/l per hour and 2-4.7 mmolO2/l per hour, respectively. The mass transfer coefficient at reaction conditions was found to be in the range [Formula: see text]. The bioprocess biological performance was higher at moderate agitation speed and revealed biomass diminution and cell inactivation by increasing impeller revolutions and shear rate. The product EPS was found to introduce shear-thinning behavior in water solutions with apparent viscosity of up to 30mPa.s and to stabilize 1-2% oil-in-water emulsions improving their lipophilic properties. The emulsion dispersion index was found to be comparable with the one of Arlacel 165, the emulsifier used in cosmetic. The long-term performance of the complex cream mixtures of the glucomannan prepared in commercial format was found promising for further application.

Modelling of flow distribution during catalytic converter light-off

The flow field non-uniformities at the inlet of catalytic converters are considered undesirable for their performance. Computational fluid dynamics (CFD) is a powerful tool for calculating the flow field inside the catalytic converter and optimising design concepts. However, the applicability of CFD for transient simulations is limited by the high CPU demands of this technique. The present study proposes an alternative computational method for the prediction of transient flow fields in axi-symmetric converters time-efficiently. The proposed flow resistance modelling (FRM) method is validated against the results of CFD predictions during a typical warm-up case. The FRM methodology is coupled with an already available transient model for heat transfer and chemical reactions in the catalyst. The effect of flow distribution on pollutant conversion and pressure drop is examined under warm-up and steady state operation.

Generation of Supersonic Swirling Flow Using Asymmetric Nozzles(3rd Report, Flow Field Evaluation by Numerical Analysis).

To improve the performance of disk MHD generators, it is suggested to install inlet swirl vanes to introduce azimuthal velocity component in the supersonic inert working gas flow at the inlet of the generator channel. But, currently used swirl vanes employing symmetric nozzles has a problem that flow field non-uniformity in azimuthal direction grows due to incompleteness of the nozzle design. For solving this problem, some swirl vane design methods using asymmetric nozzles are proposed. Technical validity of these design methods from the viewpoint of flow field uniformity is evaluated by numerical simulation of two dimensional turbulent flow. Finally, design optimization of the nozzles is discussed for introduction to disk MHD generator.

Supersonic, Inviscid, Conical Corner Flowfields

A computational procedure has been developed to predict the inviscid supersonic/hypersonic flowfield of conical internal corners. The prediction of internal corner flowfields can be important in the design of supersonic box-type inlets. The computational procedure utilizes a second-order finite-difference marching technique to approach the conical corner flow solution of Euler's equations asymptotically. These flowfields are dominated by complex shock interactions. All discontinuities, shocks, and slip surfaces are fitted with the appropriate jump conditions. The triple points (the interaction of three shocks and a slip surface) are also computed exactly. Computed results are compared with experimental data and the computational results of other investigators. In addition, the sensitivity of these flowfields to a number of geometric parameters is studied, and the impact of these flows on inlet performance is assessed. N the development of supersonic and hypersonic engine inlets, a detailed prediction of the internal flowfield is critical. Inlet designers are concerned mainly with total pressure losses, flowfield nonuniformities, and flow angularities at the compressor face or flame holders (in the case of ram/scramjets ). These conditions require a detailed description of the shock wave structure in three-dimensi onal internal flows. This paper deals with the prediction of the inviscid, supersonic flow in two-dimension al or box-type inlets, as shown in Fig. 1. In particular, this paper discusses the flowfields which are generated at the four corners of this inlet (Fig. 1, station 2). The corner flowfields generate large variations in all flowfield parameters (particularly in total pressure). In the case of ram/scramjets, these corner flows are carried to the combustion chamber where they can cause nonuniform combustion, while in the case of external compression inlets (typical of Mach 2 vehicles), a normal shock will be located before the inlet lower lip so that the corner flows will interact with this shock. Here, again, the nonuniformities in total pressure generated at the inlet corners will be preserved and eventually affect the combustion. The corner flowfields are conical if the two intersecting walls remain planar. In this situation, all flowfield variables (pressure, velocities, and entropy) are independent of the spherical radial coordinate centered at the origin of the corner flow (Fig. 1) rendering these flowfields dependent only on two space dimensions. Any fully three-dimensional computation will require conical corner flow solutions as initial conditions. In addition, the knowledge gained in a study of the conical flow problem is essential to the success of three-dimensi onal computations. This paper deals with conical corner flowfields of the type generated by two compressing wedges, since this configuration is typical of supersonic inlet flows. Two possible shock configurations could be generated by the intersection of two compressive wedges. One is called a regular reflection configuration, the other a Mach disk configuration. These terms refer to the shock conditions at the