Lip Radius Research Articles

Design Analysis of Open and Ducted Propellers in UAV Application

The aim of the study was to determine the feasibility of implementing a ducted propeller system for small scale drones. 5” propeller drones are common in first person view (FPV) drone racing and cinematography, increasing the likelihood of injury due to untrained pilots, of which the majority are laceration injuries due to the propeller blades. Furthermore, the addition of a duct improves the thrust output of the entire system. A few key parameters are identified, of which were manipulated to determine the optimum values through a series of ANSYS Fluent CFD simulations. Introducing a duct is shown to reduce the lift a propeller produces; however, the reduction is offset by the lift generated by the duct. Blade tip clearance was investigated, with the optimum value found to be 0.25 mm, producing the most lift from the duct and least reduction of propeller lift, and with thrust outputs up to 35.568% more in some cases compared to open propeller. It was observed that increasing the BTC significantly reduced duct lift. Diffuser length simulations provided unconclusive results, with the duct lift varying depending on the diffuser length. However, the optimum diffuser length was determined to be 65 mm with respect to thrust outputs. In comparison, inlet lip radius shows a clear pattern, deviating from the optimum value of 16.5 mm reduces the duct lift produced, with smaller values severely decreasing performance.

Hovering efficiency optimization of the ducted propeller with weight penalty taken into account

The ducted propeller is superior to the open propeller in hovering efficiency. However, the overall system efficiency of a ducted propeller is reduced due to its heavy structure. If the weight penalty is taken into account, will the ducted propeller still be superior to an open propeller? And in this scenario, how will a ducted propeller with better efficiency than an open propeller be designed? This paper investigates these questions by parametric analysis based on experiments and then parametric optimization that involves hovering efficiency and structural weight in objective functions. Both multi-disciplinary design optimization and multi-objective programming are performed by surrogate-based optimization. An in-house automatic structured mesh generation module is developed to deal with significant geometry variation in design space. Finally, the optimization results are validated by post-optimization experiments. The results of experiment and optimization indicate that the effects of weight penalty play a leading role at low disk loading and hence in this case, the one with lighter structure is superior. But at high disk loading, as thrust gets higher, the leading factor turns into aerodynamic hovering efficiency, therefore the one with higher aerodynamic hovering efficiency prevails. The multi-objective optimization produces an L-shaped Pareto front, and the optimum of multi-disciplinary optimization is quite close to the Pareto front knee point. The designs in this region encounter limited aerodynamic hovering efficiency loss but gain significant weight reduction. Therefore, we can obtain a ducted propeller superior to an open propeller in system efficiency with pretty low disk loading, although the weight penalty is considered. These designs feature a relatively large inner lip radius, a small outer lip radius, and a short or even no diffuser. This means that the inner lip radius contributes the most to the aerodynamic hovering efficiency, followed by the diffuser and outer lip. These designs have very low height to diameter ratio therefore they can be easily integrated into aircraft structure.

Adaptive-surrogate-based robust optimization of transonic natural laminar flow nacelle

Natural Laminar Flow (NLF) technology is very effective for reducing the skin friction drag of aircraft engine nacelle, but the aerodynamic performance of NLF nacelle is highly sensitive to uncertain working conditions. Therefore, it’s imperative to incorporate uncertainties into the design of NLF nacelle. In this study, for a robust optimization of NLF nacelle and for improving its efficiency, an adaptive-surrogate-based robust optimization strategy is established, which is an iterative optimization process where the surrogate model is updated to obtain the real Pareto front of multi-objective optimization problem. A case study is carried out to validate its feasibility and effectiveness. The results show that the optimization increases the favorable pressure gradient region and the volume ratio of the nacelle by increasing its lip radius and reducing its maximum diameter. And the aerodynamic robustness of the NLF nacelle is mainly determined by the lip radius, maximum diameter of nacelle and location of the maximum diameter. Compared to the initial nacelle, the optimized nacelle maintains a wide range of low drag and high laminar flow ratio in the disturbance space, which extends the average laminar flow region to 21.6% and facilitates a decrease of 1.98 counts in the average drag coefficient.

