Perforated Liners Research Articles

Spectral analysis of the flow sound interaction at a bias flow liner

The interaction between the flow field and the sound field is responsible for the sound absorption at perforated acoustic liners with bias flow and has to be investigated contactlessly. Based on the optically measured flow velocity spectrum, an energy analysis was performed. As a result, the generation of broadband flow velocity fluctuations in the shear layer surrounding the bias flow caused by the flow sound interaction has been observed. In addition, the magnitude of this acoustically induced flow velocity oscillation exhibits a correlation with the acoustic dissipation coefficient of the bias flow liner. This supports the assumption that an energy transfer between the flow field and the sound field is responsible for the acoustic damping.

HEAT TRANSFER AND EXTERNAL QUALITY ATTRIBUTES OF 'REGAL SEEDLESS' TABLE GRAPES INSIDE MULTI LAYERED PACKAGING DURING POSTHARVEST COOLING AND STORAGE

Postharvest packaging of table grapes is characterized by multi-layer packaging comprising of the carton box, the inner liner film, the individual bunch carry-bag and the SO2 sheet. This multi-layered packaging is required to allow sufficient airflow to efficiently cool packed grapes in order to preserve quality. Total pressure drop and cooling rates of different table grape packaging systems were measured and the percentage contributions of each package component and the fruit bulk were determined. Also, the effects of different carton liners on the cooling rate and external quality attributes of table grapes were investigated. Fruit quality attributes measured included stem dehydration and browning, SO2 injury and decay. On average the liner films contributed significantly higher to total pressure drop (61.04±15.91 %) than other components of the package combinations. Compared with the cooling of bulk grape bunches, the presence of the bunch carry bag increased the half and seven-eighth cooling time by 61.1 % and 97.3 %, respectively. The addition of plastic liners over the bunch carry bag increased the half and seven-eighth cooling time by 168.9 % and 185.2 %, respectively. Non-perforated liners maintained relative humidity (RH) close to 100 % during cold storage and during a 7-day shelf-life period which resulted in delaying the loss of stem quality but significantly (P  0.05) while increasing the incidence of SO2 injury and berry drop during storage compared with perforated liners. INTRODUCTION In most fresh food refrigeration systems, heat is transferred primarily by forced convection, where cold air is forced through food packages; therefore, the temperature and its homogeneity is largely governed by the patterns of the airflow (Smale et al., 2006; Zou et al., 2006). Table grapes are non-climacteric fruit and therefore should be harvested when reaching optimum maturity (Ginsburg et al., 1978; Hardenburg et al., 1986). However, fruit quality tends to deteriorate rapidly during postharvest handling and storage, thus reducing shelf-life during marketing. Deterioration of table grape quality is mainly characterised by stem (rachis) dehydration and browning, fruit weight loss and colour change, accelerated berry softening, berry shatter and high incidence of berry decay due mainly to Botrytis cineria. Table grapes are packed in multi-layered packaging which includes the carton boxes with multiple inner-packaging materials including carton liner films, SO2 pads, moisture absorption sheets and bunch carry bags (Ngcobo et al., 2011). Resistance to airflow may even be higher during table grape cooling due to the fact that berry bunches are packed inside multi-layered packages. It is therefore important to understand the effects of packaging materials and produce on airflow in order to fully understand cooling patterns and moisture transfer properties for the design of efficient cooling systems. The aim of this experiment was to investigate the effects of multi-layered packaging on airflow and cooling patterns and on external quality attributes of table grapes during cooling and storage. MATERIALS AND METHODS

Ripening behavior and quality of modified atmosphere packed ‘Doyenne du Comice’ pears during cold storage and simulated transit

