Rectangular Vane Research Articles

Control of a Mach reflection-induced interaction using an array of vane-type vortex generators

An experimental investigation was conducted to control a Mach reflection (MR)-induced flow separation in a Mach 2.05 flow using a 18 $$^{\circ }$$ shock generator (SG). The study was extended to four SG exit heights (g / w) of 0.87, 0.81, 0.725, and 0.66 primarily to study its effect on the extent of flow separation as well as on Mach stem height, with and without control. Two vane-type vortex generator configurations, namely the ramp vane (RV) with device heights $$h/\delta = 0.3, 0.5, 0.8$$ , and 1.0 and the rectangular vane (RRV) with $$h/\delta = 0.3$$ and 0.5, were studied for control. Each control device array was implemented 10 $$\delta $$ upstream of the separation location for no control. For stable MR interactions (i.e., $$g/w = 0.87, 0.81$$ ), the extent of separation and the reattachment shock strength are seen to decrease with increase in RV height (with $$h/\delta =1.0$$ device showing 17% reduction). However, for unstable MR condition (i.e., $$g/w = 0.725$$ ), RV devices of $$h/\delta = 0.8$$ and 1.0 become ineffective. The RRV2 device ( $$h/\delta =0.5$$ ), on the other hand, was found to be more effective in reducing the extent of separation in both the stable (31%) and unstable (24%) MR conditions. The effectiveness of each control device is also accompanied with an increase in height of the Mach stem. This is, however, not seen as a serious limitation since in such strong interactions it is more important to prevent or avert an intake unstart condition. The separation shock unsteadiness or the $$\sigma _{\mathrm{max}}/P_{\mathrm{w}}$$ value, on the other hand, is seen to increase considerably with controls and seems to be almost independent for $$h/\delta \ge 0.5$$ .

Mixed Acoustic-Entropy Combustion Instabilities in a Model Aeronautical Combustor: Large Eddy Simulation and Reduced Order Modeling

This article focuses on combustion instabilities (CI) driven by entropy fluctuations which is of great importance in practical devices. A simplified geometry is introduced. It keeps the essential features of an aeronautical combustion chamber (swirler, dilution holes, and outlet nozzle), while it is simplified sufficiently to ease the analysis (rectangular vane, one row of holes of the same diameter, no diffuser at the inlet of the chamber, and circular nozzle at the outlet). A large eddy simulation (LES) is carried out on this geometry and the limit cycle of a strong CI involving the convection of an entropy spot is obtained. The behavior of the instability is analyzed using phenomenological description and classical signal analysis. One shows that the system can be better described by considering two reacting zones: a rich mainly premixed flame is located downstream of the swirler and an overall lean diffusion flame is stabilized next to the dilution holes. In a second step, dynamic mode decomposition (DMD) is used to visualize, analyze, and model the complex phasing between different processes affecting the reacting zones. Using these data, a zero-dimensional (0D) modeling of the premixed flame and of the diffusion flame is proposed. These models provide an extended understanding of the combustion process in an aeronautical combustor and could be used or adapted to address mixed acoustic-entropy CI in an acoustic code.

Numerical Investigation of Back Vane Design and Its Impact on Pump Performance

Adding back vanes to the rear shroud of centrifugal pumps is sometimes practiced in order to alleviate large axial forces. Effective design and flow characteristics of back vanes remain obscure due to lack of knowledge associated with experimental complexities in study of this area. In this study, various design parameters of the conventional noncurved rectangular back vanes are evaluated using computational fluid dynamics (CFD). Furthermore, the complex flow structure at the rear chamber of these pumps is illustrated and discussed with the advantage of CFD which is a highly costly and taxing job if one chooses to capture it using experimental methods. Effect of back vanes outer radius, width, clearance, thickness, vane angle, and number of vanes on pump characteristics and axial thrust has been investigated. New findings of this study show that back vanes are capable of canceling the axial thrust in a large range of flow rates without a penalty to the machine efficiency, provided that suitable design parameters are selected. In addition, the best efficiency point (BEP) will not be affected by usage of back vanes. The rear chamber’s flow pattern suggest that back vanes have a repumping effect causing increased pump head at longer back vane configurations.

Shearing Failure Visualization via Particle Tracking in Soft Clay Using a Transparent Soil

In situ undrained shear strength measurement devices such as the vane shear test, cone penetrometer, and full-flow penetrometers (e.g., T-bar and ball) have been increasingly used as a part of geotechnical site investigations for soft clay deposits. Previous attempts to visualize the shear failure surfaces on these devices included either significant disturbance of the soil sample (permeated with resin and thin-sectioning) or involved methods of shearing along a transparent surface creating boundary effects. This paper described the use of non-invasive testing procedures to determine the failure surface of several in situ shear strength measurement devices in a soft clay surrogate (LAPONITE RD, a trademark of BYK Additives and Instruments). A series of tests were performed using two sizes of rectangular miniature vanes, two types of full flow penetrometer tests (T-bar and ball), and a cone penetrometer in LAPONITE RD samples. Laser planes were used to illuminate particles in the transparent material during shearing. Particle tracking techniques were used to visualize the failure surfaces and flow mechanisms for each device. Experimental results were compared with theoretical and numerical simulations of the failure surfaces and flow characteristics by previous researchers. The present work contributed to the understanding of undrained shear strength testing devices by an in situ assessment of the evolution, geometry, and structure of the failure surfaces and full-flow mechanisms.