CFD Study of a New Annular Lift Fan Configuration with High Lift Efficiency

A new annular lift fan configuration that has very high lift efficiency is explored by using a numerical scheme. The inlet lip radius and diffuser angle are maximized by semicircle duct walls and the location of the lift fan is moved from the throat to the diffuser area to maximize the diffusion effect of the ducted fan. The improved lift fan achieves the figure of merit of 0.772 and the power loading of 9.03 lbs/hp without ground effect, very close to the theoretical limit. Under the ground effect, the figure of merit reaches 0.822 with the power loading of 9.62 lbs/hp. The improved lift efficiency deteriorates the transition characteristics with higher momentum drag and pitching moment. However, with the aid of jet thrusts directly providing part of the lift during transition, the peak of momentum drag and pitching moment can be lowered. A total thrust to weight ratio of 0.7 is enough for all of the requirements in transition and in hover and for the maximum speed of 0.75 Mach in cruise flight.

A hybrid CFD/characteristics method for fast characterization of hypersonic blunt forebody/inlet flow

A hybrid CFD/characteristic method (CCM) was proposed for fast design and evaluation of hypersonic inlet flow with nose bluntness, which targets the combined advantages of CFD and method of characteristics. Both the accuracy and efficiency of the developed CCM were verified reliably, and it was well demonstrated for the external surfaces design of a hypersonic forebody/inlet with nose bluntness. With the help of CCM method, effects of nose bluntness on forebody shock shapes and the flowfield qualities which dominate inlet performance were examined and analyzed on the two-dimensional and axisymmetric configurations. The results showed that blunt effects of a wedge forebody are more substantial than that of related cone cases. For a conical forebody with a properly blunted nose, a recovery of the shock front back to that of corresponding sharp nose is exhibited, accompanied with a gradually fading out of entropy layer effects. Consequently a simplification is thought to be reasonable for an axisymmetric inlet with a proper compression angle, and a blunt nose of limited radius can be idealized as a sharp nose, as the spillage and flow variations at the entrance are negligible, even though the nose scale increases to 10% cowl lip radius. Whereas for two-dimensional inlets, the blunt effects are substantial since not only the inlet capturing/starting capabilities, but also the flow uniformities are obviously degraded.

Aerodynamic Heating of a Hypersonic Projectile with Forward-Facing Ellipsoid Cavity at Nose

Numerical experiments are carried out using a commercially available computational-fluid-dynamics code to investigate the aerodynamic heating of a hemisphere–cylinder with a forward-facing ellipsoid cavity at nose in atmosphere. A wide range ellipsoid cavity of depths varying between 3 to 30 mm placed axisymmetrically at the nose of the blunt body with base diameter 40 mm and overall length 70 mm have been investigated. The ratios of semimajor axis to semiminor axis of these cavities () are 3, 2, or 1.5, where semimajor axis a is equal to the depth of cavity and the semiminor axis is close to the lip radius of the cavity. All computations have been done at a freestream Mach number of 10.1 and static pressure and temperature of 16,066 Pa and 216.65 K respectively. The steady-state solutions of axisymmetric Navier–Stokes equations are obtained using a time marching approach in order to study the aerodynamic heating of a hypersonic projectile with a forward-facing ellipsoid cavity at a nose. The simulation results suggest that, though the stagnation-point heat flux and the total heat-transfer rates to the blunt body can be favorably reduced by the introduction of ellipsoid cavity, the local heating at lip can become drastically high.

Effect of orifice inner lip radius on synthetic jet efficiency

A synthetic jet is formed by periodic oscillation of a fluid through an orifice. The oscillatory motion is driven by a diaphragm or other driver. Previous studies have demonstrated that synthetic jet formation and time-averaged cavity pressure are a function of the orifice shape. Traditionally, the performance of the jet is evaluated with varying configurations of fixed driver input voltage or fixed driver displacement. Neither of these measures accurately reflect the efficiency of the actuator. Defining efficiency as “desired output divided by required input,” these traditional measures may not account for increase in required driving current or force. A sharp inside edge of a thin synthetic jet orifice can result in separated flow and increased momentum flux (due to the decreased flow area) for a fixed driver displacement. This can lead one to believe that efficiency has been improved, when, in reality, much more power was required for the driver. Acoustic power, which is the time-average of volume flow rate through the orifice multiplied by the driving pressure, accurately accounts for the power required to drive the actuator. For any synthetic jet actuator, the power to the driver is the power to the fluid (acoustic power) divided by the driver efficiency. If we assume that the driver efficiency is not a strong function of the load, any change to the acoustic power will result in the same proportional change in the driver input power. This study investigates the efficiency of a round (axisymmetric) synthetic jet actuator as a function of the radius of curvature of the interior edge of the orifice. Simultaneous particle image velocimetry measurements at the jet exit and cavity pressure measurements are used to measure the acoustic power required to generate the jet. The resultant momentum flux of the jet is used as a measure of output of the jet. Results are obtained for a range of displacement amplitudes (or stroke lengths) and radii of curvature, while Reynolds number is held fixed.

