Laser-Powder Bed Fusion (L-PBF) is an additive manufacturing technique used to melt metal material into solid three-dimensional parts. While offering a high degree of design freedom, L-PBF still has technical restrictions, like the achievable surface roughness, resolution and the need for support structures in overhanging areas. [1] Currently, L-PBF is used mainly to produce small batches of parts and prototypes. [2] In order to fully industrialize the technology, the research campus in Aachen is investigating possible future applications in turbomachinery while developing the corresponding processes with industry partners. Sealing systems, like honeycomb seal strips in gas turbines often require time-consuming joining and assembly operations that can be avoided by building up the structure monolithically using L-PBF. The following process development study proves the feasibility of manufacturing honeycombs with L-PBF using the Nickel-based super-alloy Inconel 718 (IN718) on an EOS M290 machine. Here, we have evaluated the economic aspects of different build orientations of the seal strips. Afterwards, we conducted a systematic parameter study with continuous and pulsed wave laser emission and investigated the resulting wall thicknesses. A reduction in wall thickness of about 30% can be observed when a modulated laser is used.

Last stages of steam turbines and heavy-duty power gas turbines contribute significantly to output power and efficiency of whole turbine. Moreover, radial distribution of parameters downstream of the last stage provides boundary conditions for diffuser design. Thus, the increase of the last stage efficiency and obtainment of favorable radial distribution downstream of the last rotor blade is very important. Due to the long blades of last stages, resonance might occur. To avoid dangerous frequencies a damping wire or damping bolts are used. Such damping elements result in additional losses, so to minimize these losses a damping shroud is used instead. In general, the full damping shroud has to provide both the aerodynamic loss reduction and the resonance frequency offset. However, in most cases due to mechanical integrity limits instead of the full shroud a partial shroud is used. In this case the loss reduction feature of the partial shroud is diminished as compared with the full shroud. Sometimes, the use of the partial shroud results in the decrease of the efficiency compared with a stage with unshrouded rotor blades at small tip clearances. In this paper, a numerical investigation of the flow structure around full and partial shrouds with various geometries as well as the effect of the various shroud geometries on the turbine stage efficiency is carried out. Eight geometries with different number of fins of various heights are studied. Moreover, stage efficiencies for both shrouded and unshrouded blade are compared. Based on this comparison, reasonable design recommendations aimed to reduce the losses within the radial gap over the shroud are developed. In particular, filling the space in the gap with the additional honeycombs is considered and the effect on the flow structure and the last stage efficiency investigated. Numerical results obtained in the paper correspond well to the published test data.

The honeycomb seal shows promising characteristics in many turbine machines for the leakage control and rotor stability enhancement. However, the cost of honeycomb seal is relative high due to its complexities in manufacture and installation process. The hole-pattern seal has a very close leakage and rotordynamic performance with honeycomb seal, and also the manufacture and installation of hole-pattern seal are easier than the honeycomb seal, which attract the researchers and designers in recent years. In the published literature, there have been many papers dealt with the rotordynamic coefficients measurements, but very few researchers concentrated on the leakage control performance for the labyrinth seal with hole-pattern land. In this paper, the experimental tests were carried out to obtain the leakage rates versus pressure ratios at four clearances for the straight-through labyrinth seal with smooth stator, straight-through labyrinth seal with hole-pattern stator, stepped labyrinth seal with smooth stator and the stepped labyrinth seal with hole-pattern stator. The flow fields in the seal chambers were also visualized at different clearances and pressure ratios. Moreover, the CFD tool was also implemented to predict the leakage performance in labyrinth seals, and the numerical results were compared with the measurements. The results show that, the stepped labyrinth seal with hole-pattern land performs better leakage control characteristic than the straight-through labyrinth seal with hole-pattern land, and the stepped labyrinth seal with smooth land performs better leakage control than the straight through labyrinth seal with smooth land. For the stepped labyrinth seal, holes in the stator increase the effective clearance thus increase the leakage rate in seal. However, the straight-through labyrinth seal with hole-pattern land almost has the identical leakage performance with the smooth configuration.