The effect of MAP on extending storage life and maintaining fruit quality was studied in ‘Doyenne du Comice’ (Pyrus communis L.) pears at Hood River and Medford, Oregon. Control fruit packed in standard perforated polyethylene liners started to show senescent core breakdown and lost the capacity to ripen at 20°C after 4–5 months of cold storage in Hood River and after 5.25–6 months in Medford. LifeSpan® L257 MAP achieved steady-state atmospheres of 15.8% O2+3.7% CO2 in Hood River and 15.7–17.5% O2+3.8–5.7% CO2 in Medford. MAP inhibited ethylene production, ascorbic acid degradation and malondialdehyde accumulation, and extended storage life for up to 6 months with maintenance of fruit flesh firmness (FF) and skin color without commercially unacceptable level of physiological disorders. After 4, 5 and 6 months at −1°C, MAP fruit exhibited climacteric-like patterns of ethylene production and softened to proper texture with desirable eating quality on day 5 during ripening at 20°C. After 6 months at −1°C plus 2 weeks of simulated transit conditions, MAP fruit maintained FF and skin color and had good eating quality at transit temperatures of 2 and 4.5°C (10.1–11.5% O2+4.8–5.2% CO2), but reduced FF substantially and developed internal browning disorder at 7.5 and 20°C (3.2–7.2% O2+7.9–9.5% CO2). The storage life of ‘Doyenne du Comice’ pears with high eating quality could be increased by up to 2 months when packed in MAP as compared with fruit packed in standard perforated polyethylene liners.

Effect of Perforated Plates on the Acoustics of Annular Combustors

This paper aims to show the influence of perforated plates on the acoustic modes in aeronautical gas turbine combustion chambers. The analytical model was implemented in a three-dimensional acoustic Helmholtz solver to account for the effect of perforated plates. First, an analytic test case is used to validate the coding in the acoustic solver. Then, a computation of the acoustic modes in an actual industrial chamber is conducted, taking into account the perforated liners. For both cases, a study of the influence of the bias flow speed is conducted. The acoustic energy budget is also used to evaluate the respective contributions of the perforated plates. In the case of the industrial chamber, some plates are proved to be more effective than the others, depending on the mode structure.

Time-domain characterization of the acoustic damping of a perforated liner with bias flow

Combustion instabilities are caused by the interaction of unsteady heat releases and acoustic waves. To mitigate combustion instabilities, perforated liners, typically subjected to a low Mach number bias flow (a cooling flow through perforated holes), are fitted along the bounding walls of a combustor. They dissipate the acoustic waves by generating vorticity at the rims of perforated apertures. To investigate the absorption of plane waves by a perforated liner with bias flow, a time-domain numerical model of a cylindrical lined duct is developed. The liners' damping mechanism is characterized by using a time-domain "compliance." The development of such time-domain compliance is based on simplified or unsimplified Rayleigh conductivity. Numerical simulations of two different configurations of lined duct systems are performed by combining a 1D acoustic wave model with the compliance model. Comparison is then made between the results from the present models, and those from the experiment and the frequency-domain model of previous investigation [Eldredge and Dowling, J. Fluid Mech. 485, 307-335(2003)]. Good agreement is observed. This confirms that the present model can be used to simulate the propagation and dissipation of acoustic plane waves in a lined duct in real-time.

Investigating the Effects of Table Grape Package Components and Stacking on Airflow, Heat and Mass Transfer Using 3-D CFD Modelling

The flow phenomenon during cooling and handling of packed table grapes was studied using a computational fluid dynamic (CFD) model and validated using experimental results. The effects of the packaging components (bunch carry bag and plastic liners) and box stacking on airflow, heat and mass transfer were analysed. The carton box was explicitly modelled, grape bunch with the carry bag was treated as a porous medium and perforated plastic liners were taken as a porous jump. Pressure loss coefficients of grape bunch with the carry bag and perforated plastic liners were determined using wind tunnel experiments. Compared with the cooling of bulk grape bunch, the presence of the carry bag increased the half and seven eighth cooling time by 61.09 and 97.34 %, respectively. The addition of plastic liners over the bunch carry bag increased the half and seven eighth cooling time by up to 168.90 and 185.22 %, respectively. Non-perforated liners were most effective in preventing moisture loss but also generated the highest condensation of water vapour inside the package. For perforated plastic liners, cooling with a high relative humidity (RH) air minimised fruit moisture loss. Partial cooling of the grape bunch inside the carry bag before covering it with a non-perforated plastic liner maintained the required high RH inside the package without condensation. The stacking of packages over the pallet affected the airflow pattern, the cooling rate and moisture transfer. There was a good agreement between measured and predicted results. The result demonstrated clearly the applicability of CFD models to determine optimum table grape packaging and cooling procedures.

