Vane Configuration Research Articles

Aerodynamics of a Letterbox Trailing Edge: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution

A letterbox trailing edge configuration is formed by adding flow partitions to a gill slot or pressure side cutback. Letterbox partitions are a common trailing edge configuration for vanes and blades, and the aerodynamics of these configurations are consequently of interest. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a vane with letterbox partitions in a large-scale low speed cascade facility. These measurements are compared with exit surveys of both the base (solid) and gill slot vane configurations. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flow). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at a measuring station representing an axial chord spacing of 0.25 from the vane trailing edge plane. Differences between losses with the base vane, gill slot vane, and letterbox vane for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses, and losses due to the separation off the exit slot lip and partitions. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions at the different Reynolds numbers. The letterbox configuration has been found to have slightly reduced losses at a given flow rate compared with the gill slot. However, the letterbox requires an increased pressure drop for the same ejection flow. The present paper together with a related paper (2008, “Letterbox Trailing Edge Heat Transfer—Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness,” ASME, Paper No. GT2008-50474), which documents letterbox heat transfer, is intended to provide designers with aerodynamic loss and heat transfer information needed for design evaluation and comparison with competing trailing edge designs.

Hybrid Reynolds-Average Navier-Stokes and Kinetic Eddy Simulation of External and Internal Flows

thus alleviating the grid-spacing dependency found in other detached eddy simulation and hybrid Reynoldsaveraged Navier–Stokes and large eddy simulation models. Within the hybrid Reynolds-averaged Navier–Stokes andkinetic eddy simulation model, fourdifferent options (a combination of two different blending functions andthe use of realizability constraints to bound the kinetic eddy simulation model parameters) have been evaluated and studied for flows over airfoils (RAE2822, NACA0015) and a turbine vane configuration. Although all four options showed good correlation with the test data, blendingk-!-SST with kinetic eddy simulation using Menter’sk-!-SST F2 function showed better predictions in separated flows than using the baseline k-!-SST model. OST current computational fluid dynamics (CFD) methods used in the simulation and analysis of external and internal flows are based on Reynolds-averaged Navier–Stokes (RANS) approaches, which depend on turbulence-closure models to provide flowfield turbulent variables. Although RANS approaches yield good predictions for attached flowfields, they fail to accurately predict flow structures in separated-flow regions because they resolve only a portion of the turbulence scales of interest. Of course, the ideal approach would be direct numerical simulation (DNS), because the entire range of spatial and temporal scales of turbulence is resolved, but the computational cost of DNS is prohibitive. Another intermediate technique between DNS and RANS has been proposedtoreplaceRANSinsuchcases;thisapproachiscalledlarge eddy simulation (LES). In LES, the contribution of large energy-containing structures and all scales larger than the grid resolution to momentum and energy transfer is computed, and the effect of subgrid unresolved small

The flow rectification of a vaned microdiffuser: A numerical investigation

This paper presents a numerical investigation to characterize the flow rectification of a dynamic vaned microdiffuser pump. To study the impacts of vane configuration in microscale, two vanes stretching from the inlet region to the outlet region are added to divide the microdiffuser into three flowing passages. By imposing a sinusoidal pressure at the inlet, two geometric parameters are considered: half angle of the diverging section θ and half angle between adjacent vanes F. We find that when the angle between adjacent vanes remains the same (fixed F), net flow rate is augmented with increasing θ. In contrast, there exists an optimized vane configuration while the diverging section is unchanged (fixed θ). For F < θ/3, increase in F helps to improve flow rectification. For F > θ/3, further increase of F results in narrower side passages, and net flow rate diminishes consequently. Hence, best flow rectification is achieved when the diverging section is equally divided by the vanes, i.e. F = θ/3. The influences of vane configuration in flow rectification can be categorized into three regimes: central passage dominated, best rectification, and side passage dominated.