Labyrinth seal designs for reduced leakage have been analyzed by three-dimensional CFD simulations. The objective is to learn the effect of seal geometry modifications on total leakage through the seal and arrive at an advanced seal setting for improved seal effectiveness through reduction in leakage. Numerical modeling of the flow field were conducted at various operating conditions. The baseline seal model for this study is a conventional straight-through rotating four-tooth labyrinth seal and static honeycomb land having symmetrical hexagonal cells. The tooth design configurations include stepped single & double notched straight and inclined teeth. Another objective is to learn the effect of staggered honeycomb land with respect to rotor/teeth rotation. The effect of teeth inclination & teeth rotation compared to stationary is also discussed. CFD results indicate improved seal effectiveness with staggered honeycomb cell land. The maximum improvement of ∼9% was observed with stepped and notched inclined teeth configuration when combined with staggered honeycomb land. The leakage reduction leading to improvement in seal effectiveness as compared to baseline configuration is largely due to higher flow resistance, higher turbulence and higher blockages by introducing vortex in leakage flow through step and cavities.

Gas turbine blades can be shrouded and designed with “knife edges” to reduce over tip leakages as an attempt to improve turbine stage efficiency. The smaller the tip gap is, the less the amount of leakage and consequently the higher the turbine efficiency. However a zero tip gap between the rotating blade and the stationary casing is simply not practical and not achievable for typical engine operations. One approach often consists of making the stationary shroud at the casing of abradable coating or of softer material in a honeycomb structure. In some cases, it is also common practice to pretrench the honeycomb structure to a certain height to reduce rubbing that could naturally occur with brand new hardware. This paper details the physical effects occurring between trenched and un-trenched configurations and quantifies the potential loss in turbine stage efficiency and power under such changes. Because front turbine stages are also cooled, this paper is also detailing the physical effects that are occurring between trenched and un-trenched configurations for a shrouded cooled turbine blade and the associated impact on performance. Since gas turbine are set to run at a specific gas mass flow, the differences between un-trenched and trenched for un-cooled and cooled are compared at the same given gas mass flow conditions. The paper concludes with key considerations for cooled turbine stage efficiency effects with and without trench.

In this paper, the effect of a novel honeycomb tip on suppressing tip leakage flow in a highly-loaded turbine cascade has been experimentally and numerically studied. The research focuses on the mechanisms of honeycomb tip on suppressing tip leakage flow and affecting the secondary flow in the cascade, as well as the influences of different clearance heights on leakage flow characteristics. In addition, two kinds of local honeycomb tip structures are pro-posed to explore the positive effect on suppressing leakage flow in simpler tip honeycomb structures. Based on the experimental and numerical results, the physical processes of tip leakage flow and its interaction with main flow are analyzed, the following conclusions can be obtained. Honeycomb tip rolls up a number of small vortices and radial jets in regular hexagonal honeycomb cavities, increasing the flow resistance in the clearance and reducing the velocity of leakage flow. As a result, the structure of honeycomb tip not only suppresses the leakage flow effectively, but also has positive effect on reducing the associated losses in cascade by reducing the strength of leakage vortex. Compare to the flat tip cascade at 1%H gap height, the relative leakage flow in honeycomb tip cascade reduces from 3.05% to 2.73%, and the loss at exit section is also decreased by 10.63%. With the increase of the gap height, the tip leakage flow and loss have variations of direct proportion with it, but their growth rates in the honeycomb tip cascade are smaller. Consider the abradable property of the honeycomb seal, a smaller gap height is allowed in the cascade with honeycomb tip, and that means honeycomb tip has better effect on suppressing leakage flow. Two various local honeycomb tip structures has also been discussed. It shows that local raised honeycomb tip has better suppressing leakage flow effect than honeycomb tip, while local concave honeycomb tip has no more effect than honeycomb tip. Compare to flat tip cascade, the leakage flow in honeycomb tip cascade, local concave tip cascade and local raised honeycomb tip cascade decrease by nearly 17.33%, 15.51% and 30.86% respectively, the losses at exit section is reduced by 13.38%, 12% and 28.17% respectively.