The Use of Perforated Damping Liners in Aero Gas Turbine Combustion Systems

This paper considers the use of perforated porous liners for the absorption of acoustic energy within aero style gas turbine combustion systems. The overall combustion system pressure drop means that the porous liner (or “damping skin”) is typically combined with a metering skin. This enables most of the mean pressure drop, across the flame tube, to occur across the metering skin with the porous liner being exposed to a much smaller pressure drop. In this way porous liners can potentially be designed to provide significant levels of acoustic damping, but other requirements (e.g., cooling, available space envelope, etc) must also be considered as part of this design process. A passive damper assembly was incorporated within an experimental isothermal facility that simulated an aero-engine style flame tube geometry. The damper was therefore exposed to the complex flow field present within an engine environment (e.g., swirling efflux from a fuel injector, coolant film passing across the damper surface, etc.). In addition, plane acoustic waves were generated using loudspeakers so that the flow field was subjected to unsteady pressure fluctuations. This enabled the performance of the damper, in terms of its ability to absorb acoustic energy, to be evaluated. To complement the experimental investigation a simplified one-dimensional (1D) analytical model was also developed and validated against the experimental results. In this way not only was the performance of the acoustic damper evaluated, but also the fundamental processes responsible for this measured performance could be identified. Furthermore, the validated analytical model also enabled a wide range of damping geometry to be assessed for a range of operating conditions. In this way damper geometry can be optimized (e.g., for a given space envelope) while the onset of nonlinear absorption (and hence the potential to ingest hot gas) can also be identified.

Controlled Use of Downhole Calcium Carbonate Scaling for Sand Control: Laboratory and Field Results on Gullfaks

Summary Gullfaks has been in production since 1986 and produces approximately 11 500 std m3/d of oil from three Condeep platforms. The average water cut is approximately 75 to 80% and gas/oil ratio (GOR) is approximately 200 std m3/std m3. It has been estimated that between 50 and 100 t of sand is produced yearly per platform, with approximately 60 to 70% of the wells in active production (approximately 90) limited by sand production. The typical well completion is cased hole with selective production through perforated liners. Rock-mechanics studies have shown that sand will be produced irrespective of well inclination and perforation design. On Gullfaks, the sand-management strategy used has been to produce wells at "maximum" or "acceptable" sand rates. This strategy has led to significant gains in production, although there are challenges with this approach that include choke erosion, sand removal from the separators, and oil-in-water quality associated with discharge to sea. In response to this, Statoil has investigated different methods of retaining sand downhole by chemical sand consolidation, of which in-situ calcium carbonate (CaCO3) precipitation will form the basis for this paper. This technology involves squeezing into the near-wellbore formation predefined concentrations of urea and calcium nitrate along with the enzyme urease. After application, the well is shut in, during which the enzyme catalyzes the decomposition of urea to bicarbonate that reacts with calcium to form calcium carbonate. This paper will provide details of the laboratory evaluation and, in particular, will focus on the field results from the first-ever application of this type. A low-risk candidate well was selected that had a short perforated interval (19 m) and produced 88 std m3/d oil with a water cut of 94%. Results of the operation design and planning, logistics examination, thorough risk evaluation, and post-operation results with lessons learned will be presented.

One-sided multi-port techniques for characterisation of in-duct samples with nonlinear acoustic properties

Single sided multi-port system identification techniques, using sinusoidal excitation, for studying nonlinear energy transfer to higher harmonics for samples only accessible from one side such as perforated liners used as wall treatment in aircraft engine ducts are presented. The starting point is the so called polyharmonic distortion theory used for studying microwave systems. Models of different level of complexity are developed and the system identification results are compared. Experimental results, including error analysis, for a perforate sample are presented. The use of these techniques for analysing nonlinear energy transfer to higher harmonics and to improve the understanding of the physical phenomena involved are illustrated.

