Double-wall Configuration Research Articles

Numerical study on cooling characteristics of turbine blade based on laminated cooling configuration with clapboards

The double-wall configuration, characterized by its notable overall cooling effectiveness, serves as a pivotal reference configuration in the design of next-generation turbine blades. In this study, a laminated cooling configuration with clapboards is developed, based on insights derived from both double-wall cooling configuration and laminated cooling configuration. Through a comparative analysis, with the double-wall cooling configuration and laminated cooling configuration as benchmarks, the newly constructed configuration is capable of enhancing overall cooling effectiveness while maintaining control over total pressure loss in the study. Specifically, in the context of external film cooling with an adiabatic condition, the laminated cooling configuration with clapboards attains the highest value at low blowing ratios, while the laminated cooling configuration excels in average adiabatic film cooling effectiveness at high blowing ratios. Importantly, the inclusion of clapboards significantly improves the internal heat transfer area, resulting in a greater internal total heat exchange in the laminated cooling configuration with clapboards. Consequently, this proposed configuration achieves the highest overall cooling effectiveness, achieving increases of 9.02%–14.08 % and 2.77 %–3.54 % relative to the double-wall cooling configuration and laminated cooling configuration, respectively. A comprehensive performance evaluation criterion is applied to assess cooling effectiveness and pressure loss. The results indicate that the laminated cooling configuration with clapboards enhances heat transfer effectiveness while effectively controlling pressure drop, with an evaluation value of over 1.0. Furthermore, the overall cooling effectiveness of the three cooling configurations is compared at two Reynolds numbers. It is found that the proposed configuration exhibits the best cooling performance, especially at the high Reynolds number.

Design and analysis of periodic acoustic metamaterial sound insulator using finite element method

In this article, a design of acoustic metamaterial containing Helmholtz resonators periodically embedded in a porous material is investigated for aerospace applications using the finite element method (FEM). The results obtained using the FEM are compared with the results of the theory, and the proposed transfer matrix method and good agreements are obtained. The transfer matrix method was combined with FEM calculations for two different termination conditions (plane wave radiation and rigid wall) in order to retrieve the equivalent matrix of the porous layer with the integrated periodic resonator. The equivalent matrix is then coupled analytically in series with others matrices. Finite element method studies are carried out on single and double wall configurations, and the effects of different resonator parameters and the air gap on the transmission loss are illustrated. The influences of the orientation of the neck opening and the resistivity of the porous material are also studied. Finite element method results for different incident angles are presented for single and double wall configurations. The proposed design can potentially be integrated into the panels of aircraft cabins in order to reduce the noise level at low frequencies inside the cabin.

Experimental and numerical studies on enhanced effusion cooling with shallowly dimpled film holes on double-wall structure surface

This paper presents a flow and heat transfer investigation on multi-row dimpled film cooling in the double-wall configuration, considering important flow and geometrical characteristics including internal narrow jet impingement channel and outer film cooling with shallowly dimpled holes. The film cooling hole has dimpled exit, with the dimple depth to diameter ratio of 0.2. The inclined angle of the film hole is 30 degree and film hole length to diameter ratio is 3.0. The adiabatic film cooling effectiveness and heat transfer characteristics on the external surface are obtained by using transient infrared thermography measurement technique, which is based on the Impulse Response Method. And steady-state numerical computations using the Shear Stress Transport (SST) k-ω turbulence model were carried out respectively with the experimentally related adiabatic wall boundary conditions and with the fluid–solid conjugated boundary conditions, which provides the turbulent flow structure and overall cooling performance of the double-wall structure. The experimental results indicate that compared to the counterpart cylindrical film holes, the dimpled film holes can expand the spanwise coverage of coolant film, and the adiabatic film cooling effectiveness was improved by 66 %, 82 % and 180 % respectively at BR = 0.3, 0.6 and 1.0. Therefore, the dimpled holes can improve the film cooling effectiveness significantly. The numerical simulations indicated that the dimpled film holes influence the jet-in-crossflow structure and film cooling effectiveness significantly through complex interactions of the coolant jets, mainstream flow and dimpled wall. The overall cooling effectiveness of the double-wall structure with dimpled film holes on the thermal barrier coating can be distinctively improved by about 12.8 % over the case with conventional cylindrical film holes, which was indicated in the conjugated simulations under the blowing ratio of 1.0 and the mainstream-coolant temperature ratio of 2.0.

