Large Fan Research Articles

Strength Assessment of Fan Blade with Different Materials

Weight reduction of turbofan engines is one of the main concerns of aero engine manufacturers in order to cut fuel burn. To achieve higher fuel efficiency, aero engine manufacturers develop turbofans with higher bypass ratio, which can only be achieved with larger (and heavier) fan sections. This makes weight reduction in fan components a major consideration and becomes a key driver for the use of composite materials in future engines. The objective of this project is to design, perform structural analysis and optimization of a Composite fan blade. Development of a fan blade is comparable to a future large aircraft engine fan blade. This thesis is about the structural analysis of a composite fan blade with a honeycomb sandwich construction with a polymer matrix composite and honeycomb Aluminium core compared with baseline solid basic fan blade made of titanium. The focus of this work is to design the sandwich composite blade with honeycomb core and conduct static and dynamic analysis.

An introduction to glaciated margins: the sedimentary and geophysical archive

Abstract A glaciated margin is a continental margin that has been occupied by a large ice mass, such that glacial processes and slope processes conspire to produce a thick sedimentary record. Ice masses take an active role in sculpting, redistributing and reorganizing the sediment that they erode on the continental shelf, and act as a supply route to large fan systems (e.g. trough mouth fans, submarine fans) on the continental slope and continental rise. To many researchers, the term ‘glaciated margin’ is synonymous with modern day areas fringing Antarctica and the Arctic shelf systems, yet the geological record contains ancient examples ranging in age from Precambrian to Cenozoic. In the pre-Pleistocene record, there is a tendency for the configuration of the tectonic plates to become increasingly obscure with age. For instance, in the Neoproterozoic record, not everyone agrees on the location of rift margins and some fundamental continental boundaries remain unclear. Given these issues, this introductory paper has two simple aims: (1) to provide a brief commentary of relevant Geological Society publications on glaciated margins, with the landmark papers highlighted and (2) to explain the contents of this volume.

A Secondary Fan-spine Magnetic Structure in Active Region 11897

Abstract Fan-spine is a special topology in solar atmosphere and is closely related to magnetic null point, as well as circular-ribbon flares, which can provide important information for understanding the intrinsic 3D nature of solar flares. However, the fine structure within the fan has rarely been investigated. In present paper, we investigate a secondary fan-spine (SFS) structure within the fan of a larger fan-spine topology. On 2013 November 18, this large fan-spine structure was traced out owing to the partial eruption of a filament, which caused a circular-ribbon flare in NOAA Active Region 11897. The extrapolated 3D magnetic fields and squashing factor Q maps depict distinctly this fan-spine topology, its surrounding quasi-separatrix layer (QSL) halo, and a smaller quasi-circular ribbon with high Q located in the center, which implies the existence of fine structure within the fan. The imaging observations, extrapolated 3D fields, and Q maps on November 17 show that there indeed exists an SFS surrounded by a QSL, which is enveloped by another QSL halo corresponding to the overlying larger dome-shaped fan. Moreover, the material flows caused by the null-point reconnection are also detected along this SFS. After checking the evolution of the underneath magnetic fields, we suggest that the continuous emergence of magnetic flux within the central parasitic region encompassed by the opposite-polarity fields results in the formation of the SFS under the large fan.

A comparative study of coupled and decoupled fan flutter prediction methods under variation of mass ratio and blade stiffness

Flutter is a long standing issue for fan blades of civil aero-engines and becomes of further concern for modern light-weight designs with increasing fan diameters to reach ultra-high bypass ratios. Accurate flutter prediction is therefore of prime consideration in the design process in order to avoid catastrophic blade failure in operation or expensive redesign iterations if spotted in ground or flight tests. The traditional energy method, which is based on the assumption of negligible aeroelastic coupling, has been used to great extend to predict flutter of turbomachinery components including aero-engine fan blades, and is today by far the most widely applied technique. The underlying assumption of fluid–structure decoupling, however, has to be questioned for large fan blades that are characterized by low mass ratios and low stiffness. Implications of the violation of the system decoupling assumption on the prediction capabilities of the energy method are important to understand for the fan designer in order to allow an informed decision on the flutter prediction tool to use. In this work a comprehensive comparative study is presented in which the energy method is contrasted to the predictions of a strongly coupled fluid–structure interaction method for varying values of mass ratio and blade stiffness of a transonic three-dimensional fan rotor. The strength of aeroelastic coupling is evaluated in terms of the aeroelastic frequency shift and its impact on the prediction accuracy of the energy method is investigated. The results show the capability of the energy method to accurately predict flutter for a wide range of mass ratio and stiffness configurations, but its prediction accuracy is reduced for combined low mass ratio and low stiffness blades. Mechanisms governing the aeroelastic frequency shift are explained to allow a better understanding of the effect and a method for its prediction based on results of a decoupled analysis is shown.