Analysis of the effect of mixing vane geometry on the flow in an annular centrifugal contactor

AbstractThe annular centrifugal contactor is a compact mixer/centrifuge developed for solvent extraction processes for recycling used nuclear fuel. This research effort couples computational fluid dynamics (CFD) modeling with a variety of experimental observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the volume‐of‐fluid method combined with large eddy simulation of turbulence was found to have very good agreement with the experimental measurements. A detailed comparative analysis of the flow and mixing with different housing vane geometries (four straight vanes, eight straight vanes, and curved vanes) was performed. Two additional variations on the eight straight vane geometry were also simulated. This analysis determined that at the simulated moderate flow rate the four straight mixing vane geometry has greater mixing and fluid residence time as compared to the other mixing vane configurations. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Stall inception process and prospects for active hub-flap control in three-stage axial flow compressor

The possibility to apply the active hub-flap control method, which is a proven rotating stall control method for a single-stage compressor, to a 3-stage axial compressor is experimentally discussed, where complex rotating stall inception processes are observed. The research compressor is a 3-stage one and could change the stagger angle settings for rotor blades and stator vanes. Sixteen rotor blade/stator vane configuration patterns were tested by changing stagger angle for the stator vanes. By measurement of surface-pressure fluctuation, stall inception processes are investigated and the measured pressure fluctuation data is used as a predictive signal for rotating stall. The experimental results show that the stall detection system applied to active hub-flap control in a single-stage compressor could be usefully applied to that in a 3-stage compressor with a more complex stall inception process.

Gill Slot Trailing Edge Aerodynamics: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution

Gill slots (also called cutbacks) are a common method to cool the trailing edge of vanes and blades and to eject spent cooling air. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a gill slot vane in a large-scale, low speed cascade facility. These measurements are compared with exit surveys of the base (solid) vane configuration. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flows). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at two stations representing axial chord spacings of 0.25 and 0.50. Differences between losses with and without the gill slot for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses and losses due to the separation off the gill slot lip. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions and at the different Reynolds numbers. The turbulence condition has been found to have only a small effect on the increase in losses due to the gill slot. However, decreasing Reynolds number has been found to produce an increasing increment in losses. The present paper, together with a companion paper (2007, “Gill Slot Trailing Edge Heat Transfer—Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness,” ASME Paper No. GT2007-27397), which documents gill slot heat transfer, is intended to provide designers with the heat transfer and aerodynamic loss information needed to compare competing trailing edge designs.

Boundary-Layer-Ingesting Inlet Flow Control

An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5% -scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass-flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally, a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass-flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.

Enhancement of heat transfer in a typical pressurized water reactor by different mixing vanes on spacer grids

The flow mixing devices on a grid spacer are designed to enhance the turbulence and heat transfer in sub-channels. The present study evaluates the effects of different mixing vane configurations on flow pattern and heat transfer in the downstream of the mixing vanes in the sub-channels of fuel assembly. This is done by obtaining velocity and pressure fields, turbulent intensity and the heat transfer coefficient using a three-dimensional CFD analysis. Two blade groups, two-dimensional and three-dimensional, were modeled. The two-dimensional blades are classified in ring type, diamond type, square type, homographic type and multiply type. Three-dimensional blades containing split vane, ripped open, trumpet shaped and split trumpet shaped are applied in a 2 × 2 rod bundle array. Also, a 3 × 3 rod bundle array is modeled to evaluate the neighborhood effects on the thermo-hydraulic parameters. The latter model shows a good comparison with the available experimental data by 5–12% difference. A standard K-epsilon model is used as a turbulence model and the symmetry condition is set as boundary conditions. It was confirmed that the turbulence in the sub-channel was significantly promoted by spacer and mixing devices. However, their effects rapidly decreased to a fully developed level after passing approximately 10 times the hydraulic diameter downstream of the spacer. The CFD results showed good agreement with the measurements. The static pressure of the fluid in the flow direction drops rapidly, then in a very short distance rise up, followed by a decrease near to the linear slope down stream. The split trumpet vane was the best with a 14% increase in the heat transfer coefficient, however regarding the manufacturing possibilities, the split vane spacers are expected to significantly enhance the overall heat transfer of a nuclear fuel assembly about 9.82% with a reasonable increase in the pumping cost.