Modelling of acoustic metamaterial sound insulator using a transfer matrix method for aircraft cabin applications

The incorporation of acoustic metamaterials in the design of aircraft fuselage panels in order to reduce the low frequency noise inside the cabin is nowadays a major research subject in order to offer passengers a comfortable cabin environment. In this study, acoustic metamaterial made of Helmholtz resonators periodically embedded into a porous material is investigated using a transfer matrix approach combined with finite element calculations. This transfer matrix method is based on the two-load methods where the two loads in the numerical simulations are two different termination conditions (plane wave radiation and rigid wall) in order to retrieve the equivalent transfer matrix of the porous layer with embedded periodic Helmholtz resonators. The equivalent matrix is then coupled analytically in series with others analytical matrices to model complex multilayer metamaterials. The results of the transmission loss obtained exclusively using finite element method for single and double wall configurations are compared with the results of the proposed transfer matrix method and good agreements are obtained. It is observed that the frequency band of the transmission loss of the double wall configuration is larger than the one of the single wall configuration with higher transmission loss peak value. The investigated metamaterial can potentially be used in the design of aircraft cabin panels for low frequency noise reduction.

Structural and electronic properties of double wall MoSTe nanotubes.

Janus nanotubes originating from rolling up asymmetric dichalcogenide monolayers have shown unique properties compared to their 2D and 3D counterparts. Most of the work on Janus nanotubes is focused on single-wall (SW) tubes. In this work, we have investigated the structural and electronic properties of double wall (DW) MoSTe nanotubes using Density Functional Theory (DFT). The most stable DW, corresponding to a minimum of the strain energy, is formed by combining 16- and 24-unit cells for the inner and outer tubes. This DW configuration shows a slightly smaller inner diameter than the SW tube, which was formed by 18-unit cells due to the intra-wall interaction. The investigation of the band gaps of 2D structures under strain and SW/DW nanotubes revealed that the curvature of the nanotube and the strain induced when forming the tube are the two primary factors enabling the band gap tuning. Moreover, we found that the band gaps of the DW MoSTe tubes close, compared to the SWs, generating tubes with a metallic-like behavior. This property makes DW MoSTe nanotubes promising for electrochemical applications.

Efficient Design of Thin Wall Seating Made of a Single Piece of Heavy-Duty Corrugated Cardboard.

Corrugated cardboard has waved cores with small flutes that prevent the use of detailed numerical models of whole structures. Many homogenization methods in the literature overcome this drawback by defining equivalent homogeneous plates with the same mechanical behaviour at a macro-mechanical scale. However, few homogenization works have considered complete structures, focusing mainly on beams or plates. For the first time, this study explores the application of homogenization approaches to larger structures as an aid in their design process. We also considered triple-wall boards rather than single- and double-wall configurations commonly addressed in the literature. To this end, we adapted the homogenization methods proposed by Talbi and Duong to analyze thin-walled stools made of triple-wall corrugated cardboard. Using a progressive design process, we performed an efficient stool design by removing material zones with lower stresses, with 35% less material, 35% lower vertical deflections, and 66% lower stresses than the initial design. Unlike other corrugated cardboard stools, this design comprises just one folded piece instead of three, thus saving storage space. These results demonstrate the utility of homogenization techniques as an aid in the design process of whole structures made of corrugated cardboard. Further research will consider buckling analysis.