Temperature Selection in the Preheating of Blanks for the Stamping of Large Wide-Chord Fan Blades

A new approach to the stamping of large wide-chord compressor blades is considered. Analysis of the constraints on the preheating of the blanks permits practical recommendations regarding the preheating conditions.

Petrology Characters of Conglomerates in Baikouquan Formation, Mahu Sag, Junggar Basin

Mahu Sag, one of the most oil and gas bearing sags in Junggar basin, is in the northwestern margin of the basin. On gentle slope region of the sag, a serial of large scale coarse fan delta deposits were developed in Triassic Baikouquan Formation. In order to understand the petrology characters of conglomerates in Baikouquan Formation, based on lots of cores, grain size analysis, normal thin sections, casting thin sections, scanning electron photomicrographs, mineral composition identifications, clay mineral and bulk composition identifications of X-ray diffraction, were comparatively studied for Xiazijie and Huangyangquan fan-delta in Mahu Sag. Mineral composition of conglomerates is main tuff, while eurite, dacite, rhyolite, andesite and granite are common. However, more tuff and granite, less eurite and andesite in Xiazijie fan-delta, there is no rhyolite in Huangyangquan fan-delta. Kaolinization and chloritization of conglomerates are ubiquitous in the formation. The content of chlorite and kaolinite is higher in Xiazijie fan-delta, with lower illite-smectite and illite. There is less feldspar of clastic and more calcite of cement in Xiazijie fan-delta.

Quantifying spatial and architectural relationships from fluvial outcrops

Outcrop analogue studies allow detailed investigation of sandstone body geometry and architecture within fluvial systems. Characterization of these elements is fundamental to understanding and quantifying sandstone body connectivity within hydrocarbon reservoir models, and hence improving recovery from those reservoirs being modeled. This study utilized a laterally and vertically continuous terrestrial light detection and ranging (lidar) data set from the La Serrata section of the Oligocene–Miocene Huesca fluvial fan, in the Ebro Basin in Spain. This data set was used to create a high-resolution three-dimensional digital outcrop model of a 2 km2 cliff section representing the heterogeneity in the medial (midfan) portion of a large fluvial fan. Geostatistical information (i.e., sandstone body width and thickness) extracted from the models using quantitative analytical techniques, integrated with traditional sedimentary log data, allowed the calculation of probability density functions of 42 sandstone bodies from corrected (true) width measurements. These data show that sandstone bodies are up to 6 m thicker and 209 m wider than previous studies have estimated. Furthermore, an observed temporal trend of thickening and widening of sandstone bodies up section before a reduction in the uppermost portion provides evidence for possible avulsion events. These data, compared with previous studies of this and other fluvial systems, illustrate the efficacy of digital outcrop models as quantitative tools for accurate characterization of critical reservoir elements from outcrop analogues.

Postglacial alluvial fan dynamics in the Cordillera Oriental, Peru, and palaeoclimatic implications

AbstractAlluvial fans record climate-driven erosion and sediment-transport processes and allow reconstructing past environmental conditions. Here we investigate the sedimentation history of two alluvial fans located in formerly glaciated valleys of the Cordillera Oriental, Peru.10Be exposure ages from the fan surfaces and radiocarbon ages from the fan interiors constrain the final stages of fan formation. The10Be and14C ages cluster mainly between 13.3–9.3 ka and 11,500–9700 cal yr BP, respectively. Our age data set indicates that—after deglaciation—large amounts of fan sediment were deposited until ∼10 ka, when sedimentation rates declined rather abruptly. This pattern is supported by10Be erosion rates for the fan catchments, because under the assumption of constant erosion the time needed to erode the material stored in the fans significantly exceeds their age. Correlating our ages with regional climate records indicates that precipitation exerts the primary control on fan sedimentation. Two periods with elevated lake levels and increased precipitation between 18 and 14.5 ka and from 13 to 11.5 ka resulted in rapid deposition of large fan lobes. Subsequently, lower precipitation rates decreased erosion in the catchments and sediment delivery to the fans, which have remained largely inactive since ∼9.5 ka.