This article presents a parametric numerical study to analyze the sensitivity of wall heat fluxes on an academic acoustic liner to inlet conditions. Large Eddy Simulation (LES) is used to simulate an array of 20 aligned honeycomb cells on a flat plate with 10% porosity characteristic of installed liners. The computational domain is periodic in the span direction comprising 2 honeycomb cells. The operating conditions are representative of cruise with a Mach number of 0.5 at ambient pressure and temperature. Comparisons of heat fluxes obtained on a none perforated flat plate with the honeycomb liner are proposed with different inlet conditions: steady laminar boundary layer profile, turbulence injection and acoustic perturbation injection at different frequencies. Results show that for the operating condition and the boundary layer thickness used, large differences are observed on the first cells of the liners resulting from different transition to turbulence processes. A first important difference exists from laminar and turbulent conditions where turbulent conditions exhibits higher heat fluxes as expected. Then, case pulsed at the resonant frequency of the honeycomb shows higher heat fluxes than other frequencies. Finally, after a given number of cells, the heat fluxes reach an asymptotic behavior at the same level which seems to be controlled by the turbulence generated by the interaction of the flow and the perforations whatever the inlet conditions.

With the major aim of gathering information on the machine lateral stability in high pressure-high density conditions, and of assessing the prediction capabilities of the in-house design tools and overall process, a back-to-back centrifugal compressor has been instrumented and tested in several operating conditions. The present paper focuses on the secondary flows across the interphase balance drum of the back-to-back compressor, where the sealing is accomplished with a honeycomb seal. The compressor interphase section has been instrumented with dedicated special probes for the clearance measurement associated to pressure and flow angle probes in order to characterize pressure distributions and swirl variations depending on the specific operating range. The experimental data acquired over the machine operation have been compared with a three-dimensional steady-state numerical analysis results obtained from the simulation, carried out with a Reynolds averaged Navier-Stokes (RANS) approach, of the flowfield in the complex interphase secondary system composed by the impeller cavities and the honeycomb seal. This paper addresses the comparison between numerical results and experimental data, which allowed the matching of models with experiments in terms of pressure distribution and the complex flowfield. Finally, all the data have been used to validate an in-house one-dimensional flow network solver for pressure distribution and leakage flow calculations along cavities and seals. Results have shown a general good agreement between measured data and calculation output. In particular, computational fluid dynamic analysis provided detailed pressure and velocity distributions that allowed gaining insight in the physics of such a complex region. The one-dimensional model has been demonstrated to be a fast and reliable tool to well predict local pressure variations inside cavities and seals and, consequently, the residual axial thrust.

Labyrinth seals are used in many key sealing locations in gas turbines to control various leakage flows, e.g., to control the secondary air-flow from the compressor (bypassing the combustor), the turbine inter-stage leakages and blade tip leakages. This study was performed to assess the improvement in the performance of a labyrinth seal by using an air-curtain (cross-flow jet(s)) from the stator. Detailed parametric studies were performed to study the effect of the air-curtain jet pressure, location, and the number of jets on the seal performance with respect to the leakage flow. The analysis was done using 2-dimensional axisymmetric CFD simulations. It was found that in the case of a labyrinth seal with a flat stator (without a honeycomb attached to the stator) the air-curtain design can reduce the seal leakage by about 30% over the baseline seal design without air-curtains. This reduction happened because the air-curtain jet deflected the main seal jet away from the seal clearance. A similar conclusion was also obtained in case of a labyrinth seal with a honeycombed stator. Furthermore, our parametric studies with different air-curtain designs parameters implemented over a honeycombed labyrinth seal showed that the air-curtain jet pressure, location, and the number of jets were crucial factors governing the seal leakage. Amongst the air-curtain designs studied, it was found that implementing three air-curtains in the 1 st pocket gave the maximum leakage reduction (by about 50%) over the baseline design.

Improvements in turbine performance are increasingly driven by the need to control leakage both in the main gas path as well as in the secondary air flow system. Seals for static to static interfaces have a wide usage in gas turbine for component interface locations and are becoming more important as engines reach higher temperature targets and compressor pressure ratios. Both flex and honeycomb seals have been used for many years during other OEM seal service upgrades. These seals are designed to be capable of sustaining low leakage operation whilst achieving long lifetimes. To determine the sealing capability of honeycomb and flex seals an advanced hydraulically actuated rig was designed and constructed. A series of leakage performance tests were carried out that accurately simulate engine conditions, including pressure and relative axial and radial movements. The results of these tests are compared against previously presented data on standard membrane seals. Compared to the membrane seal, the flex seal has approximately 60% lower equivalent clearance when tested with uneven (triangular) grooves. This reduction was due to the bending of the seal and subsequent closing of the seal gap under pressure. The flex and membrane seal performed similarly well under more nominal conditions. The honeycomb seal achieved a consistently low leakage under all pressure loadings. All three sealing types have their place in the required technology mix which is essential when aiming for maximized engine performance and lifetime.

