Adiabatic Effectiveness Research Articles

Detached-Eddy Simulation of Trailing-Edge (TE) Cutback Turbine Blade Cooling

This research evaluates the cooling performance of trailing-edge cutback for gas turbine blade. By using DES based on SST k-ω turbulence model, numerical investigations were performed at two steps: first, to validate simulation results from an existing TE cutback cooling with staggered pin-fin arrays inside the cooling passage against experimental measurement. Three types structured mesh from coarse (Δy + = 0.74) to fine (Δy + = 1.22) were evaluated during this step; second, to investigate the TE cutback cooling performance on various blowing ratios. Simulations were performed by keeping the same initials and boundary conditions as the experiment. The result indicates that validation can be considered acceptable by controlling grid quality resolution near wall regions. Both computational data of the adiabatic film-cooling effectiveness and the discharge coefficient are in good agreement with available experimental measurements. The averaged film-cooling effectiveness along the cutback region is highly influenced by the blowing ratios, which is to be related to the turbulent flow structures formed at the mixing region as the impact of coolant flow ejection. The increase of coolant jet velocity triggers the heat transfer process up to the downstream region of TE cutback cooling.

Numerical Investigations on Impact of Ogive Nosed Projectiles on Thin Plates

Objectives: Numerical investigations were carried out on 1mm thick aluminum plates against ogive-nosed steel projectiles of 15mm diameter and 55g mass. The finite element code ABAQUS was used to perform Three-dimensional and two-dimensional axisymmetric numerical simulations for the conducted experiment. Methods: The ABAQUS/Explicit finite element code in conjunction with a elasto-viscoplastic material model employed by Johnson-Cook model was used to perform the simulation study. The material model takes in various factors: yielding, linear thermo-elasticity, strain rate hardening, softening due to adiabatic heating, plastic flow, fracture effects and isotropic strain hardening. Both the rigid and deformable projectiles were considered to study their influence on the failure mechanism. Findings: The numerical results thus obtained, when compared with the available experimental results are found to be similar at high incidence velocities. However, at low incidence velocities the numerical results are found to be under predicted. Almost same ballistic resistance was offered by the target plate irrespective of the rigidity of projectile. The residual velocities of aluminum targets obtained using 2D and 3D deformable and rigid projectile curves became almost thesame. Improvements: Based on these studies, the influence of deformable projectile on thin targets was not significant but the energy absorption by the projectile on thick target is to be studied further.

ON THE ISOTROPIZATION OF SOLAR WIND PROTONS

ABSTRACT Protons observed in the solar wind are characterized by temperature anisotropies whose upper and lower bounds can be partially explained by marginal instability conditions associated with various plasma instabilities. However, an outstanding problem is that the majority of data distributed in space are located away from the boundaries and occupy a broad region with the peak near isotropic condition. The present paper employs macroscopic-kinetic theory that includes adiabatic effects arising from various non-monotonic inhomogeneities of magnetic field and density, the influence from proton-cyclotron and parallel firehose instabilities, and collisional dissipation in order to explore the consequence of each effect. It is found that spatial inhomogeneities are the leading cause of the scattering of the data points away from the marginal stability boundaries in space, thus providing a potential explanation for observations.

Adiabatic magnetocaloric effect in Ni50Mn35In15 ribbons

Heusler-type Ni-Mn-based metamagnetic shape memory alloys (MetaMSMAs) are promising candidates for magnetic refrigeration. To increase heat exchange rate and efficiency of cooling, the material should have a high surface/volume ratio. In this work, the typical Ni50Mn35In15 MetaMSMA was selected to fabricate thin ribbons by melt-spinning. The characteristic transformations of the ribbons were determined by calorimetry, X-ray diffraction, scanning electron microscopy and thermomagnetization measurements. The inverse and conventional magnetocaloric effects (MCEs) associated with the martensitic transformation (MT) and the ferromagnetic transition of the austenite (TCA), respectively, were measured directly by the adiabatic method (ΔTad) and indirectly by estimating the magnetic entropy change from magnetization measurements. It is found that the ribbons exhibit large values of ΔTad = −1.1 K at μ0ΔH = 1.9 T, in the vicinity of the MT temperature of 300 K for inverse MCE, and ΔTad = 2.3 K for conventional MCE at TCA = 309 K. This result strongly motivates further development of different MetaMSMA refrigerants shaped as ribbons.