Theoretical and experimental analysis of overall cooling effectiveness for afterburner double-wall heat shield

The porous heat shield installed in the afterburner can effectively prevent the afterburner cylinder from overheating. Impingement/effusion cooling is one composite cooling technique to effectively improve the overall cooling effectiveness of the heat shield. Designing effective and efficient double-wall configurations requires a detailed understanding of how geometry and operating conditions affect the way coolant cools the afterburner cylinder. In this study, conjugated heat transfer experiments were conducted using IR thermography for double-wall heat shields with three open areas of the impingement plate (σ = 0.5%, 0.7%, 0.8%). The momentum flux ratio was varied in the range 0.01≤I≤0.50. The mainstream Reynolds number, based on the diameter of the film hole, was varied in the range 800≤Reg≤2000. The effects of geometrical and aerodynamic parameters on overall cooling effectiveness were experimentally and numerically investigated with the comprehensive effects of solid heat conduction and convection heat transfer. The experiments were modeled in a low-temperature state (Tg = 603 K, Tc = 298 K), which was based on the analogy theory and matching principle, as if the experiments were conducted under engine operating conditions. The modeling accuracy of experimental results was analyzed by the analogy theory. Results show that the difference in the overall cooling effectiveness between “laboratory” conditions (Tg/Tc = 2) and “engine” conditions (Tg/Tc = 4) is within 0.048. The overall cooling effectiveness is mainly affected by the open area through adiabatic cooling effectiveness and internal heat transfer, and that is mainly affected by the mainstream Reynolds number through external heat transfer. According to the area-averaged results in given experimental conditions, the maximum overall cooling effectiveness raise and drop coefficients after increasing open area and mainstream Reynolds number are 17.3% and 6%, respectively. Thus, the high open area and low mainstream Reynolds number are beneficial to improve the overall cooling effectiveness of the afterburner double-wall heat shield. Furthermore, the experimental measurements provide an important database for the evaluation of computational fluid dynamics simulations of the conjugate heat transfer effects occurring in the double-wall heat shield.

2D and 3D thermoelastic phenomena in double wall transpiration cooling systems for gas turbine blades and hypersonic flight

Double wall transpiration cooling (DWTC) systems allow the operating temperature of gas turbines to be increased beyond current levels, promising further enhancements in engine efficiency and a reduction in fuel consumption and emissions. Alongside the outstanding cooling performance of DWTC systems, there are structural integrity implications that need to be evaluated. Our theoretical and Finite Element (FE) analysis here determine thermal stresses arising in a range of double wall configurations in two-dimensional (2D) and three-dimensional (3D) space. The 3D geometric effects of wall spacing, wall thickness ratio, connecting pedestal spacing between the walls and pedestal thickness are interpreted based on considerations on 2D idealisations. We highlight that although an inner cool wall may be essential for applying internal impingement cooling in the system to enhance its aerothermal performance, at the same time the inner wall increases compression in the hot outer wall, due to the kinematic constraint that the two walls must extend equally. As a result, the critical compressive stresses in the hot wall can be relieved by using a thinner inner wall. Our study determines the essential nominal stress fields that drive stress concentrations and associated local creep-plasticity-fatigue at critical features in DWTC systems, such as effusion holes and pedestals.