The aim of this study was to identify the best structures of the honeycomb (or structures used instead of it) that can be applied to a seal cavity labyrinth in order to improve the sealing performance. The problem was investigated numerically using the ANSYS CFX commercial software. The paper presents geometrical data concerning the proposed solutions to the labyrinth seal land structure. A simple straight-through labyrinth geometry with two leaned fins is analysed. Such a simple structure of the flow conditions was chosen to reduce the influence of other effects on the seal performance. Three-dimensional models of the labyrinth seal were elaborated for each honeycomb or honeycomb-like land structure. The following concepts were analysed: an inclination of the honeycomb cells, a land with different cell shapes (squeezed honeycomb) and honeycomb cells filled with a porous material. The labyrinth seals with different land structures were compared with two reference cases: a seal with a standard honeycomb land (with 1/8-inch cell size) and a seal with a smooth land. Calculations were performed for the pressure ratio values ranging from 1.08 to 1.8 and for varied sizes of the clearance. Main parameters of the leakage flows are discussed. Additionally, the influence of the inlet narrowing on the seal performance is investigated. A qualitative assessment of the seal concepts is made and the most promising solutions are pointed out.

A novel leakage flow control strategy with honeycomb seal applied on the tip of the rotor blades in a highly-loaded turbine cascade is proposed. The numerical method is used to study the tip leakage flow in a highly-loaded turbine cascades with flat tip and with honeycomb seal structure, the mechanism of honeycomb tip on inhibiting leakage flow is analyzed, the influence of various relative gap heights is also been investigated. The discussions of the action of the honeycomb-tip structure in reducing leakage flow and improving the turbine efficiency provide the according for control methods of tip leakage flow. Through the comparative study among three different tip structures of honeycomb tip, honeycomb casing and flat tip, the results show that both honeycomb tip and honeycomb casing inhibit the leakage flow effectively, but honeycomb tip has positive effect on reducing the flow loss in cascade. For the cascade with honeycomb tip, on one hand, the vortices rolled up in the regular hexagon honeycomb cavities dissipate the energy of the tip leakage flow, and the range of influence of the vortices is nearly one third of the tip clearance height. On the other hand, the radial jets caused by the honeycomb obstruct the tip leakage flow like a “pneumatic fence”, resulting in weaker leakage flow and less leakage flow rate. Besides, the honeycomb tip reduces the scale of the leakage vortex, thus the leakage loss also decreases. Compared with the flat tip cascade at the clearance height of 1%H, the honeycomb tip cascade with the same clearance height obtains decrease of the leakage flow rate and leakage flow speed in circumference by 10.16% and 20%. As a result, the leakage vortex in honeycomb tip cascade is undermined, the loss is reduced by nearly 4.43%. Considering the abradable property of the honeycomb seal that can protect the blade tips from damage, the cascade with honeycomb tip structure can obtain a smaller clearance height and achieve better sealing effect. Compared to cascade with the flat tip at the clearance height of 2%H, the amount of leakage flow using inlet flow in the honeycomb tip cascades decreases by 17.33%, 36.63% and 54.79% at the clearance heights of 2%H, 1.5%H and 1%H, the losses related to the leakage flow is reduced by nearly 5.71%, 14.33% and 25.24%, respectively.

Effect of leakage flow in honeycomb shroud seals on the aerodynamic performance of steam turbine stages in the high-pressure cylinder was numerically investigated by using the commercial CFD (Computational Fluid Dynamics) software ANSYS CFX11.0. The geometrical parameters of the honeycomb shroud seal, including the sealing clearance, cell depth and cell diameter, were selected as the research objectives to compute the aerodynamic performance of turbine stages at a wide range of dimensions. The numerical results show that the leakage rate in the shroud honeycomb seal is almost linearly increased with increase of sealing clearance. Correspondingly, the total-total isentropic efficiency of turbine stages decreases as well. As the cell depth increases, the total-total isentropic efficiency of the turbine stages is firstly increased and then almost kept constant, and the leakage rate in the honeycomb shroud seal is firstly decreased and then almost kept constant as well. For different honeycomb cell diameters, the leakage rate and stage efficiency are mainly determined by the flow structures in the honeycomb cells and seal outlet region. The present studies also show that, as the cell diameter increases, the total-total isentropic efficiency increases whereas the leakage rate decreases. Among the studied geometrical parameters (i.e. sealing clearance, cell depth and cell diameter), the variation of sealing clearance has a pronounced influence on the mixing loss in the main flow paths, but the variation of cell diameter has less effect on the aerodynamic performance of the turbine stages than that of sealing clearance. If the cell depth is not very small, the variation of cell-depth has a minor effect on the aerodynamic performance in the turbine stages.