Edge‐loading severity as a function of cup lip radius in metal‐on‐metal total hips—A finite element analysis

While favorable tribological properties and allowance for larger femoral head sizes have made metal-on-metal (MoM) bearings an increasingly popular choice for total hip arthroplasty, concerns have mounted regarding adverse reactions to metal wear debris and ions. MoM cups differ from conventional polyethylene cups in terms of edge profile design and reductions from full hemisphericity, suggesting differences in loading at or near the cup edge, especially during subluxation events. Finite element analysis was used to investigate the effects of cup orientation and lip edge curvature on damage propensity for edge or near-edge loading during subluxation. Increased cup lip radius (resulting in reduced articular arc) had a detrimental effect upon subluxation-free hip range of motion and upon dislocation resistance. Contact stresses near the cup edge demonstrated complex relationships between edge radius and cup orientation, with peak stresses being influenced by both variables. The tendency for scraping wear at the egress site demonstrated similarly complex dependencies. These data indicate that acetabular cup design is an important determinant of edge and near-edge loading damage propensity.

Two-layer tensioned-web-over-slot die coating: Effect of die lip geometry

Tensioned-web-over-slot die coating (TWOSD) takes advantage of the elastohydrodynamic interaction between the curved web under tension and the coating liquid to sustain a very small coating gap that enables ultra thin coating at relatively high speed. When the product requires two liquid layers, dual slot TWOSD coating can be used to coat those layers simultaneously. In this case, the liquid pressure along the coating bead sets not only the web configuration and meniscus locations but also the interlayer separation point. An easy way to control the pressure distribution is through the die lip geometry. Here, we analyze the effect of four different die lip geometric parameters, e.g. the downstream lip radius, the mid lip radius, the downstream lip offset and the mid lip apex point, on the coating window of the dual slot TWOSD coating. Using the model proposed by Nam and Carvalho (2009c) and a direct tracking of flow features, the boundaries of the vortex-free operating window, area inside the parameter spaces that ensure a uniform coating without vortex inside the flow, were obtained and compared for each die lip configuration. We found that the mid lip radius is one of the important parameters to control the location of the upstream meniscus. Also the location of the interlayer separation point can be controlled by the lip offset and location of the apex point.

Use of an axial nose-tip cavity for delaying ablation onset in hypersonic flow

A forward-facing cavity is examined as a means of reducing the severe heating and delaying ablation onset at the nose-tip of a hypersonic vehicle. Whereas previous studies have concentrated on the nature of flow-induced Hartmann-whistle oscillations or on heating rates alone, the present study addresses the effect of the cavity on ablation onset times through experiments and coupled flow field/heat conduction simulation. Using our previously developed experimental technique, a parametric study is undertaken to optimize the forward-facing cavity geometry for the most delayed ablation onset. The geometric parameters of cavity length, lip radius and diameter are independently optimized for a given nose-tip diameter. Then using benchmarked linked flow field/heat conduction simulations, numerical simulations are conducted for each parametrically optimized configuration in order to investigate the flow physics. The impact of the forward-facing cavity on aerodynamic drag is also considered.

A new noniterative algorithm for computing acoustically constrained vocal tract area functions

We describe a new noniterative algorithm for generating the unique area function determined by the vocal tract length, the lip radius, and the spectral pair consisting of poles of the transfer function and zeros of the input impedance function. Our analysis is restricted to the class of piecewise-constant area functions defined on an even number of equal length intervals. The resulting algorithm involves fewer floating point operations per evaluation than the analogous method of Paige and Zue (1970).