A reduced efficiency approach-based process model for a circulating air classifier

The performance of a circulating air classifier has been studied systematically by conducting experiments over a range of process and design variables. It is found that while the overall induced flow rate is proportional to the speed of rotation of the wheel, the circulation pattern inside the classifier depends on the configuration of stationary guide vanes. This is found to have a significant effect on the range of operability of the classifier. Results show that the cut size, sharpness of separation and the bottom and top size selectivity increments are influenced strongly by the stationary guide vane configuration. Using experimental data from a dense material (fly ash) and a light material (rice husk), a model based on the reduced efficiency curve approach, originally proposed for hydrocyclones, has been developed to predict the performance of the classifier.

Integrated Methods for the Design of a Thrust Reverser Cascade

The design of a cascade box within a cold stream thrust reverser is studied with a view to establishing a methodology for the optimization of aerodynamic, structural, manufacturing, and cost parameters. Aerodynamic and structural simulations have been carried out for three different design configurations. When the weight of the original cascade design (design 1) was reduced by 5% (design 2) and then 10% (design 3) by modifying the vane configurations, it was found that although total reverse thrust was reduced by 9% for the reduced-weight designs, the structural performance of the cascade improved when compared to the original design. Cost analyses show that labor costs for the reduced-weight designs are reduced when compared to the original design, due to reduced casting times and improved component handling characteristics. Although material costs are lower for the reduced-weight designs, increased component complexity increases tooling costs. The total unit cost of cascade design 2 is 4.5% more than design 1, and the unit cost of design 3 is 0.14% higher than design 1. The increase in cost of two aircraft nacelle systems for a single aircraft using design 3 cascade boxes is $5.04. The increased expenditure on design 3 cascade boxes will be recovered in the first year of operation because the 10% weight reduction reduces operational cost by $260 over 12 months. Although only three cascade box configurations have been used, the methodologies developed will be equally applicable to further cascade designs or indeed any complex component where structural performance is a key requirement and multidisciplinary simulation is heavily used.

수면관통형 터널 프로펠러의 성능해석을 위한 실험적 연구

A surface piercing propeller (SPP) in tunnel has been proposed recently as a new propulsion system for a high speed air cavity ship. The purpose of the present study is to investigate the characteristics of the SPP in tunnel through a series of model tests. A model propulsion system is placed on a dummy body made of Acrylics. The tunnel is divided into two regions by a guide vane extending from the inlet to the center of the propeller shaft. Air has been supplied from an air nozzle placed at the bottom of the dummy body and the changes in propeller performances caused by the air flow are investigated. The measurements are done for open water and in-tunnel conditions, both for fully and partially submerged propeller. The influence of the guide vane configurations on the propeller performance is also studied. The experiments are performed at the variable pressure circulation water channel of Inha University⼊夀Ѐ敳捯℀郫蒈胬ꂈ뷬ꂄ룪뢰藭频谀

Asymmetric Flow in Symmetric Supercritical Expansions

A theory presented previously by the writer explained the asymmetric flow patterns occurring in symmetric rectangular expansions with subcritical flow. The theory is extended in the present paper to supercritical flows, in which the hydraulic jump is one of the flow features. The theory is shown to agree with available observations. Transverse oscillatory conditions are discussed in terms of a dynamic instability that can accompany static stability. The ranges for which experimental data are available with which to test the theory are identified, making it apparent where additional data would be useful for the full range of the problem. The phenomenological understanding provided by the present paper is important to the development of stabilization measures. In addition to stabilization by submergence, the hydraulic jump should be amenable to stabilization by other referenced methods, including various vane configurations and pipe communication between the eddy regions.