The hole-pattern seal is usually used as a replacement of honeycomb seal due to their similarities in geometry and performance (leakage and rotordynamic). Compared with the honeycomb seal, the hole-pattern seal is easier to be manufactured and installed thus it is welcomed by the manufactures. However, most current literatures about the hole-pattern seal mainly addressed the rotordynamic characteristic of the shaft seal. Almost no research attempts to give an insight into the aerodynamic performance of the hole-pattern seal applied in turbine stages. Therefore, the main objective of the present paper is to investigate how the hole-pattern seal geometries, i.e. sealing clearance, hole-diameter and hole-depth, affect the aerodynamic performance of the steam turbine stages. With the commercial CFD (Computational Fluid Dynamics) software ANSYS CFX11.0, the leakage rates and aerodynamic efficiencies for the two stages with hole-pattern shroud seals were obtained and compared with those configured with honeycomb shroud seals at a range of seal dimensions. The results show that the leakage rate from the hole-pattern shroud seal is a bit higher than that from the honeycomb shroud seal at the same geometrical parameters (i.e. sealing clearance, hole/cell-diameter and hole/cell-depth). However, for these two configurations, the aerodynamic efficiencies are very close at the small sealing clearance cases. Big differences are shown at the large sealing clearance cases due to the difference in hole-area ratio. For the turbine stages with various hole-diameters and hole-depths, the aerodynamic performance of the turbine stages with honeycomb/hole-pattern seals are mainly affected by the flow patterns at the seal outlet if the sealing clearance is fixed. The sealing clearance has little effect on the flow pattern in the cells/holes, but it has a significant effect on the flow fields in the seal outlet chamber, thus affects the secondary flow development in the downstream flow paths.

Hole-pattern or honeycomb seals have been commonly used for many years in the Oil & Gas industry as damper seals for turbomachinery. The main motivation has been to introduce additional damping to improve the shaft rotordynamic stability operating under high pressure conditions. Experience has shown that the dynamic and even static characteristics of those seals are very sensitive to the operating clearance profile as well as the installation tolerances. Rotordynamic stability is related not only to the seal effective damping but to the effective stiffness as well. In fact, for this kind of seal, the effective stiffness can be high enough to alter the rotor system’s natural frequency. The seal stiffness is strictly related to the tapering contour: if the clearance profile changes from divergent to convergent, the effective stiffness may change from a strong negative to a strong positive magnitude, thus avoiding the rotor natural frequency drop as it is detrimental for the stability. Unfortunately the effective damping is reduced at the same time but this can be improved using proper devices to keep the pre-swirl low or even negative (e.g. swirl brakes, shunt holes). This paper presents the results from an extended test campaign performed in a high-speed rotor test rig equipped with active magnetic bearings working under high pressure (14krpm, 200bar gas inlet pressure), with the aim to validate the rotordynamic characteristics of a negative pre-swirl, convergent honeycomb seal and demonstrate its ability to effectively act as a gas bearing as well as a seal. The test plan included variations of inlet pressure, differential pressure (given the same inlet pressure) as well as rotational speed in order to fully validate the seal behaviour. This kind of test was performed in a “dynamic mode”, exciting the spinning test rotor through a pair of AMBs along linear orbits. Additionally the impact of the seal to rotor static eccentricity and the seal to rotor angular misalignment were both experimentally investigated and compared to relevant CFD simulations. This kind of test was performed in a “static mode”, imposing through the AMBs the required eccentricity / angular misalignment and then measuring the forces needed to keep the rotor in the original position. “Dynamic mode” test was also performed in order to check the impact of the seal static eccentricity on its dynamic behaviour. Finally the test results were compared with predictions from a state of the art bulk flow code in order to check the predictability level for future design applications.

