Assessment of conventional and air-jet wheel deflectors for drag reduction of the DrivAer model

Aerodynamic drag is a large resistance force to vehicle motion, particularly at highway speeds. Conventional wheel deflectors were designed to reduce the wheel drag and, consequently, the overall vehicle drag; however, they may actually be detrimental to vehicle aerodynamics in modern designs. In the present study, computational fluid dynamics simulations were conducted on the notchback DrivAer model—a simplified, yet realistic, open-source vehicle model that incorporates features of a modern passenger vehicle. Conventional and air-jet wheel deflectors upstream of the front wheels were introduced to assess the effect of underbody-flow deflection on the vehicle drag. Conventional wheel-deflector designs with varying heights were observed and compared to 45∘ and 90∘ air-jet wheel deflectors. The conventional wheel deflectors reduced wheel drag but resulted in an overall drag increase of up to 10%. For the cases studied, the 90∘ air jet did not reduce the overall drag compared to the baseline case; the 45∘ air jet presented drag benefits of up to 1.5% at 35 m/s and above. Compared to conventional wheel deflectors, air-jet wheel deflectors have the potential to reduce vehicle drag to a greater extent and present the benefit of being turned off at lower speeds when flow deflection is undesirable, thus improving efficiency and reducing emissions.

DETERMINING THE AERODYNAMIC CHARACTERISTIC OF A MINE AXIAL FAN WHEN OPERATING IN REVERSIBLE MODE

This paper describes the procedure for determining the approximate aerodynamic characteristics of a fan operating in a reversible mode with the reverse direction of impeller rotation and deployed position of the straightener blades. To calculate the aerodynamic characteristic, the results of computational modeling of the flow around a flat cascade of airfoil blades were used. To check the adequacy of the applied design models, the comparison of flow deflection angles and total pressure losses when flowing around flat cascades composed of NACA65 airfoils in the direct mode and the known experimental data was made. Using the example of a OV-103 fan made according to the design of Central Institute of Aerohydrodynamics, with the known experimentally obtained aerodynamic characteristic of the reversible mode, the angles of reverse flow deflection in a cascade at the middle radius and total pressure loss in it were calculated. The obtained data were used to calculate the values of the coefficient of total fan pressure depending on the flow rate of air flowing through the fan. The obtained characteristics showed the value of maximum air flow rate higher than in the experimental characteristics. But in this case, it is closer to experimentally obtained data than the value calculated from the known theoretical characteristics of flat cascades.

Profile Loss Investigations With a S-CO2 Axial Turbine Aerofoil

Axial turbines are being extensively designed for supercritical carbon-di-oxide (S-CO2) Brayton cycle power blocks. But very little information is available in the open literature on the aerodynamics of S-CO2 axial turbines, their aerofoils and loss mechanisms. The understanding of real gas behavior of S-CO2 inside a turbine is still very far from complete. Profile losses contribute to more than 50% of overall losses in a turbine. Hence, estimation of profile losses at the outset of the design process is very important. In the present study, the mean section aerofoil of the first stage of a 5 MWe Brayton cycle high temperature turbine is investigated for profile loss characteristics. The basic aerodynamic characteristics of the aerofoil in a linear cascade were initially studied using CFD simulations and cascade test experiments with air as the fluid medium. The aerofoil cascade is then subjected to numerical simulations with S-CO2 as the fluid medium. CFD simulations were carried out using a commercial RANS solver with SST k-ω turbulence model for closure. Air was modelled as ideal gas and S-CO2 was modelled as real gas with Refrigerant Gas Property tables generated over the appropriate pressure and temperature ranges using NIST Refprop database. Losses are also calculated using Craig and Cox loss model. Experiments were carried out by testing a linear cascade model comprising 12 two dimensional blades, in a high-speed cascade wind tunnel. Cascade tests were carried out over a range of exit Mach numbers and incidence angles with air as the working medium. Losses, flow deflection and blade loading were measured during the experiments. Scaling of the profile losses between air and S-CO2 fluid mediums were examined over a range of Mach numbers, Reynolds numbers and incidence angles. Detailed analysis of data generated from numerical simulations, experiments and loss model (mainly in the transonic regime) are discussed in this paper. Losses with S-CO2 was 1.5% lower than that of air while the flow deflection roughly remained the same.