Aerodynamic Losses of a Cambered Turbine Vane: Influences of Surface Roughness and Freestream Turbulence Intensity

The effects of surface roughness and freestream turbulence level on the aerodynamic performance of a turbine vane are experimentally investigated. Wake profiles are measured with three different freestream turbulence intensity levels (1.1%, 5.4%, and 7.7%) at two different locations downstream of the test vane trailing edge (1 and 0.25 axial chord lengths). Chord Reynolds number based on exit flow conditions is 0.9×106. The Mach number distribution and the test vane configuration both match arrangements employed in an industrial application. Four combered vanes with different surface roughness levels are employed in this study. Effects of surface roughness on the vane pressure side on the profile losses are relatively small compared to suction side roughness. Overall effects of turbulence on local wake deficits of total pressure, Mach number, and kinetic energy are almost negligible in most parts of the wake produced by the smooth test vane, except that higher freestream losses are present at higher turbulence intensity levels. Profiles produced by test vanes with rough surfaces show apparent lower peak values in the center of the wake. Integrated aerodynamic losses and area-averaged loss coefficient YA are also presented and compared to results from other research groups.

Effects of Impeller Vane Configurations and Seed Size on Dehulling Efficiency of Sunflower Seeds Using a Centrifugal Sheller

The effect of machine parameters as well as size on dehulling performance of sunflower seeds have been studied using a centrifugal sheller Forward-curved impeller vanes made of aluminum gave highest dehulling efficiency (80.12%) than that with mild steel or rubber vanes. Large size sunflower seed (length &gt; 10 mm) at 7.3% (d.b.) showed the higher dehulling efficiency (80.47%), minimum specific energy (7.42kJ/kg) and moderate non-recoverable kernel fraction (9.82%) using forward curved aluminum vane. However, the non-recoverable kernel fraction was found to be minimum (6.21%) with the medium size seed having average length between 8.0 and 10.0mm.

Optimization Design for Thrust Reverser Cascade with a View to Reduce Noise

reverser considered in this paper uses the natural blockage concept, with only the fan duct flow being reversed. This paper focuses on the study of the aerodynamic performance of the cascade within a cold stream thrust reverser. Aerodynamic simulations are carried out using realistic operating conditions, for idealized cascade models representing three design options. The aim of this work is to investigate whether the aerodynamic performance of the thrust reverser cascade has been improved while minimizing weight of the cascade. In addition, t1his is the first attempt of us to considering noise reduction during design of the thrust reverse. The numerical simulations show that despite a reduction in total reverse thrust for the weight reduced designs, the supersonic flow regime, which existed in the original design, was eliminated after changing vane configurations made with the 5% and 10% weight reductions. The aerodynamic performance around the cascade and in the fan duct within the thrust reverser has been improved. Moreover, the acoustic characteristics of the thrust reverser are improved too. The total reverse thrust is not significantly affected with the modified cascade.

Enhancement of thrust reverser cascade performance using aerodynamic and structural integration

AbstractThis paper focuses on the design of a cascade within a cold stream thrust reverser during the early, conceptual stage of the product development process. A reliable procedure is developed for the exchange of geometric and load data between a two dimensional aerodynamic model and a three dimensional structural model. Aerodynamic and structural simulations are carried out using realistic operating conditions, for three different design configurations with a view to minimising weight for equivalent or improved aerodynamic and structural performance. For normal operational conditions the simulations show that total reverse thrust is unaffected when the performance of the deformed vanes is compared to the un-deformed case. This shows that for the conditions tested, the minimal deformation of the cascade vanes has no significant affect on aerodynamic efficiency and that there is scope for reducing the weight of the cascade. The pressure distribution through a two dimensional thrust reverser section is determined for two additional cascade vane configurations and it is shown that with a small decrease in total reverse thrust, it is possible to reduce weight and eliminate supersonic flow regimes through the nacelle section. By increasing vane sections in high pressure areas and decreasing sections in low pressure areas the structural performance of the cascade vanes in the weight reduced designs, is improved with significantly reduced levels of vane displacement and stress.