Numerical simulation of turbulent flow affected by vortex generators in straight channel

The presented work is the next step after several experimental examinations of the vortex generator (VG) influence on flow separation occurring on a model of the NACA 63A421 airfoil with a deflected simple flap. The other purpose of this simulation is to obtain beneficial information that can be utilized for the preparation of the experimental investigation of the same configuration using Particle image Velocimetry method (PIV) in the future. The numerical simulation was performed for one single pair and two pairs of low-profile VGs of the same size, whose heights were smaller than the boundary layer thickness. The rectangular vane type VGs in such configuration, which generates counter-rotating vortices, was examined. The behaviour of vortices produced by VG pair or pairs in several positions downstream the VGs is investigated and will be used as a background of the measurement.

Enhancing Utility of Submerged Vanes with Collar

Submerged vanes are submerged foils of low height and larger length, constructed in a river at an angle of attack α to the flow to modify the near-bed flow pattern and redistribute flow and sediment transport within the channel cross section. At a Froude number (F) of 0.13, the local scour development around the submerged vane without a collar was not enough to dislodge the vane whereas at F=0.25, there was a significant local scour hole around the vane and the vane was dislodged. With the introduction of a collar at the leading edge of a submerged vane, the scour depth at the leading edge of the vane was reduced to zero. A collar of circular shape was found more suitable for a rectangular vane. Recommendations for sizing collars at two values of F are given. The optimal α for a rectangular vane with a collar was found close to 40°. The study clearly indicates the advantages of using collars in case of submerged vanes and provides insight into selection of appropriate collar shapes.

Computational Investigation of a Race Car Wing With Vortex Generators in Ground Effect

Vortex generators can be applied to control separation in flows with adverse pressure gradients, such as wings. In this paper, a study using three-dimensional steady computations for an inverted wing with vortex generators in ground effect is described. The main aim is to provide understanding of the flow physics of the vortex generators, and how they affect the overall aerodynamic performance of the wing to complement previous experimental studies of the same configuration. Rectangular vane type sub-boundary layer and large-scale vortex generators are attached to the suction surface of the wing, including both counter-rotating and co-rotating configurations. In order to provide confidence, Reynolds-averaged Navier–Stokes simulations using the Spalart–Allmaras turbulence model are validated against the experimental results regarding force, pressure, and wake characteristics, with the validation exhibiting close agreement with the experimental results. The streamwise friction shows the downwash induced by the generated vortex acts to suppress flow separation. The flow field survey downstream of the vortex generators features breakdown and dominance of the generated vortex in the flow. The vortex generated by the counter-rotating sub-boundary layer vortex generator grows in size and breaks down as it develops downstream, while the vortex generated by the counter-rotating large-scale vortex generator shows high vorticity even further downstream, indicating the persistence of the vortex in the flow. The flow field behind the co-rotating sub-boundary layer vortex generator is dominated by a lateral flow, having the spanwise flow component rather than a swirling flow, and the vortex quickly dissipating as it develops downstream. The results from this paper complement previous experimental measurements by highlighting the flow physics of how vortex generators can help control flow separation for an inverted wing in ground effect, and how critical vortex generator type and size are for its effectiveness.

Flow Physics of a Race Car Wing With Vortex Generators in Ground Effect

This paper experimentally investigates the use of vortex generators for separation control on an inverted wing in ground effect using off-surface flow measurements and surface flow visualization. A typical racing car wing geometry is tested in a rolling road wind tunnel over a wide range of incidences and ride heights. Rectangular vane type of sub-boundary layer and large-scale vortex generators are attached to the suction surface, comprising counter-rotating and corotating configurations. The effects of both device height and spacing are examined. The counter-rotating sub-boundary layer vortex generators and counter-rotating large-scale vortex generators suppress the flow separation at the center of each device pair, while the counter-rotating large-scale vortex generators induce horseshoe vortices between each device where the flow is separated. The corotating sub-boundary layer vortex generators tested here show little evidence of separation control. Increasing the spacing of the counter-rotating sublayer vortex generator induces significant horseshoe vortices, comparable to those seen in the counter-rotating large-scale vortex generator case. Wake surveys show significant spanwise variance behind the wing equipped with the counter-rotating large-scale vortex generators, while the counter-rotating sub-boundary layer vortex generator configuration shows a relatively small variance in the spanwise direction. The flow characteristics revealed here suggest that counter-rotating sub-boundary layer vortex generators can provide effective separation control for race car wings in ground effect.

