Propulsion and Power Research最新文献

Extraction of biodiesel from waste cooking oil, jatropha, and corn oils is done by transesterification. Diesel and biodiesel were blended at 20% volume ratio to make methyl ester. At doses of 25, 50, and 100 mg/l, carbon nanotubes (CNTs) was mixed with biodiesel blend. The objective of the present research is to examine experimentally a diesel engine performance, combustion characteristics, exergy and emissions analyses with inclusion of nano additive to various methyl ester feedstocks. Methyl ester blend is enriched with CNTs as JB20C100, WB20C100 and CB20C100 where the improvements in thermal efficiency are raised about biodiesel mixture by 9%, 13% and 15%, respectively. Addition of 100 ppm of CNTs to biodiesel blends achieves the greatest reductions in CO (14%, 22% and 30%), HC (16%, 20% and 25%), and smoke emissions (15%, 19% and 23%) for JB20C100, WB20C100 and CB20C100, respectively. By comparing with B20, blending 100 ppm CNTs with JB20, CB20, and WB20 obtained the highest increases in cylinder pressure of 3%, 5%, and 10%, as well as the highest increases in heat release of 4%, 7%, and 11%, respectively. The downside of CNTs addition achieves a rise in NO_x emissions by 10%, 17%, and 22% for JB20C100, WB20C100, and CB20C100, respectively. Exergetic efficiency increases by 8%, 19%, and 24% for B20T100, B20A100, and B20C100, respectively. Sustainability index improvements achieve 1.5%, 5% and 6.5%, for B20T100, B20A100, and B20C100, respectively. WB20 with CNTs of 100 ppm is highly recommended for improving engine performance, combustion, and exergy characteristics with considerable emissions reduction.

The main objective of this work is to investigate the effect of windage heating on the micro high-speed rotor-stator cavity. The influences of centrifugal force and spacing on the windage heating are analyzed with and without the change of gap ratio respectively. The results demonstrate that there is no difference in the flow structure between micro and large-scale rotor-stator cavities at the same rotational Reynolds number and gap ratio. However, the windage heating induced by the larger centrifugal force and smaller spacing brings the different heat transfer laws for the micro rotor-stator cavity. The larger centrifugal force weakens the local heat transfer near the rotor periphery. Such influence can be strengthened at higher rotational Reynolds numbers and lower rotor excess temperatures. Besides, the smaller spacing further enhances the windage heating and reduces the average heat transfer especially under the condition of lower gap ratio. The findings of this work contribute to the design of rotor-stator cavity utilized in the micro rotating machinery.

Tip clearance leakage flow of the turbine bade is an important factor limiting the augment of the high pressure turbine efficiency, which should be suppressed utilizing certain methods. However, the passive control method with the traditional structure is more and more difficult to satisfy the suppressing ability of the advanced turbine demand. In the present paper, a synergetic suppressing method by combining the approach of blade shape modification and spontaneous injection is adopted, to construct a novel tip structure. The aerodynamic characteristics of the tip leakage flow (TLF) with different blade tip configurations, such as the squealer, squealer-winglet (SW) and squealer-winglet-spontaneous injection holes (SWS) composite configurations, are numerically investigated. The impacts of several key geometric parameters, such as the winglet width and the space ng of spontaneous injection holes, are also discussed. Due to the adjustment of the winglet, the SW tip configuration can get better suppressing effect on TLF than the squealer tip. The SWS synergetic suppression tip decrease the leakage flow rate and the leakage mixing loss on the basis of the SW tip due to the blocking effect of the spontaneous injection flow. The key geometric parameters study shows that the suppressing effect of the TLF can be improved by reasonably increasing the winglet width and reducing the spacing between spontaneous injection holes.

In this study, exergy dynamic and advanced exergy analyses are applied to the turbojet engine to assess its mexogenous, endogenous, exogenous, avoidable and unavoidable exergies under the environment conditions of 15 °C temperature and 1 bar pressure. The maximum exergy point in the turbojet engine is found for the combustor in which C₁₁H₂₃ (Jet-A1) fuel is combusted with air, while the minimum one is determined for the air compressor head where the free air enters. The combustion chamber has the maximum fuel, product and irreversibility rates and the air compressor has the minimum fuel and product exergy values, while the minimum irreversibility is found for the turbine. Maximum improvement potential rate is found for the combustion chamber (5141.27 kW), while minimum rate is determined for the turbine of system (6.95 kW). Also, the turbine component has the highest exergy efficiency (97.20%) due to its expansion process, while combustion chamber component has the lowest exergy efficiency (55.39%) due to low efficient combustion process of the fuel. Furthermore, the mexogenous exergy destructions from maximum to minimum are found for the combustion chamber, air compressor and gas turbine units, respectively. Considering exergy dynamic analysis, the mexogenous exergy destruction rates of the combustion chamber, air compressor and gas turbine are found as 184.4 kW, 103.97 kW and 9.99 kW, respectively. Considering all results, the combustion chamber is the primer component to be handled for better efficiency and improvement.