Conjugate Heat Transfer Study of Innovative Pin-Fin Cooling Configuration

The Paper involves experimental and numerical heat transfer analyses of four pin-fin cooling configurations in a rectangular channel. Two design concepts were studied with two separate pin-fin (cylindrical and triangular) geometries. The first design includes a single-wall pin-fin configuration where the coolant flows through an array of full-length cylindrical (PF) and triangular pin fins (TF). The second configuration involves a double-wall pin-fin–jet configuration where the coolant jet impinges on the target wall, then flows through the array of partial-length cylindrical pin fins with jets (PFC) and partial-length triangular pin fins with jets (TFC). IR thermography was used to measure the steady state wall temperature of the target surface to estimate the overall cooling effectiveness . A transient heat transfer experiment was conducted to evaluate the internal heat transfer coefficient from the transient wall temperature. It is found that the double-wall pin-fin–jet (PFC and TFC) configurations show higher cooling effectiveness compared to the single-wall pin-fin (PF and TF) designs and the triangular pin fin (TF and TFC) showed a higher heat transfer augmentation compared to the cylindrical pin fin (PF and PFC) design. Numerical study later confirmed that the triangular pin fin creates a pair of streamwise vortices that augments the local heat transfer. The presence of the pin fin in the double-wall configuration prevents the development of a strong crossflow that negatively affects the heat transfer of the impinging jet. In addition, the triangular pin fin not only prevents the strong crossflow but redirects the coolant in the lateral direction that eventually contributes to the formation of a counterrotating vortex pair in the streamwise direction and thus augments local heat transfer and improves overall cooling effectiveness. Pressure drop measurement showed that the full-length triangular pin fin has a higher-pressure loss but the partial-length pin fin can lower the pressure loss considerably without compromising additional cooling performance.

Control of sound transmission into a hybrid double-wall sandwich cylindrical shell

A 3D analytical model is formulated for diffuse sound field transmission control through a smart hybrid double concentric sandwich circular cylindrical shell structure in presence of external and internal air gap mean flows. The multi-input multi-output sliding mode control is applied to enhance the sound transmission loss characteristics via direct control action of a uniform force piezoelectric actuator layer along with semi-active variation of the stiffness/damping characteristics of the electrorheological fluid core layer incorporated in a non-collocated configuration within the external or internal shell structure. Extensive numerical simulations examine the uncontrolled/controlled diffuse field sound transmission loss spectrums in a broad frequency range for single-wall and hybrid double-wall sandwich shells at selected external and air gap Mach numbers. The proposed smart hybrid active/semi-active double-wall configuration is demonstrated to provide satisfactory overall acoustic insulation control performance with much lower operative energy requirements. Limiting cases are considered, and validity of the formulation is verified against the available data.

Numerical simulation of broken pin effects on the flow field and cooling performance of a double-wall cooling configuration

In this paper, the flow characteristics of the double wall structure are presented and the effect of the broken pin size on the cooling performance and flow field of the double wall configuration is investigated. A periodic plate model with seven units is adopted, and there are an impingement hole and a film hole in each unit. Under five blowing ratios, six different sizes of the broken pin are compared, and the double wall configuration without broken pins is taken as the baseline. The results show that if the broken pins height is too small, the cooling effectiveness usually cannot be improved. With the presence of broken pins with a height of more than 0.4, the effectiveness is improved due to the enhancement of reattachment and recirculation of coolant. With the increase of the broken pin height, the cooling effectiveness increases. However, the increase of the diameter does not always improve the cooling performance, since the limiting effect of the wall jet. In this study, Case 6 with the largest broken pin always has the best cooling performance, but also the largest flow resistance. In Case 6 temperature is reduced by almost 15 K compared to the baseline, and more areas have relatively higher cooling effectiveness.

Vortex Structure Effects on Impingement, Effusion, and Cross Flow Cooling of a Double Wall Configuration

A variety of different types of vortices and vortex structures have important influences on thermal protection, heat transfer augmentation, and cooling performance of impingement cooling, effusion cooling, and cross flow cooling. Of particular interest are horseshoe vortices, which form around the upstream portions of effusion coolant concentrations just after they exit individual holes, hairpin vortices, which develop nearby and adjacent to effusion coolant trajectories, and Kelvin-Helmholtz vortices which form within the shear layers that form around each impingement cooling jet. The influences of these different vortex structures are described as they affect and alter the thermal performance of effusion cooling, impingement cooling, and cross flow cooling, as applied to a double wall configuration.