VORTICITY WITH DIFFERENT SHAPES OF SUBMERGED VANES

ABSTRACT At optimal angle of attack, vanes have the maximum strength of secondary circulation. For the same hydraulic condition, the maximum strength of vane induced secondary circulation also depends on their shapes. Optimal angle of attack in case of rectangular submerged vane with collar is very close to 40° where as in case of double curve vane type I, double curve vane type II, J1 type and J2 type vane is very close to 45°. Strength of vane induced secondary circulation in terms of moment of momentum depends upon various parameters. A dimensional analysis approach has been attempted to get dimensionless moment of momentum. The maximum strength of vane induced secondary circulation in terms of dimensionless moment of momentum is greater in case of rectangular vane than that in case of curved vanes in the same flow conditions and same height and length of vanes.

A Study of Undrained Shear Strength Using Various Vanes

Abstract A field study of the undrained shear strength of a sensitive clay deposit was carried out by means of various vane configurations. Rectangular, rhomboidal, triangular, and elliptic vane blades were used. The assumption of isotropy of the undrained shear strength indicates that a uniform shear stress distribution gives a better fit to the observed response than a triangular distribution

Measurements of shear stress distribution on the edges of a shear vane blade

The primary measurement carried out is that of torque. Soil strength is derived from this torque. The effects of the anisotropy and progressive failure, although they have been investigated, are largely ignored. This note discusses the distribution of shear stress measured by laboratory tests in Leighton Buzzard sand and field tests in over-consolidated, saturated, brown London clay. A rectangular vane 120 mm wide and 240 mm long was made so that foil strain gauges could be used to measure the loads on various parts of the vane blades. Equivalent shear stress distributions are plotted for various angular rotations of the vane shaft together with least squares regression curves fitted to normalised versions of the data. Normalised distributions from the vertical blade edge had weak correlations due to the scatter arising from the layers in the soils. However the distributions from the horizontal blade edge had much stronger correlations as the stresses were mobilised in a uniform horizontal layer of soil. It was found that shear force measurements gave values within 10 per cent of the torques measured at the top of the shear vane shaft indicating that most of the shearing resistance arises at the blade edges. Little torque arises from soil distortion in the sectors between adjacent blades. This concentration of shear distortion at the blade edges was confirmed radiographically. (TRRL)

Vane cone test of snow

To predict vehicle mobility or drawbar pull of a tracked oversnow vehicle on snow covered terrain, the fundamental relations between shear strength, normal stress and deformation were studied experimentally for several types of fresh snow and sintered snow. For this purpose, vane cone (apex angle 30°, height 36.5 mm and 69.9 mm) penetration tests at high penetration rate (3.7 mm/sec) and vane cone shear tests at high shear rate (1.89 mm/sec and 3.49 mm/sec) have been performed in a cold room at constant temperrature -13°C±1°C. Load and torque have been measured automatically for penetration and rotation tests of the vane cones.The results show that the shear deformation properties show some rigid plastic behavior and the relation between shear stress τ and deformation X is given as follows τ = τ0 exp (-2X). And as all vane cone shear tests on snow were test under a normally compressed state, the relation between shear stress τ and normal stress σ satisfied the Coulomb failure criteria as follows τ = C+ σtan ψ (C; cohesive strength, ψ; angle of internal friction). And maximum cone index and vane cone shear strength depend not only on density but also degree of sintering and grain-size distribution of snow particles.The most suitable in-situ test method to predict the drawbar pull property of a tracked oversnow vehicle seems to be to perfom both rectangular plate loading test and vane cone tests simultaneously.

A generalized correction factor for the Knudsen radiometer gauge with arbitrary vane and heater shape

A general expression involving the transverse radiometer effect for the response of a Knudsen gauge, valid for any vane and heater shape, is derived. In principle, the formula is also valid for all distances and dimensions. The calculation in the case of circular discs is presented in detail and the results for spherical and rectangular vanes and heaters are discussed. A simple configuration representing a very good approximation to Knudsen's original formula is proposed.

Vibrating Vane, Absolute Gas Pressure Gauge

An oscillating rectangular vane suspended by a fine quartz fiber is used to determine the absolute pressure of the gas in which it is located. Aside from being an absolute instrument, the advantages of such a device are (1) simplicity, (2) the fact that it does not change the pressure when an observation is made as do many other types of gauges, and (3) the absence of a heated filament which may decompose the gas under study.

Knudsen gauges

A brief review of the development and applications of the Knudsen gauge is followed by a detailed description of improved forms of metal and glass gauges. Their performance with respect to factors such as outgassing, methods of suspension, extension of range by electromagnetic compensation, and damping are discussed. The theory of the absolute manometer is reviewed. In particular, the fundamental assumptions concerning accommodation coefficient, the edge effect due to large heater-to-vane distance, and vane temperature, in the low pressure (Knudsen) region are discussed. A theory is developed to give a correction factor for a rectangular vane and heater valid for any dimensions and distance. It is shown that under certain conditions calibration is independent of the temperature of the vane.