Flow over yawed and unyawed blunt bodies often occurs in various engineering applications. The fluid flow over a yawed cylinder explains the practical significance of subsea applications such as transference control, separating the boundary layer above submerged blocks, and suppressing recirculating bubbles. The current study uses viscous dissipation to analyze the mixed convective hybrid nanofluid flow around a yawed cylinder. Unlike the standard nanofluid model, which only considers one type of nanoparticle, this work considers the hybridization of two types of nanoparticles: alumina (Al₂O₃) and magnetite (Fe₃O₄). A model was developed to investigate the heat transport behaviour of a hybrid nanofluid while accounting for the solid volume fraction. The flow problem is modelled in terms of highly nonlinear partial differential equations (NPDEs) subject to the appropriate boundary conditions. Then appropriate non-similar transformations were used to non-dimensionalize the governing equations. Furthermore, the non-dimensional governing equations were solved using the finite difference method (FDM) and the quasilinearisation technique. The effects of water and nanoparticle concentrations on the velocity and the temperature patterns were illustrated graphically. The hybrid nanofluid reduces the velocity distribution in the spanwise and chordwise directions while increasing the surface drag coefficient. The hybrid nanofluid's fluid temperature and energy transport strength was higher than the base fluid and nanofluid. Also, the temperature of the fluid rises as the energy transfer strength diminishes due to an increase in the Eckert number, which characterizes viscous dissipation. However, when the yaw angle increases in the chordwise and spanwise directions, so does the fluid's velocity. The new outcomes were compared to previously published research and were in good agreement.

Turbofan engine intakes are designed to provide separation-free flow at the fan face over a wide range of operating conditions. But at some off-design conditions, like at high flight speeds and high angles of attack (AoA), the aero engine intake may encounter flow separation. This boundary layer separation inside the nacelle inlet of an aircraft engine can lead to a large number of undesirable outcomes like reduction in fan efficiency, engine stall and high levels of stress on the fan blades. Active flow control is a promising solution to reduce inlet boundary layer separation and the associated fan-face flow distortion at such off-design conditions. By blowing pressurized air into the intake near the separation point, the boundary layer is energized and separation can be controlled. This study investigates the applicability of lip blowing, an active flow control technique, to control intake separation and flow distortion at the fan-face. First, intake separation was triggered in a 3D CFD model based on the NASA Common Research Model (CRM) using high AoA cases at cruise condition (Mach number 0.85, Mass flow capture ratio ∼0.7) and the features of separated flow were analyzed. Thereafter, active flow control was introduce to the intake in the form of two types of lip blowing, direct and pitched blowing. The efficacy of lip blowing at achieving separation control in an ultra high bypass ratio turbofan engine intake has been established through this study. The present paper also examines the significance of blowing parameters like the type of blowing, blowing pressure ratio, and blowing slot dimension, at different angles of attack to identify the critical control parameters. Our research successfully establishes proof of concept by demonstrating the feasibility of using lip blowing for separation control in aero-intakes, via numerical modelling. Furthermore, this study also provides crucial insights regarding the important variables to be considered for future experimental studies, and also for detailed studies covering a wider range of operating and blowing conditions.

The present study proposes ethanol-nitromethane mixture as a safe, storable, and low toxic monopropellant for a gas generator cycle air turbo ramjet engine and evaluates its propulsion performance. The present study proposes that nitromethane is mixed with ethanol to adjust gas generator combustion temperature. The author developed the computational code for the present analysis and verified its accuracy. The specific thrust of ethanol-nitromethane is nearly identical to that of ethanol-liquified oxygen and is higher than methanol-hydroxylammonium nitrate aqueous solution and hydrazine. Hydrazine has the highest Isp among the propellants in the present analysis. However, Isp of ethanol-nitromethane is nearly equal to that of ethanol-liquified oxygen and higher than those of methanol-hydroxylammonium nitrate aqueous solution, and hydroxyl terminated polybutadiene-ammonium perchlorate. With the propellant-to-air ratio range in the present study, ethanol-nitromethane has the stoichiometric condition at the ram combustor around the propellant-to-air ratio range from 0.2 to 0.25 and can obtain high ram combustion temperature. This result is favorable for ethanol-nitromethane because it improves the specific thrust and the specific impulse. Therefore, ethanol-nitromethane can be a promising low-toxic liquid monopropellant for the air turbo ramjet engine.