Refractory graphite skimmers for supersonic free-jet, supersonic arc-jet, and plasma discharge applications

The fabrication of molecular beam “skimmers” from electrical discharge machining (EDM) graphite is reported. EDM graphite is highly refractory and is easily machined using conventional cutting and grinding techniques. In its most fine-grained form, EDM graphite can be machined free-standing to a knife-edge lip radius of ∼1 μm, providing excellent skimmer aerodynamics. Being refractory, such EDM skimmers are of particular interest in sampling or collimating high-temperature plasma discharges. Our explicit application is in skimming an electrical discharge supersonic free-jet of molecular nitrogen, forming a molecular beam of A 3Σu+ metastable N2 to be used in the heteroepitaxial growth of III–N wide-band-gap semiconductors. In view of the their economy, ease of manufacture, and excellent aerodynamics, the skimmers may also find use in skimming conventional, nondischarge supersonic free-jets. The performance of the EDM skimmers was tested in a conventional helium supersonic free-jet expansion, measuring the time-of-flight distribution and beam intensity as a function of nozzle pressure and nozzle-skimmer separation. Direct comparison with commercial nickel and copper skimmers showed the EDM graphite skimmers to perform nearly as well as the best commercial metal skimmers. The refractory properties of the skimmers were tested in a high-temperature arc-discharge supersonic free-jet expansion of 10% nitrogen in argon. Exposure to a plasma plume of ∼7500 K for over 6 h produced only relatively minor deterioration of the EDM graphite skimmer.

A study of silicon-wafer surface evaluation using atomic force microscopy

This paper presents a new method of evaluation of silicon-wafer surface roughness. Atomic force microscopy is chosen over conventional methods because of improved horizontal resolution. In this study, the authors investigate (i) the influence of the lip radius on AFM resolution, and (ii) the relationship between AFM and particle counters. The surface roughness of polished silicon wafers is measured by AFM and the influence of different types of polishing pad and colloidal slurry is discussed.

Shock interference prediction using direct simulation Monte Carlo

The shock interaction produced when an incident shock impinges on an inlet cowl lip is investigated for a cowl lip radius of 0.1 in. and flight conditions of Mach 15 and 35-km altitude. This problem is of interest in the design of hypersonic flight vehicles because the interference heating at the cowl lip surface from such a shock interaction is expected to be very high and the design of adequate thermal protection in this region will be challenging. Noncontinuum effects may be significant at this combination of altitude and small dimensions. If this is so, a computational solution based on the Navier-Stokes equations could significantly overpredict the surface heating on the cowl lip. Therefore, a kinetic theory solution technique, direct simulation Monte Carlo (DSMC), is used to predict the flowfield and surface heating. The details of modeling this problem and some preliminary results are presented. The same qualitative flow patterns are seen with DSMC and a continuum solution of the shock interference case, but the peak heating predicted with DSMC is somewhat lower.

Fluctuations in the oscillation of the flue organ pipe—the unsteady steady state

Although the oscillation frequency of a flue organ pipe can usually be measured within 1% or less, observations of the signal with an oscilloscope may show small, apparently random fluctuations in the waveform. These fluctuations have been investigated with a model pipe having a specially designed flue to discharge turbulence below the jet opening. Nonperiodic fluctuations in the fundamental amplitude are found by digital signal processing. For example, the fluctuations are 1–2% for these conditions: Resonator section, 38 × 57 mm; length, 360 mm; lip height, 6.5 mm; jet opening, 0.6 mm; lip radius 0.2 mm; and supply pressure 45‐mm water. The instability is attributed to interaction between the resonator feedback mechanism and the edge‐tone feedback mechanism. (The tone has a “sizzle” which is commonly regarded as a vestigal edgetone effect.) The “partials” near the edgetone frequency (about four times the speaking frequency in this case) are shown to be effectively noise bands. Successive amplitude samples from this region have significant cross correlation with those from the fundamental.

Design of Maximum Thrust Plug Nozzles for Fixed Inlet Geometry

Abstract : The techniques of the calculus of variations were used to determine the configuration of an optimum thrust plug nozzle. The problem is formulated for a fixed thrust injection angle and cowl lip radius, and the resulting plug contour is then an optimum for a given upstream geometry. The optimum values of the injection angle and cowl lip radius are determined by a parametric study. The analysis is carried out for rotational and irrotational flows and includes boundary layer effects. A method is presented for each of the problem formulations to determine if a given contour is an optimum and a relaxation technique is used to obtain a solution to the irrotational flow problem. A computer program which makes use of the design equations for the irrotational flow problem is developed and described. This program is used to carry out a parametric study to determine the optimum cowl lip radius and injection angle when the plug length is fixed. The resulting optimum nozzle is compared to one designed by Rao's Method. The importance of determining the base pressure accurately is illustrated and an example of scramjet nozzle optimization is presented. (Author)