Effect of In-Hole Roughness on Film Cooling From a Shaped Hole

While much is known about how macrogeometry of shaped holes affects their ability to successfully cool gas turbine components, little is known about the influence of surface roughness on cooling hole interior walls. For this study, a baseline-shaped hole was tested with various configurations of in-hole roughness. Adiabatic effectiveness measurements at blowing ratios up to 3 showed that the in-hole roughness caused decreased adiabatic effectiveness relative to smooth holes. Decreases in area-averaged effectiveness grew more severe with larger roughness size and with higher blowing ratios for a given roughness. Decreases of more than 60% were measured at a blowing ratio of 3 for the largest roughness values. Thermal field and flowfield measurements showed that in-hole roughness caused increased velocity of core flow through the hole, which increased the jet penetration height and turbulence intensity resulting in an increased mixing between the coolant and the mainstream. Effectiveness reductions due to roughness were also observed when roughness was isolated to only the diffused outlet of holes, and when the mainstream was highly turbulent.

El Niño, La Niña, and the global sea level budget

Abstract. Previous studies show that nonseasonal variations in global-mean sea level (GMSL) are significantly correlated with El Niño–Southern Oscillation (ENSO). However, it has remained unclear to what extent these ENSO-related GMSL fluctuations correspond to steric (i.e., density) or barystatic (mass) effects. Here we diagnose the GMSL budget for ENSO events observationally using data from profiling floats, satellite gravimetry, and radar altimetry during 2005–2015. Steric and barystatic effects make comparable contributions to the GMSL budget during ENSO, in contrast to previous interpretations based largely on hydrological models, which emphasize the barystatic component. The steric contributions reflect changes in global ocean heat content, centered on the Pacific. Distributions of ocean heat storage in the Pacific arise from a mix of diabatic and adiabatic effects. Results have implications for understanding the surface warming slowdown and demonstrate the usefulness of the Global Ocean Observing System for constraining Earth's hydrological cycle and radiation imbalance.

Ab initio potential energy surface and vibration-rotation energy levels of beryllium monohydroxide.

The accurate potential energy surface of beryllium monohydroxide, BeOH, in its ground electronic state X 2A' has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent core-valence basis sets up to septuple-zeta quality. The higher-order electron correlation, scalar relativistic, and adiabatic effects were taken into account. The BeOH molecule was confirmed to be bent at equilibrium, with the BeOH angle of 141.2° and the barrier to linearity of 129 cm-1 . The vibration-rotation energy levels of the BeOH and BeOD isotopologues were predicted using a variational approach and compared with recent experimental data. The results can be useful in a further analysis of high-resolution vibration-rotation spectra of these interesting species. © 2016 Wiley Periodicals, Inc.

Effects of deposition locations on film cooling with and without a mist injection

ABSTRACTThe adiabatic film-cooling effectiveness on a thermal barrier coating surface is investigated numerically. A film-cooling hole with an inclination angle of 35° is placed upstream the deposition configuration. The depositions are arranged on the external wall with three different positions. For no-mist models, the cooling performances downstream the wall are investigated for the blowing ratios of 0.5, 0.75, and 1.0. Results show that the adiabatic film-cooling effectiveness without surface deposition is decreased by increasing the blowing ratio. To investigate the effects of both different locations and 4.4% mist injection on the film cooling, a discrete phase model (DPM) is used. It is found that the film-cooling effectiveness is improved remarkably from the deposition position to the wall downstream. In addition, deposition formation at the middle location shows a good cooling effectiveness, but the lowest value of the film-cooling effectiveness occurs upstream the deposition position.

Finite element modeling of micro-orthogonal cutting process with dead metal cap

Dead metal cap plays an important role in the microcutting process because target material piled up on the tool–chip–workpiece interface can alter the cutting geometry. The target of this study is to model and simulate the micro-orthogonal cutting process in the presence of dead metal cap in order to investigate the effects of this phenomenon on the micromachining process outputs (cutting force, thrust force and chip thickness) and stress distribution, equivalent plastic strain and temperature inside the workpiece shear zones. For this purpose, the finite element method with explicit dynamic solution and adiabatic heating effect along with arbitrary Lagrangian–Eulerian approach is used. It is shown that the finite element models with current state-of-the-art assumptions cannot take into account the dead metal cap by default. For this reason, dead metal cap is artificially introduced on the rounded tool edge in this study for carrying out a proper analysis. Several simulations with different dead metal cap geometries are performed and obtained results show that prediction of cutting force, thrust force and chip thickness are sensitive to the presence of dead metal cap and its geometry. Micro-orthogonal cutting experiments are carried out on tubular AISI 1045 workpieces for validating and interpreting simulated results. The error between predicted and experimental data is calculated, and it is shown that simulation performances can be improved by considering the dead metal cap into the process model. For example, it is possible to reduce the error to less than 5% in case of thrust force prediction. This study points out how the target material’s Von Mises stress, equivalent plastic strain and temperature distribution are sensitive to any alteration of the edge geometry due to the dead metal cap. The best dead metal cap configuration in terms of agreement with experiments is also the one introducing a more homogeneous distribution of these quantities along the shear plane.