Internal and external cooling of a full coverage effusion cooling plate: Effects of double wall configuration and conditions

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal boundary conditions, after mainstream flow conditions are established. For the effusion cooled surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). For the coolant side, presented are spatially-resolved distributions of surface Nusselt numbers (measured using liquid crystal thermography). Of interest are the effects of streamwise development, blowing ratio, and Reynolds number. Streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) on the effusion plate are 15 and 4, respectively. Effusion hole diameter is 6.35 mm, effusion hole angle is 25°, and effusion plate thickness is 3 hole diameters. Considered are overall effusion blowing ratios from 2.9 to 7.5, with subsonic, incompressible flow, and constant freestream velocity with streamwise development, for two different mainstream Reynolds numbers. For the hot side (mainstream) of the effusion film cooling test plate, results for two mainflow Reynolds numbers of about 145000 and 96000 show that the adiabatic cooling effectiveness is generally higher for the lower Reynolds number for a particular streamwise location and blowing ratio. The heat transfer coefficient is generally higher for the low Reynolds number flow. This is due to altered supply passage flow behavior, which causes a reduction in coolant lift-off of the film from the surface as coolant momentum, relative to mainstream momentum, decreases. For the coolant side of the effusion test plate, Nusselt numbers generally increase with blowing ratio, when compared at a particular streamwise location and mainflow Reynolds number.

Heat transfer characteristics of high crossflow impingement channels: Effect of number of holes

In modern turbine airfoils, narrow impingement cooling channels can be formed in a double-wall configuration. In these wall-integrated cooling cavities, the generated crossflow is one of the most important design factors, and hence, the number of impingement holes included in a channel. This study examines experimentally the influence of the number of impingement holes on the heat transfer characteristics of narrow impingement channels. The channels consist of two rows of jets where the number of holes in the axial direction is varied from 5 to 10, maintaining the same jet plate open area. Local heat transfer coefficient distributions are obtained for all channel interior walls using the transient liquid crystal technique and over a range of Reynolds numbers (20,300–41,500). The results show an important heat transfer degradation at higher open areas and a small influence of the number of holes at upstream channel positions.

Effect of Varying Jet Diameter on the Heat Transfer Distributions of Narrow Impingement Channels

The development of integrally cast turbine airfoils allows the production of narrow impingement channels in a double-wall configuration, where the coolant is practically injected within the wall of the airfoil providing increased heat transfer capabilities. This study examines the cooling performance of narrow impingement channels with varying jet diameters using a single exit design in an attempt to regulate the generated crossflow. The channel consists of a single row of five inline jets tested at two different channel heights and over a range of engine representative Reynolds numbers. Detailed heat transfer coefficient distributions are evaluated over the complete interior surfaces of the channel using the transient liquid crystal technique. Additionally, local jet discharge coefficients are determined by probe traversing measurements for each individual jet. A 10%-increasing and a 10%-decreasing jet diameter pattern are compared with a baseline geometry of uniform jet size distribution, indicating a considerable effect of varying jet diameter on the heat transfer level and the development of the generated crossflow.

Detailed Heat Transfer Distributions of Narrow Impingement Channels for Cast-In Turbine Airfoils

The current capabilities of the foundry industry allow the production of integrally cast turbine airfoils. Impingement cooling effectiveness can be then further increased due to the manufacturing feasibility of narrow impingement cavities in a double-wall configuration. This study examines experimentally, using the transient liquid crystal technique, the cooling performance of narrow cavities consisting of a single row of five impingement holes. Heat transfer coefficient distributions are obtained for all channel interior surfaces over a range of engine realistic Reynolds numbers varying between 10,900 and 85,900. Effects of streamwise jet-to-jet spacing (X/D), channel width (Y/D), jet-to-target plate distance (Z/D), and jet offset position (Δy∕D) from the channel centerline are investigated composing a test matrix of 22 different geometries. Additionally, the target plate and sidewalls heat transfer rates are successfully correlated within the experimental uncertainties providing an empirical heat transfer model for narrow impingement channels. The results indicate similarities with multijet impingement configurations; however, the achievable heat transfer level is about 20% lower compared to periodic multijet impingement correlations found in open literature.