Computation of rotor wake turbulence noise

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged Navier–Stokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust spectra of acoustic power are computed and compared with the measured spectra where possible. The acoustic power levels and shape of the predicted spectra are in good agreement with the measured data for the fan exhaust duct radiation at approach condition where direct comparisons are possible. The predicted spectra show the experimentally observed trends with fan tip speed, vane count and vane sweep. The results also demonstrate the validity of using computational fluid dynamics based turbulence information for fan broadband noise calculations.

Weight reduction methodologies for a thrust reverser cascade using aerodynamic and structural integration

This paper focuses on the aerodynamic and structural design of the cascade within a cold stream thrust reverser. Methodologies are established for improving the efficiency of the design process. Aerodynamic and structural simulations are carried out using realistic operating conditions for idealized cascade models representing three design options. The aim of this work is to minimize weight while maintaining or improving aerodynamic and structural performance. Total reverse thrust decreases by 0.28 per cent when the aerodynamic performance of the deformed cascade is compared with the undeformed case. This shows that, for the conditions tested, the displacement of the cascade vanes has a minimal affect on aerodynamic performance, and that there is scope for weight reduction. When cascade weight is reduced by 5 per cent and then 10 per cent by modifying the vane configurations, the structural performance of the cascade improves, with significantly reduced levels of vane displacement. Although reverse thrust is reduced by 9 per cent for both of the reduced-weight designs, the maximum airspeed within the thrust reverser is subsonic. The maximum airspeed is above Mach 1 for the original design. This reduces the risk of the structure being subjected to the complex loading conditions associated with the shock waves due to supersonic air flow.

Engine Cycle and Exhaust Configuration for Quiet Supersonic Propulsion

The thermodynamics and acoustics of a fixed-cycle, bypass ratio 3 supersonic engine with an innovative noise suppression scheme is explored. The silencing method entails installation of variable turning vanes in the bypass exhaust of a separate-flow turbofan engine. During noise-sensitive segments of flight, the vanes impart a slight downward tilt to the bypass plume relative to the core plume, thus thickening the bypass stream on the underside of the jet. This results in a reduction of the convective Mach number of instability waves that produce intense downward sound radiation. Subscale experiments show that, relative to the mixed-flow exhaust, the coaxial separate-flow exhaust with vanes reduces the peak overall sound pressure level by 8 dB and the effective perceived noise level by 7 dB. The noise-equivalent specific thrust on takeoff is reduced from 490 to 390 m/s. Compared to a current-generation low-bypass turbofan engine, the bypass ratio 3 engine is estimated to be 13 dB quieter with the mixed-flow exhaust and 20 dB quieter with the aforementioned suppression scheme. The vane configuration of this study is estimated to cause a thrust loss of 1% at takeoff and 0.25% at supersonic cruise.

Development and performance tests of a sheanut cracker

A sheanut cracker was designed, constructed and tested to evaluate its performance. The cracker, which consists of a hopper fitted with a flow rate control device, a cracking unit, winnowing unit and power system, operates on the principle of impact using centrifugal force from a spinning disc. Results of performance tests showed that moisture content affected the performance indicators (percentage effective cracking, percentage breakage, percentage of partially cracked nuts, percentage of uncracked nuts and winnowing efficiency). Feed rate had a statistically significant effect on other indicators than the percentages of partially cracked and uncracked nuts at 5% level of significance. Disc vane configuration had no significant effect on percentage breakage and percentage of partially cracked nuts at the 5% level, but significantly affected both the percentage effective cracking and percentage of uncracked nuts at the 5% level, and winnowing efficiency at the 1% level of significance. The moisture content and feed rate that gave the highest cracker performance was found to be 22.7% (db) and 11.4 kg/h respectively. At the above conditions, the radial vane configuration, which among the three vanes employed, had maintained the best cracking performance, also gave the highest percentage effective cracking of practically 100% and about 97% winnowing efficiency. No breakage, partially cracked nuts and uncracked nuts were recorded with the radial vane configuration.