The primary determination of this study is a numerical investigation of the entropy generation (EG) in the steady two-region flow of viscous fluid and hybrid nanofluid (NF) in a long-infinite vertical annulus having a clear region as well as porous media. Stoke’s and single-phase NF models are used to study the viscous fluid and hybrid nanofluid (HNF) heat transfer developments, respectively. Two types of nanoparticles are taken, such as copper (Cu) and silver (Ag) within base fluid water to make it a HNF. Darcy-Brinkman law is also used to examine the flow through the porous zone in the annulus. Necessary quantities have been used in the system of equations to transfer them into non-dimensional forms. For momentum and energy transport, the numerical results are evaluated for various model parameters and are examined via the shooting method in MATHEMATICA. It is noted that the momentum and energy transport are more significant when two immiscible fluids in a clear vertical annulus are taken. The findings also indicate that two-phase momentum and heat flow are greater when a NF is used in Region-II and lower when a HNF is used. The temperature (in Region-II) falls with a high nanomaterials volume fraction (see Figure 4) while it is increased when the Hartman number is increased. Moreover, velocity declines with increment in nanomaterials volume fraction. Thus, higher thermal conductivity can be accomplished by using a magnetic field.

The windward bend lattice frame structure (WB structure) is characterized by a high heat transfer coefficient and low friction factor. The WB structure can be applied for thermal protection system, protecting outer walls of afterburner and nozzles from being damaged by the heating load of hot gas, for air cooling system of the power battery module, dissipating the heat generated during its charging and discharging. In this paper, the heat transfer characteristics of the windward bend lattice frame structure have been comprehensively studied. A systematic 3D numerical simulation has been conducted to investigate the effects of the structural parameters of the WB structure, including the pitches in both flow direction and transverse direction, the diameter and the inclination angle of windward bend ligament, on its flow resistance and heat transfer enhancement, which has been evaluated by comparing its Nusselt number under an equal pumping power. Furthermore, the contribution of an important parameter, i.e., the ratio of the interstitial heat transfer rate to the end-wall heat transfer rate ($R_Q$), to the overall heat transfer rate has been fully discussed. As a result, the case of 6 units in the longitudinal direction and 2.5 units in the transverse direction, i.e. ($n_x$ = 6, $n_z$ = 2.5) exhibits the best performance in the light of the value of the Nusselt number. Moreover, the structure with a ratio of $R_Q$ ranges in 4.5–5.0 achieves a better heat transfer performance. Finally, two color contour graphs showing an optimal range of Nusselt number coordinated by unit numbers ($n_x$, $n_z$) for pumping powers of 2500 and 3000 have been presented. The graphs correctly reflect the variation of Nusselt numbers of structures with different $n_x$ and $n_z$, and the conclusions remain consistent with the discussion in sections 4.2 Effects of the number of units in the streamwise and spanwise directions, 4.3 Ratio of interstitial heat transfer rate to end-wall heat transfer rate, instructing the reasonable selection of structural parameters of a thermal protection system embedded with WB structure.

Modern gas turbines work under demanding high temperatures, high pressures, and high rotational speeds. In order to ensure durable and reliable operation, effective cooling measures must be applied to the high-temperature rotating components, including turbine blades and turbine disks. Cooling technology, however, is one of the most challenging problems in this field. The present work reviews the current state of cooling technology research, at both the fundamental science and engineering implementation levels, including modeling and simulation, experiments and diagnostics, and cooling technologies for blades and disks. In numerical simulation, the RANS approach remains the most commonly used technique for flow-dynamics and heat-transfer simulations. Much attention has been given to the development of improved turbulence modeling for flows under rotation. For measurement and diagnostics, advanced instrumentation and rotating-flow test facilities have been developed and valuable experimental data obtained. Detailed velocity and temperature distributions in rotating boundary layers have been obtained at scales sufficient to resolve various underlying mechanisms. Both isothermal and non-isothermal conditions have been considered, and the effects of Coriolis and buoyancy forces on flow evolution and heat transfer quantitatively identified. Cooling technologies have been improved by optimizing cooling passage dsigns, especially for curved configurations under rotation. Novel methods such as lamellar cooling and micro-scale cooling were proposed, and their effectiveness evaluated. For disk/cavity cooling, efforts were mainly focused on rotor-stator systems, with special attention given to the position of air injection into disks.