Performance Testing of an Axial Flow Fan Designed for Air-Cooled Heat Exchanger Applications

An axial flow fan developed in the previous study is tested in order to characterize its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary computational fluid dynamics (CFD) results obtained using an actuator disk model (ADM) as well as a periodic three dimensional model indicate that the fan meets the specified performance targets, with an expected total-to-static efficiency of 59.4% and a total-to-static pressure rise of 114.7 Pa at the operating point. Experimental tests are performed on the M-fan in order to determine its performance across a full range of flow rates. A range of fan configurations are tested in order to ascertain the effect of tip clearance, blade angle, and hub configuration on fan performance. Due to the lack of a suitable facility for testing a large diameter fan, a scaled 1.542 m diameter model is tested on the ISO 5801 type A fan test facility at Stellenbosch University. A Reynolds-averaged Navier–Stokes CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. The results of the CFD model will be validated using the experimental data obtained. Both the CFD results and the experimental data obtained are compared to the initial CFD results for the full scale fan, as obtained in the previous study, by means of fan scaling laws. Experimental data indicate that the M-fan does not meet the pressure requirement set out in the initial study at the design blade setting angle of 34 deg. Under these conditions, the M-fan attains a total-to-static pressure rise of 102.5 Pa and a total-to-static efficiency of 56.4%, running with a tip gap of 2 mm. Increasing the blade angle is shown to be a potential remedy, improving the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap, with larger tip gaps substantially reducing fan performance. The losses due to tip gap are also shown to be overestimated by the CFD simulations. Both experimental and numerically obtained results indicate lower fan total-to-static efficiencies than obtained in the initial CFD study. Results indicate that the M-fan is suited to its intended application, however, it should be operated with a smaller tip gap than initially recommended and a larger blade setting angle. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.

Environmental setting of the early irrigation in Oasisamerica: Paleopedological evidences from the alluvial palaeosols in la Playa/Sonoran Desert

Environmental conditions and human-landscape interaction during the onset of the irrigated agriculture in Oasisamerica are not clear yet. In la Playa site (Sonora, NW Mexico), the evidences of sedentary population, land cultivation, and water management developed after the end of Altithermal period (around 4500 yr BP) include more than 550 archaeological features including hundreds of human cremations and a net of buried artificial channels. These findings were closely associated with several palaeosol levels alternating with sediments within a large alluvial fan. We studied micromorphological features, physical characteristics (color, texture, rock magnetic properties), and composition of organic matter, from three profiles (Maravillas, Zanja, and Cuatro Suelos), to reconstruct pedogenesis and sedimentary environment of the palaeosol sequences. Additional paleoenvironmental information was extracted from pollen assemblages, extracted from the Cuatro Suelos profile. The results pointed to a long period of geomorphic and climatic stability in the early-middle Holocene marked by a well-developed red Cambisol. This period was followed by an unstable interval around 4.5 kyr BP marked by severe erosion of earlier soil profiles and sedimentation of different kind: channel, floodplain, and fluvio-eolian. Later synsedimentary Fluvisols were formed showing signs of predominantly arid pedogenesis, interrupted by occasional flooding; indicators of human impact were also encountered. We conclude that the shift to irrigated agriculture as the main subsistence activity occurred during the period of major climatic and geomorphic fluctuation and then irrigation developed further under dry environment with limited water resources during the Late Holocene.