Magnetocaloric effect for inducing hypothermia as new therapeutic strategy for stroke: A physical approach

Hypothermia is an effective neuroprotective strategy for acute stroke. However, in clinical practice, the induction of hypothermia is achieved through the systemic reduction of body temperature (using thermal covers or endovascular cooling devices) which results in a complex system associated in many cases to side effects. Therefore, the aim of this study was to test the magnetocaloric effect as a potential new therapeutic strategy for stroke by means of an adiabatic magnetic refrigerator device.As a first approach, we have developed a simple device to evaluate in vitro the thermodynamic behavior of different concentrations of commercial gadolinium powder as a reference magnetocaloric material. The samples, properly thermally insulated, were cyclically magnetized and demagnetized at room temperature by 1T permanent magnets in order to induce an adiabatic magnetic effect. Under the experimental conditions tested, results showed a maximun non-accumulative temperature variation of 0.2°C, insufficient to carry out an effective hypothermia. This study allowed us to discuss about the use of new materials and strategies for further in vivo experiments.

Effect of Hole Shapes, Orientation And Hole Arrangements On Film Cooling Effectiveness

In this present work, the effect of hole shapes, orientation and hole arrangements on film cooling effectiveness has been carried out. For this work a flat plate has been considered for the computational model. Computational analysis of film cooling effectiveness using different hole shapes with no streamwise inclination has been carried out. Initially, the model with an inclination of 30° has been verified with the experimental data. The validation results are well in agreement with the results taken from literature. Five different hole shapes viz. Cylindrical, Elliptic, Triangular, Semi-Cylindrical and Semi-Elliptic have been compared and validated over a wide range of blowing ratios. The blowing ratios ranged from 0.67 to 1.67. Later, orientation of holes have also been varied along with the number of rows and hole arrangements in rows. The performance of film cooling scheme has been given in terms of centerline and laterally averaged adiabatic effectiveness. Semi-elliptic hole utilizes half of the mass flow as in other hole shapes and gives nominal values of effectiveness. The triangular hole geometry shows higher values of effectiveness than other hole geometries. But when compared on the basis of effectiveness and coolant mass consumption, Semi-elliptic hole came out to give best results.

Computational Fluid Dynamics Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions

The hostile turbine environment requires testing film cooling designs in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low-temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, the density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods best provide scaled film cooling performance. Furthermore, matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of a film cooled leading edge geometry at high-temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low-temperature experimental conditions with a 10× scale model. Matching was performed with three common coolants used in low-temperature film cooling experiments—room temperature air, CO2, and cold air. Results indicate that matched momentum flux ratio is the most appropriate for approximating adiabatic effectiveness for the case of room temperature air coolant, but matching the density ratio through either CO2 or cold coolant also has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches the density ratio.

Classification of materials with divergent magnetic Grüneisen parameter

At any quantum critical point (QCP) with a critical magnetic field , the magnetic Grüneisen parameter , which equals the adiabatic magnetocaloric effect, is predicted to show characteristic signatures such as a divergence, sign change and scaling. We categorise 13 materials, ranging from heavy fermion metals to frustrated magnets, where such experimental signatures have been found. Remarkably, seven stoichiometric materials at ambient pressure show . However, additional thermodynamic and magnetic experiments suggest that most of them do not show a zero-field QCP. While the existence of a pressure insensitive ‘strange metal’ state is one possibility, for some of the materials seems influenced by impurities or a fraction of moments which are not participating in a frozen state. To unambiguously prove zero-field and pressure-sensitive quantum criticality, a divergence is insufficient and also the Grüneisen ratio of thermal expansion to specific heat must diverge.