Preparation of near micrometer-sized TiO2 nanotube arrays by high voltage anodization

Highly ordered TiO2 nanotube arrays with large diameter of 680–750nm have been prepared by high voltage anodization in an electrolyte containing ethylene glycol at room temperature. To effectively suppress dielectric breakdown due to high voltage, pre-anodized TiO2 film was formed prior to the main anodizing process. Vertically aligned, large sized TiO2 nanotubes with double-wall structure have been demonstrated by SEM in detail under various anodizing voltages up to 225V. The interface between the inner and outer walls in the double-wall configuration is porous. Surface topography of the large diameter TiO2 nanotube array is substantially improved and effective control of the growth of large diameter TiO2 nanotube array is achieved. Interestingly, the hemispherical barrier layer located at the bottom of TiO2 nanotubes formed in this work has crinkles analogous to the morphology of the brain cortex. These structures are potentially useful for orthopedic implants, storage of biological agents for controlled release, and solar cell applications.

A simple method to optimize the sound package in a double wall structure.

The acoustic contributions to the transmission loss of an unbounded sound package in a double panel structure are investigated. For this purpose, a simple analytic expression of the normal incidence sound transmission loss of the double panel structure is proposed in terms of three main contributions: sound transmission loss of the panels, sound transmission loss of the blanket, and sound absorption due to multiple reflections inside the structure. It is shown that (i) at high frequencies, the transmission loss contribution of the blanket is preponderant compared to the absorption contributions;(ii) at the cavity resonance frequencies, the absorption contribution allows to attenuate the dips of insulation; and (iii) at medium and low frequencies, when the absorption performance of the porous layer is poor, the absorption contributions in the air‐gaps can decrease the sound transmission loss performance of the double panel. The proposed methodology can also be used to estimate, from classical impedance tube measurements of the sound package only, the transmission loss of the whole double wall configuration. Testing the influence of various sound packages in a given double panel structure thus becomes quick and much less expensive compared to classical tests.

Investigation of airborne versus structure-borne insertion loss of acoustic materials attached to a flat panel.

This paper discusses methods to predict airborne and structure-borne insertion loss of acoustic materials (fiber, foams, etc.) in single wall and double wall configurations attached to various structures. Specifically, a transfer matrix method based approach is proposed and compared to finite element and statistical energy analysis based predictions. Based on several numerical and experimental results, it is shown first that this method presents a simple and general model that can handle easily and automatically practical configurations. Next, a systematic comparison of structure-borne versus airborne excitation is presented for various structures and sound packages. In particular, the effect of damping and nature of coupling between the sound package and the main structure is discussed.

Measurement of SEA damping loss factor for complex structures

Statistical Energy Analysis has become extremely popular in the transportation industry. As a prediction tool, it offers appealing advantages such as its wide frequency range and short computational time, which conventional methods do not offer. Critical parameter in every SEA model, the damping characteristics of the subsystems must be determined by way of experimentations. A variety of different techniques of measuring the damping loss factor were developed. These techniques can be divided into three main groups: (i) method based on the identification of modal damping by curve-fitting frequency response function, (ii) decay techniques based on-determination of the reverberation time and, (iii) steady-state techniques involving measurements of power input method much closely related to the definition of SEA since its starting point is the power balance. This work presents an experimental study of these techniques for various structures such as flat metallic panels, aircraft side walls (ribbed curved panels) and sandwich-composite panels in both low and high damping configurations (additions of damping materials, sound packages in both single wall and double wall configurations, mounting effects, ...). In particular, a critical discussion is made on the implementation, advantages and drawbacks of each method regarding its use in SEA modeling of complex structures.