Point cloud technology and 2D computational flow dynamic modeling for rapid hazards and disaster risk appraisal on Yellow Creek fan, Southern Alps of New Zealand

Glacial recession in Alpine Valleys uncorks low-altitude tributary valleys that spill trapped sediments in the sediment cascade, in turn generating sediment-related hazards and flood hazards. Within this complex, the present contribution investigates the transition zone between the tributary and the main valley at Fox Glacier, New Zealand, where glacier recession has allowed the development of large debris flow fans. As the valley is narrow and its geomorphology is rapidly evolving, 3D point cloud technologies based on aerial photogrammetry from UAV or ground and airborne laser technologies are essential to understand the geomorphology and generate boundary conditions to run hazard simulations such as debris flows. Using airborne structure from motion photogrammetry with ground control points collected by RTK-GNSS, we investigated (1) the geomorphology of the valley to understand its evolution and (2) the role of this recent evolution on the flood hazards at the Yellow Creek debris flow fan. The geomorphology of the Fox River valley is a typical U-shape valley with steep valley walls that command the valley by more than 1000 m. The valley walls are connected to the bottom of the valley by active sediment aprons and debris flow fans at the exit of the tributaries. The slopes present several topographic steps or noses on both the aprons and the debris flow fans. By comparison with the glacial recession, they can be related to past locations of the limits of the glacier. On Straight Creek fan, the ridges are perpendicular to the valley and divide the fan between an overgrown half downstream the Fox Valley and an upstream section thinner and smaller. This pattern was also created by the presence of the glacier that stopped the development of the fan on its right (upstream half) while developing the true left hand side of the fan. On the other side of the valley, the debris flow fan of Yellow Creek presents a series of deep trough that control water flows. Flood simulations show that these controls can be overcome and instead of being channeled in other sub-channels, the flow tends to spread on the true right (downstream) end of the fan as a sheet flow. In the 2014 state of the fan, the safest location was thus on the true left half of the fan towards the glacier. Such information is essential as tourists occupy the valley and walk towards the glacier the whole year.

Subsurface aquifer heterogeneities of Lower Triassic clastic sediments in central Germany

Abstract A combined study of facies and diagenesis variations was carried out with the aim to understand small-scale heterogeneities in porosity and permeability of sandstones within a 219 m completely cored Middle Buntsandstein succession from central Germany. The well Erfurt 1/12 (EF-FB 1/12) allows studying aquifer quality variations by taking 49 plug samples of fresh rock material for thin section analyses and petrophysical measurements. This potential Buntsandstein aquifer is composed of varying portions of sandstones, mudstones and sandstone-mudstone interlayers, which were deposited on a large terminal fan system and in a large playa-lake in the basin centre. A fluvial channel and a sandflat depositional environment can be distinguished. Both are composed of varying amounts of channel-, sandsheet- and floodplain sediments of mainly massive, cross-bedded, horizontally laminated and ripple cross-bedded sandstones. Best aquifer potential occurs in the horizontally laminated and cross-bedded sandstones within channels of the fluvial environment, and in the massive sandstones of channels in sandflat deposits. Aquifer quality does not decrease with increasing depth or stratigraphic position. Instead, it is controlled by grain size and diagenetic evolution. Four diagenesis types were distinguished: (1) cementation type (CT), (2) leaching type (LT), (3) illite type (IT) and (4) mixed type (MT). Best aquifer quality was found in the leaching type (LT) consisting of larger grain sizes (medium sand), which led to the formation of a large primary pore network. Our data suggest a strong relation of hydraulic parameters not only with different facies types, architectural elements and depositional environments, but particularly with compaction and cementation during burial, and dissolution by meteoric water during subsequent uplift history. Thereby, present horizons with good hydraulic properties relate to this complex interaction of sedimentary facies and diagenetic evolution, but are restricted to only very local areas with no relevance for basin-wide fluid flow in the subsurface.

Affordable Uncertainty Quantification for Industrial Problems: Application to Aero-Engine Fans

Uncertainty quantification (UQ) is an increasingly important area of research. As components and systems become more efficient and optimized, the impact of uncertain parameters is likely to become critical. It is fundamental to consider the impact of these uncertainties as early as possible during the design process, with the aim of producing more robust designs (less sensitive to the presence of uncertainties). The cost of UQ with high-fidelity simulations becomes therefore of fundamental importance. This work makes use of least-squares approximations in the context of appropriately selected polynomial chaos (PC) bases. An efficient technique based on QR column pivoting has been employed to reduce the number of evaluations required to construct the approximation, demonstrating the superiority of the method with respect to full-tensor quadrature (FTQ) and sparse-grid quadrature (SGQ). Orthonormal polynomials used for the PC expansion are calculated numerically based on the given uncertainty distribution, making the approach optimal for any type of input uncertainty. The approach is used to quantify the variability in the performance of two large bypass-ratio jet engine fans in the presence of shape uncertainty due to possible manufacturing processes. The impacts of shape uncertainty on the two geometries are compared, and sensitivities to the location of the blade shape variability are extracted. The mechanisms at the origin of the change in performance are analyzed in detail, as well as the differences between the two configurations.