Film Cooling Modeling for Gas Turbine Nozzles and Blades: Validation and Application

The design of modern gas turbines cooling systems cannot be separated from the use of computational fluid dynamics (CFD) and the accurate estimation of the effect of film cooling. Nevertheless, a complete modeling of film cooling holes within the computational domain requires an effort both from the point of view of the mesh creation and from computational time. It is here proposed a new way to model the film cooling (FCM), capable of representing the effect of the coolant at hole exit. This is possible due to the introduction of local source terms near the hole exit in a delimited portion of the domain, avoiding the meshing process of perforations. The goal is to provide a reliable and accurate tool to simulate film-cooled turbine blades and nozzles without having to explicitly mesh the holes. The model was subjected to an intensive validation campaign, composed of two phases. During the first one, FCM results are compared to experimental data and numerical results (obtained with complete cooling holes meshing) on a series of test cases reproducing flat plate cooling configurations for different coolant conditions (in terms of blowing and density ratio). In the second phase, a film-cooled vane test case has been studied, in order to consider a real injection system and flow conditions: FCM predictions are compared to an in-house developed correlative approach and full conjugate heat transfer (CHT) results. Finally, a comparison between FCM predictions and experimental data was performed on an actual nozzle of a GE Oil & Gas heavy-duty gas turbine, in order to prove the feasibility of the procedure. The presented film cooling model (FCM) proved to be a feasible and reliable tool, able to evaluate adiabatic effectiveness, simplifying the design phase avoiding the meshing process of perforations.

Numerical approach to new tangential slot effect on film cooling effectiveness over asymmetrical turbine blade

The focus of this numerical study is to conceive a new basic film cooling configuration in order to increase film cooling effectiveness, especially at the leading edge zone between the injection holes where cooling is mostly needed. The new configuration, resulting from the tangential slot configuration and especially adapted to the leading edge of an asymmetrical blade, is compared to the uniform slot configuration. Three alternatives geometries were proposed and numerically tested to find the configuration that provides the best film cooling effectiveness. The simulation is conducted at a fixed density ratio of 1.0 and a blowing ratio of 0.7. A new parameter, Rc, is defined to measure the rate of blade coverage by the film cooling. The outcomes of the numerical results indicate that the three proposed configurations allow better thermal protection because of their higher film cooling coverage. At suction side, the new configurations provide a better film cooling coverage than the baseline case. The minimal improvement is at approximately 34%, with a light superiority of case 1. At pressure side, the use of the tangential slot is especially interesting for the allowed minimum adiabatic effectiveness values between 0.3 and 0.5.

Residual stress distribution in a laser peened Ti-2.5Cu alloy

The goal of the present study is to investigate residual stress distributions and the accompanying deformation mechanisms during the process of laser peening without coating (LPwC), carried out on a Ti-2.5Cu alloy at a fixed power density of 6.97 GW cm− 2 with overlap rates from 50 to 90% (in steps of 10%). Thermal softening near surface (confined to a depth of 50 μm) from laser beam-material interaction was observed. Work-hardening increased with increase in overlap percentage till 80%. The maximum residual stress was found to be − 889 MPa for an optimal 70% overlap. Twinning was found to increase with the increase in overlap rates, indicating the hardening of the sample. The combined effect of adiabatic heating and thermal effects at the surface due to laser beam-material interaction (propagating inside the material), results in the softening of the material. The softening was found to be only in the onset stage, without flow localization. Softening predominates hardening beyond the overlap rates of 80% and the implications for this towards multiple peening are discussed.

Phenology and growth performance of Himalayan birch (Betula utilis) in Kashmir Western Himalayas along the different altitudinal gradients

The phenological events, height class distribution, volume and biomass of Himalayan birchor bhojpatra (B. utilis D. Don) were monitored along the altitudinal gradient in distinct ecological settings at Sindh and Tangmarg forest divisions in western Himalayas, Kashmir. The observations recorded revealed high synchrony throughout the altitudinal gradients, especially for bud set, bud burst, peak flowering and seed maturation. All the phenological events began early at lower elevation as compared to higher elevation. The timing of phenophases along the altitude was governed by the timing of snow-melt which is usually responsible for early phenological changes in the northern alpine habitats. The height, volume and biomass showed a decreasing trend with increasing altitude at both the sites. Higher number of trees (116.71 trees/ha) with maximum height, volume (112.38 m3/ha) and biomass (57.31 tonnes/ha) were recorded at 3 000-3 200 m asl. The values for all these parameters decreased with increasing altitude from 3 200-3 400 and 3 400-3 600 m amsl, respectively. The short growing seasons, reduced air and soil temperature (an adiabatic effect), increased exposure to wind, lower availability of nutrients and increased exposure to frost are some of the common features of high altitude niches which greatly influences the growth of the existent vegetation.