Modeling And Performance Analysis of A Centrifugal Impeller of Water Pump

An impeller is a rotating component equipped with vanes or blades used in centrifugal pumps. Flow deflection at the impeller vanes allows mechanical power (energy at the vanes) to be converted into pump power output. Impeller of a centrifugal pump, usually made of iron, steel, bronze, brass, aluminum or plastic, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. A significant improvement is required for impeller design to resist corrosion, Erosion & weight less. The present work is to design, performance of centrifugal impeller made of Poly-phenylene Sulphide (PPS) and Cast Iron materials and compared the results. Centrifugal impeller is modeled in Solid works, and that model is imported in Ansys-Software, using Ansys-Software we investigated Static and Dynamic behavior of impeller and found that the impeller with Polyphenylene Sulphide (PPS) material is best compared to Cast Iron.

Front-orography interactions during landfall of the New Year's Day Storm 1992

Although following a common synoptic evolution for this region, the New Year's Day Storm 1992 was associated with some of the strongest winds observed along the Norwegian West Cost. The narrow wind band along its bent-back front became famous as the poisonous tail, and paved the way towards today's sting jet terminology. This article re-examines the storm's landfall with a particular focus on the interaction with the orography. Sensitivity analyses based on WRF simulations demonstrate that the formation and the evolution of the warm-air seclusion and its poisonous tail are largely independent from orography. In contrast, the warm sector of the storm is undergoing considerable orographically induced modifications. Both warm and cold fronts are eroded rapidly, and the warm sector is lifted over the orography, thereby accelerating the occlusion process. The insensitivity of the warm-air seclusion to the orographic modifications of the warm sector raises the question to which extent these entities are still interacting after the onset of the occlusion process. Further, we observe ubiquitous and large-amplitude internal gravity waves (IGWs) during the landfall of the warm and cold fronts, exceeding in amplitude the cross-frontal circulation. As the spatial scales of the IGW pattern and of the fronts are comparable, we speculate that wave-front interactions might have contributed to the rapid erosion of the cross-frontal temperature gradient over the orography. Further, IGWs might also provide a plausible cause for the observed near-instantaneous flow deflection around orography at 500 hPa, well above crest height.

Analysis of Damping Derivatives for Delta Wings in Hypersonic Flow for Curved Leading Edges with Full Sine Wave

In this study, an attempt is made to evaluate the effect of first arched ends on the damping derived due to the pitch rate aimed at the variable sine wave bounty, flow deflection angle δ, pivot position, and the Mach numbers. Results show that with the escalation in the bounty of the complete sine wave (i.e., positive amplitude) there is an enlightened escalation in the pitch damping derivatives from h = 0, later in the downstream in the route of the sprawling verge it decreases till the location of the center of pressure and vice versa. At the location where the reasonable force acts, when we consider the stability derivatives in damping for the rate of pitch q, there is a rise in the numerical tenets of the spinoffs. This increase is non-linear in nature and not like for position near the leading edges. The level of the stifling derivatives owing to variations in Mach numbers, flow bend approach δ, and generosity of the sine wave remained in the same range.