Reconstruction of time-domain impedance boundary condition considering the incident intensity effect on perforated-plate acoustic liner

Based on impedance prediction methods for a perforated plate acoustic liner, time-domain impedance boundary conditions are en- hanced with consideration of incident intensity. The impedance coefficient of the time-domain boundary condition is re-derived using parameters of the liner structure, and is classified by physical characteristics. To show the capability of the reconstructed impedance boundary condition, two numerical calculations are performed with comparison to analytical results. The first considers the one- dimensional wave propagation problem to account for the reflection wave due to an incident intensity variation on the acoustic liner. The second considers the excess attenuation of impedance surface. The numerical simulation is performed using the linearized Euler equa- tions (LEEs). Dispersion-relation-preserving finite difference scheme and optimized Adams-Bashforth time-integration method are used spatial discretization / time integration, respectively. The numerical results show excellent agreement with analytical results. Moreover, a reconstruction method of impedance boundary condition can easily obtain the impedance coefficients under environments of variant magnitudes of incident waves.

NUMERICAL INVESTIGATION OF THE ACOUSTIC DAMPING OF PLANE ACOUSTIC WAVES BY PERFORATED LINERS WITH BIAS FLOW

Perforated liners are extensively used in aero-engines and gas turbine combustors to suppress combustion instabilities. These liners, typically subjected to a low Mach number bias flow (a cooling flow through perforated holes), are fitted along the bounding walls of a combustor to convert acoustic energy into flow energy by generating vorticity at the rims of the perforated apertures. To investigate the acoustic damping of such liners with bias flow on plane acoustic waves, a time-domain numerical model is developed to compute acoustic wave propagation in a cylindrical duct with a single-layer liner attached. The damping mechanism of the liner is characterized in real-time by using a 'compliance', developed especially for this work. It is a rational function representation of the frequency-domain homogeneous compliance adapted from the Rayleigh conductivity of a single aperture with mean bias flow in the z-domain. The liner 'compliance' model is then incorporated into partial differential equations of the duct system, which are solved by using the method of lines. The numerical results are then evaluated by comparing with the numerical results of Eldredge and Dowling's frequency-domain model. Good agreement is observed. This confirms that the model and the approach developed are suitable for real-time characterizing the acoustic damping of perforated liners.

Effects of Packaging Liners on Cooling Rate and Quality Attributes of Table Grape (cv. Regal Seedless)

Table grapes are commonly packed in multi‐layered packages consisting of cardboard carton, plastic liners and carry bag/pouch to maintain product quality along the cold chain. Each liner is characterized by the number and the size of perforations, which influence the environmental conditions around the produce inside the package. This study investigated the effects of different carton liners on the cooling rate and quality attributes of ‘Regal Seedless’ table grapes. Fruit quality attributes measured include weight loss, stem dehydration and browning, SO2 injury, decay, berry firmness and colour. Non‐perforated liners maintained relative humidity (RH) close to 100% during cold storage and during a 7 day shelf life period, which resulted in delaying the loss of stem quality but significantly (p ≤ 0.05) increasing the incidence of SO2 injury and berry drop during storage, as compared with perforated liners. Perforated liners improved fruit cooling rates but significantly (p ≤ 0.05) reduced RH. Low RH in perforated liners resulted in significant (p ≤ 0.05) increase in stem dehydration and browning as compared with non‐perforated liners. Berry firmness decreased by 78% after 42 days of storage at −0.5°C. Significant (p ≤ 0.05) differences in berry firmness between the different packages were observed only during the first 7 days of storage. Berry colour changed from greenish‐yellow to yellowish‐green in all types of plastic liner during the storage period. Fruit decay occurred in all packages after a 7 day shelf life, with the highest incidence of decay occurring in liners with less perforation. Copyright © 2011 John Wiley & Sons, Ltd.