Determination of Cooling Parameters for a High-Speed, True-Scale, Metallic Turbine Vane

Facilities such as the Turbine Research Facility (TRF) at the Air Force Research Laboratory have been acquiring uncooled heat transfer measurements on full-scale metallic airfoils for several years. The addition of cooling flow to this type of facility has provided new capabilities and new challenges. Two primary challenges for cooled rotating hardware are that the true local film temperature is unknown, and cooled thin-walled metallic airfoils prohibit semi-infinite heat conduction calculation. Extracting true local adiabatic effectiveness and the heat transfer coefficient from measurements of surface temperature and surface heat transfer is therefore difficult. In contrast, another cooling parameter, the overall effectiveness (ϕ), is readily obtained from the measurements of surface temperature, internal coolant temperature, and mainstream temperature. The overall effectiveness is a normalized measure of surface temperatures expected for actual operating conditions and is thus an important parameter that drives the life expectancy of a turbine component. Another issue is that scaling ϕ from experimental conditions to engine conditions is dependent on the heat transfer through the part. It has been well-established that the Biot number must be matched for the experimentally measured ϕ to match ϕ at engine conditions. However, the thermal conductivity of both the metal blade and the thermal barrier coating changes substantially from low-temperature to high-temperature engine conditions and usually not in the same proportion. This paper describes a novel method of replicating the correct thermal behavior of the thermal barrier coating (TBC) relative to the metal turbine while obtaining surface temperature measurements and heat fluxes. Furthermore, this paper describes how the ϕ value obtained at the low-temperature conditions can be adjusted to predict ϕ at high-temperature engine conditions when it is impossible to match the Biot number perfectly.

Review of Ingress in Gas Turbines

This review summarizes research concerned with the ingress of hot mainstream gas through the rim seals of gas turbines. It includes experimental, theoretical, and computational studies conducted by many institutions, and the ingress is classified as externally induced (EI), rotationally induced (RI), and combined ingress (CI). Although EI ingress (which is caused by the circumferential distribution of pressure created by the vanes and blades in the turbine annulus) occurs in all turbines, RI and CI ingress can be important at off-design conditions and for the inner seal of a double-seal geometry. For all three types of ingress, the equations from a simple orifice model are shown to be useful for relating the sealing effectiveness (and therefore the amount of hot gas ingested into the wheel-space of a turbine) to the sealing flow rate. In this paper, experimental data obtained from different research groups have been transformed into a consistent format and reviewed using the orifice model equations. Most of the published results for sealing effectiveness have been made using concentration measurements of a tracer gas (usually CO2) on the surface of the stator, and—for a large number of tests with single and double seals—the measured distributions of effectiveness with sealing flow rate are shown to be consistent with those predicted by the model. Although the flow through the rim seal can be treated as inviscid, the flow inside the wheel-space is controlled by the boundary layers on the rotor and stator. Using boundary-layer theory and the similarity between the transfer of mass and energy, a theoretical model has been developed to relate the adiabatic effectiveness on the rotor to the sealing effectiveness of the rim seal. Concentration measurements on the stator and infrared (IR) measurements on the rotor have confirmed that, even when ingress occurs, the sealing flow will help to protect the rotor from the effect of hot-gas ingestion. Despite the improved understanding of the “ingress problem,” there are still many unanswered questions to be addressed.

The effects of upstream steps with unevenly spanwise distributed height on rectangular hole film cooling performance

The effects of placing upstream steps with unevenly spanwise distributed height on the film cooling effectiveness are investigated systematically using ANSYS CFX. In this paper, the configurations with steps of five different spanwise distributed height are selected to study the film cooling adiabatic effectiveness, heat transfer characteristics and the flow dynamics in terms of the flow structure, vortex vorticity and total pressure loss. In addition, the configuration without step is also conducted to serve as a comparison and its results are compared with experimental measurements to verify the computational method. Three separate blowing ratios (M=1,1.5,2) are reported for all tests. The results of simulation indicate the averaged cooling effectiveness on the surface1 (which downstream of the upstream steps and around the film cooling holes) decreases as hmid increases. The highest averaged cooling effectiveness on the surface1 of the case with step is 2.21, 2.03 and 1.78 times respectively that of the case without step at M=1, 1.5 and 2. Besides that, the cooling effectiveness on the surface2 (which downstream of the film cooling holes) also decreases with an increase in hmid, and the highest averaged cooling effectiveness on the surface2 of the case with step is 1.51, 1.61 and 1.56 times respectively that of the case without step at M=1, 1.5 and 2. Additionally, the effect of upstream steps on the heat transfer characteristics is also conducted.