Damping Derivative Evaluation in Pitch for an Ogive at High Mach Numbers

In this paper, the formulae for damping derivative for an ogive with the suppositions of a curve on the conical nose. The damping derivative in pitch is assessed for a broad scope of the inertia levels and the flow deflection angle. The outcome indicates that there is a progressive increase in the damping derivative with an increase in the flow deflection angle. When the inertia level is increased from M = 5 to 9, the damping derivative value diminishes, it becomes independent of inertia level, and later any increase in the Mach number does not yield any change in the magnitude of the damping derivatives, and that indicates the attainment of the Mach number independence principle. It is found from the results that when ogive is superimposed, the positive slope is useful, whereas, the negative slope does not yield any useful results, hence must be avoided in the design of the nose part of the aerospace vehicle design. Due to both either positive or negative slope, there is a considerable shift in the Centre of the pressure of the nose, which is right from the dynamic stability point of view. When the slope increased beyond λ > 10, the pressure distribution is such that the magnitude of the damping derivatives attains very peculiar behavior, and this trend is not acceptable. Hence, such a high value of the λ must be avoided.

Experimental Investigation on Flow Past Two and Three Side-by-Side Inclined Cylinders

A series of experiments were conducted to investigate the effect of the inclination angle of the cylinders on the wake flow characteristics for flow past two and three side-by-side inclined cylinders using the particle image velocimetry (PIV). Depending on the inclination angles, purely deflected gap flow, no-deflection gap flow, and flip-flop gap flow patterns are identified for both two and three cylinder cases. In both two and three cylinder cases, the flows through the gaps are found to be in purely deflected flow pattern at small inclination angles and flip-flop pattern at large inclination angles. For the three-cylinder case with flip-flop gap flow pattern, gap flows are predominantly in the outward deflection pattern (toward the two side cylinders) and are occasionally deflected inward (toward the middle cylinder). The gap flow deflection angles for all the tested inclination angles of the cylinders are quantified through statistical analysis, in addition to identifying the flow patterns. The deflection angle is found to decrease with increasing inclination angle for both two- and three-cylinder cases, and the outward deflection angle for the three cylinder cases is greater than the deflection angle of the two-cylinder case. The probability density distributions of the deflection angles approximately follow normal distribution. In the two-cylinder case, the mean flow field is asymmetrical about the x-axis when the possibility of the flow deflection toward one side of the gap is greater than that toward the other side.

Numerical Investigation of the Influence of Flow Deflection at the Upper Hood on Performance of Low Pressure Steam Turbine Exhaust Hoods

Most of the world’s power is produced by large steam turbines using fossil fuel, nuclear and geothermal energy. The LP exhaust hoods of these turbines are known to contribute significantly to the losses within the turbine, hence a minor improvement in their performance, which results in a lower backpressure and thus higher enthalpy drop for the steam turbine, will give a considerable benefit in terms of fuel efficiency. Understanding the flow field and the loss mechanisms within the exhaust hood of LP steam turbines is key to developing better optimized exhaust hood systems. A detailed analysis of loss generation within the exhaust hood was done by the authors [1]. It was found that most losses occur at the upper hood and are caused by the swirling flows, which mostly start at the diffuser outlet, especially for the top diffuser inlet sector flows that have a complex path to the condenser. The authors further numerically investigated the influence of hood height variation on performance of an LP turbine exhaust hood [2], which further contributed to the knowledge of the loss mechanisms. With the loss mechanisms in exhaust hoods reasonably well understood, flow deflection at the upper hood is investigated in the current paper. The deflection is aimed at minimizing the intensity of the vortices formed thus reducing the exhaust losses. The deflector configurations analyzed are modifications of the walls of the reference configuration’s outer casing. The numerical models of the reference configuration which are based on a scaled axial-radial diffuser test rig operated by ITSM have already been validated by the authors at design and overload operating conditions and three tip jet Mach numbers (0, 0.4 and 1.2)[1]. Deflector configurations investigated are found to re-direct the flow at the upper hood and minimize the intensity of the swirling flows hence leading to improvement in performance of LP steam turbine exhaust hoods. The best performing deflector configuration is found to give a considerable improvement in performance of 20% at design load and 40% at overload both at tip jet Mach number of 0.4 (corresponding to shrouded last stage blades). At design load and tip jet Mach number of 1.2 (corresponding to unshrouded last stage blades), the improvement is found to be moderate. About 7% performance increase is observed.