Tuned Passive Control of Acoustic Damping of Perforated Liners

To suppress combustion instabilities, perforated liners can be fitted along the bounding walls of a combustor to provide acoustic damping. These liners are typically subjected to a low-Mach-number bias flow (a cooling flow through perforated holes), and they tend to be effective only over narrow frequency ranges. To investigate the damping effect of perforated liners on plane acoustic waves and to increase their effective frequency range, experiments and numerical simulations are carried out. An acoustically driven pipe system containing a lined section was designed and experimentally tested. length of the pipe system, along with the bias flow rate, could be varied. experimental results showed that the liner damping depended on both the pipe length and the bias flow rate, in agreement with predictions from the numerical model presented by (Eldredge, J. D., and Dowling, A. P., The Absorption of Axial Acoustic Waves by a Perforated Liner with Bias Flow, Journal of Fluid Mechanics, Vol. 485, No. , 2003, pp. 307-335.). To maintain the acoustic damping of the liner in the presence of large frequency changes (corresponding to instability frequency changes in a combustor), real-time tuning of perforated liners was experimentally investigated. Both a pipe length parameter and the bias flow rate were sequentially tuned using a multiple-parameter tuning scheme. scheme required two algorithms to be developed: one for characterizing the finer's acoustic damping in real time and another for sequentially determining the two optimum actuation signals for the damper tuning. former involved developing a real-time version of the two-microphone technique for resolving the two plane acoustic wave strengths, which is widely applicable. On implementing these algorithms in the pipe system, optimal damping of the liner was achieved and maintained over a broad frequency range.

A real-time plane-wave decomposition algorithm for characterizing perforated liners damping at multiple mode frequencies

Perforated liners with a narrow frequency range are widely used as acoustic dampers to stabilize combustion systems. When the frequency of unstable modes present in the combustion system is within the effective frequency range, the liners can efficiently dissipate acoustic waves. The fraction of the incident waves being absorbed (known as power absorption coefficient) is generally used to characterize the liners damping. To estimate it, plane waves either side of the liners need to be decomposed and characterized. For this, a real-time algorithm is developed. Emphasis is being placed on its ability to online decompose plane waves at multiple mode frequencies. The performance of the algorithm is evaluated first in a numerical model with two unstable modes. It is then experimentally implemented in an acoustically driven pipe system with a lined section attached. The acoustic damping of perforated liners is continuously characterized in real-time. Comparison is then made between the results from the algorithm and those from the short-time fast Fourier transform (FFT)-based techniques, which are typically used in industry. It was found that the real-time algorithm allows faster tracking of the liners damping, even when the forcing frequency was suddenly changed.

Excitation of a Zero Mass Flow Liner for Acoustic Damping

The zero mass flow liner concept is able to convert a perforated liner with minimal damping qualities into a very effective sound absorber. The damping improvement results from an additional acoustic excitation within the zero mass flow liner. This paper studies the damping performance of the zero mass flow liner while changing the parameters of this excitation. A strong dependency on the sound pressure level and frequency is revealed from the experiments. A mode structure with a distinct pressure pattern seems to be of minor importance. However, it is of great benefit to operate the actuator at its natural resonances. This leads to a very good damping performance at a comparatively low input power.

A Passive Method to Control Combustion Instabilities with Perforated Liner

The effectiveness of perforated liner with bias flow on the control of combustion instability is investigated. Combustion instabilities result from the coupling between acoustic waves and unsteady combustion heat release. Sometimes the phenomenon happens in afterburners of aeroengine and rocket engine, and it always causes damage to flame holders, liner sections and other engine components. Passive methods, such as perforated liner, are often used to suppress such instabilities in application. In this article, first, a burner testbed is built in order to study the characteristic of this phenomenon. The unstable frequencies and unstable area are investigated experimentally. Then an analytical model, based on “transfer element method”, is developed and the numerical results are compared with those from experiments. At last the perforated liner is applied to the burner to suppress the instabilities. The results show that the sound pressure can be greatly reduced by the perforated liner.

Interaction Between the Acoustic Pressure Fluctuations and the Unsteady Flow Field Through Circular Holes