This paper presents results from an extensive experimental study on the rubbing behavior of labyrinth seal fins and a honeycomb liner. The objective of the present work is to improve the understanding of the rub behavior of labyrinth seals by quantifying the effects and interactions of sliding speed, incursion rate, seal geometry and seal fin rub position on the honeycomb liner. In order to reduce the complexity of the friction system studied, this work focuses on the contact between a single seal fin and a single metal foil. The metal foil is positioned in parallel to the seal fin to represent contact between the seal fin and the honeycomb double foil section. A special test rig was set up enabling the radial incursion of a metal foil into a rotating labyrinth seal fin at a defined incursion rate of up to 0.65 mm/s and friction velocities up to 165 m/s. Contact forces, friction temperatures and wear were measured during or after the rub event. In total, 88 rub tests including several repetitions of each rub scenario have been conducted to obtain a solid data base. The results show that rub forces are mainly a function of the rub parameters incursion rate and friction velocity. Overall, the results demonstrate a strong interaction between contact forces, friction temperature and wear behavior of the rub system. The presented tests confirm basic qualitative observations regarding blade rubbing provided in literature.

The design of the newest aircraft propulsion systems is focused on environmental impact reduction. Extensive research is being carried out with the purpose of improving engine efficiency, enhancing crucial features, in order to decrease both fuel consumption and pollutant emissions. A lot of improvements to fulfill these objectives must be made, focusing on the optimization of the main engine parts through the utilization of new technologies. The leakage flow reduction in the turbo machinery rotor-stator interaction is one of the main topics to which numerous efforts are being devoted. Labyrinth seals, widely employed in the aerospace field thanks to their simple assembly process and maintenance, can be the means to achieve these objectives. This paper mainly focuses on the optimization of the labyrinth seal stator part, characterized, in modern Low Pressure Turbines (LPT), by a honeycomb cell pattern. The first phase of this study deals with the implementation and validation of a Computational Fluid Dynamics (CFD) numerical model, by using the experimental data available in the literature. Discharge coefficients obtained by numerical simulations, performed at different clearances and pressure ratios on both smooth and honeycomb non-rotating labyrinth seals, are presented and compared to the literature data. Then, for both convergent and divergent flow conditions, the effects on the discharge coefficient due to variations in several cell pattern parameters (i.e. cell diameter, depth and wall thickness) and fin tip thickness are shown. For these analyses the values of clearance and pressure ratio are set at a constant value.

A modification of a conventional straight four-tooth labyrinth seal with inclined teeth including single and double stepped notches is proposed. The variants are to be numerically modeled and evaluated for potential leakage reduction through the seal as a result of the developing flow field. The CFD methodology for numerical investigation is first validated by comparison with literature data from static labyrinth seal experiments. The objective is to numerically analyze the proposed “Notched Inclined Teeth” with solid and honeycomb lands and verify the leakages. Another objective is to compare these leakages with the “Stepped Double Notched Straight Tooth” variant discussed by the present authors in a previous paper. Results indicate that the proposed modifications — single and double stepped notched inclined teeth, systematically reduce the seal leakage compared to the baseline straight and forward inclined teeth due to higher turbulence, higher blockages by introducing vortex in leakage flow through step and cavities, and higher flow resistance as compared to baseline model.

A variety of techniques are available today that may be employed by the compressor designer to minimize the adverse effects of inlet distortion. The effects of individual stage rotor matching and blade chord length have been qualitatively indicated by isolated airfoil data. These effects have been verified through testing of several multistage axial flow compressors. Matching of early compressor stages well below their peak pressure ratio has been shown to significantly reduce the sensititivty of the entire compressor-to-inlet distortion. Careful selection of blade geometry by the designer may be used to provide a favorable balance between distortion tolerance and performance. In addition, increases in rotor blade chord length and use of honeycomb blade tip shrouds have been shown to further reduce the compressor’s sensititivity to distortion. Finally, the association of inlet distortion with turbulence is established. This association assures the designer that accommodations made for time-average spatial distortion will be effective in combating the adverse effects of inlet turbulence.

A technique is described for producing rectangular cell ceramic honeycomb regenerators for use in heat engines. Extrusion-embossing of cordierite-filled thermoplastic sheet is the method used to produce disks. Compositions, fabrication parameters, and fabrication procedures are included.