Gas turbine combustion systems are prone to thermo-acoustic instabilities, and this is particularly the case for new low emission lean burn type systems. The presence of such instabilities is basically a function of the unsteady heat release within the system (i.e., both magnitude and phase) and the amount of damping. This paper is concerned with this latter process and the potential damping provided by perforated liners and other circular apertures found within gas turbine combustion systems. In particular, the paper outlines experimental measurements that characterize the flow field within the near field region of circular apertures when being subjected to incident acoustic pressure fluctuations. In this way the fundamental process by which acoustic energy is converted into kinetic energy of the velocity field can be investigated. Experimental results are presented for a single orifice located in an isothermal duct at ambient test conditions. Attached to the duct are two loudspeakers that provide pressure fluctuations incident onto the orifice. Unsteady pressure measurements enable the acoustic power absorbed by the orifice to be determined. This was undertaken for a range of excitation amplitudes and mean flows through the orifice. In this way regimes where both linear and nonlinear absorption occur along with the transition between these regimes can be investigated. The key to designing efficient passive dampers is to understand the interaction between the unsteady velocity field, generated at the orifice and the acoustic pressure fluctuations. Hence experimental techniques are also presented that enable such detailed measurements of the flow field to be made using particle image velocimetry. These measurements were obtained for conditions at which linear and nonlinear absorption was observed. Furthermore, proper orthogonal decomposition was used as a novel analysis technique for investigating the unsteady coherent structures responsible for the absorption of energy from the acoustic field.

Dissipative diesel engine exhaust muffler featuring sintered metal fiber as acoustical fill liner.

Conventional exhaust muffler design for diesel truck applications often involves a combination of dissipative and reactive elements in order to provide generally broadband sound attenuation for the purpose of suppressing engine exhaust noise during normal operation or engine braking (i.e., venting compressed air through the exhaust system). The reactive portions of the muffler are usually present to provide low‐frequency spectrum transmission loss that cannot readily be achieved with classical perforated‐n′‐packing dissipative design. However, unlike standard perforated metal liners that are used to separate the exhaust gas stream from the muffler’s surrounding volume of acoustically absorbent fill, liner materials such as micro‐perforate and sintered metal fiber (SMF) metals offer high porosity and high‐flow resistance that should improve low‐frequency dissipative sound absorption. This study contrasts the modeled insertion loss, transmission loss, and noise reduction performance of a dissipative‐only mu...

A method to predict geomechanical properties and model well stability in horizontal boreholes

Abstract A methodology is proposed to quickly assess the stability risk for horizontal wells drilled in coal seams. The first task involves the estimation of strength and deformation parameters of the coal by indirect methods, such as the use of core description to assign a Geological Strength Index (GSI). The second task involves the use of a finite element analysis called FLAC to investigate factors such as the depth of fluid penetration while drilling the horizontal well and the stability of the wellbore during simulated production. These two factors are important because coal fines generated by the drill bit action are carried by the drilling fluid into the cleat system of the coal, thereby plugging the permeability pathways, and causing formation damage. On the other hand, a wellbore that may become unstable during pressure drawdown would require a perforated or slotted production liner. In this study, the conditions of drilling and production necessary for a stable horizontal well drilled into a Mannville coal seam at 750–800 m in the central Alberta Plains, were studied. Modeling showed that the depth of fluid penetration would be at least 2.2 m if there is no filter cake formation while drilling underbalanced. Drilling fluid penetration would be minimal if a filter cake is formed under overbalanced conditions. Furthermore, FLAC analysis showed that drilling a smaller diameter hole (5 cm) would be preferable because this size results in a stable wellbore during production compared to the standard 15-cm diameter hole.

CONCEPTUAL FUEL CHANNEL DESIGNS FOR CANDU-SCWR

This paper presents two of the fuel channel designs being considered for the CANDU-SCWR, a pressure-tube type supercritical water cooled reactor. The first is an insulated pressure tube design. The pressure tube is thermally insulated from the hot coolant by a porous ceramic insulator. Each pressure tube is in direct contact with the moderator, which operates at an average temperature of about . The low temperature allows zirconium alloys to be used. A perforated metal liner protects the insulator from being damaged by the fuel bundles and erosion by the coolant. The coolant pressure is transmitted through the perforated metal liner and insulator and applied directly to the pressure tube. The second is a re-entrant design. The fuel channel consists of two concentric tubes, and a calandria tube that separates them from the moderator. The coolant enters between the annulus of the two concentric fuel channel tubes, then exits the fuel channel through the inner tube, where the fuel bundles reside. The outer tube bears the coolant pressure and its temperature will be the same as the coolant inlet temperature, . Advantages and disadvantages of these designs and the material requirements are discussed.