Effect of two-phase flow on transmission characteristics of oil film between friction pair

PurposeThe purpose of this paper is to use the viscosity of fluid to transmit power known as the hydro-viscous drive (HVD) to research the effect of two-phase flow on transmission characteristics.Design/methodology/approachIn this paper, a 3D computational model of oil film between friction pair was built to study the transmission characteristics of a two-phase oil film, and the distribution contours of pressure and temperature of oil film were investigated using the computational fluid dynamics technology.FindingsThe finding of the paper suggests that the distribution law of pressure and temperature of two-phase oil film is almost linear along the radial direction. However, since the physical phenomena near the outlet of the oil film are entirely different, there exists fluctuation. Meanwhile, the volume fraction of air was obtained at different rotation speeds, and the maximum value is 10.55 percent. Compared to the single-phase oil film, the torque transferred by the oil film is not linear with the rotation speed, its value decreases gradually.Originality/valueThis paper’s conclusions are very important for the study of HVD and its applications, which provide a new idea to further study the mechanism of oil film transmission and its cavitation. The development of fluid viscous speed clutch is dedicated to a large industrial fan and water pump speed regulation and energy saving. With the successful application of the technology, it will have more wide applications in different fields, such as, in steel, water, petrochemical, power plant of slag pump and exhaust fan.

Influence of a large debris flow fan on the late Holocene evolution of Squamish River, southwest British Columbia, Canada

Cheekye Fan is a large paraglacial debris flow fan in southwest British Columbia. It owes its origin to the collapse of Mount Garibaldi, a volcano that erupted in contact with glacier ice near the ...

Determining the Contribution of Ventilation and Insulation of Broiler Breeding Houses in Production Performance Using Analytic Hierarchy Process (AHP)

ABSTRACT This study was conducted using Analytic Hierarchy Process (AHP) in order to rank broiler breeding farms in Zanjan province, Iran, regarding buildings, installations, and equipment to determine their effects on production factors. Data on 108 farms were collected using designed forms. This data was analyzed based on the effectiveness of each parameter in the production and management category according to experts’ opinion. The results indicated that ventilation systems (fans, inlets, and damper) as well as wall and roof insulation in poultry houses, constituted 66% of the technology coefficient. The stocking density increased through improvement of the mechanization coefficient. Most of these farms used longitudinal or tunnel ventilation and a combination of small and large fans. Roof insulation was mostly done using glass wool, and corrugated plastic while installing the heaters outside the poultry house. In these farms, the use of nipple drinkers and plate feeders was more prevalent. Moreover, the results showed that feed conversion and production indices have a significant correlation with mechanization coefficient so that farms with better mechanization coefficients had lower conversion ratio (p=0.04) and higher production indices (p=0.015). In general, the results indicated that ventilation and air inlet systems, as well as wall and roof building technologies have the greatest influence on the mechanization coefficient, while better mechanization coefficients translated into improvements in production efficiency and economic performance of poultry farms.

River-damming, late-Quaternary rockslides in the Ötz Valley region (Tyrol, Austria)

The Ötz Valley and adjacent regions in Tyrol (Austria) have been repeatedly affected by large rockslope failures following deglaciation. Six rockslides, each over 107 m3 in volume, were emplaced into the Ötz and Inn valleys, five of which formed persistent rockslide dams. Even though catastrophic rockslope failures are short-lived events (commonly minutes) they can have long-lasting impacts on the landscape. For example, large fans have built in the Ötz Valley and knickpoints persist at the former dam sites even though the Ötz River has eroded through the deposits during the past thousands of years; exact age-constraints of rockslide dam failure, however, are still scarce. Empirical, geomorphic stability indices from the literature successfully identified the least and the most stable dams of this group, whereas the rest remain inconclusive with some indices variably placing the dams in the stable, unstable, and uncertain categories. This shows (a) that further index calibrations and (b) better age constraints on dam formation and failure are needed, and (c) that the exact processes of dam failure are not always trivial to pinpoint for ancient (partially) breached dams. This study is a contribution towards better constraining the nature and landscape impact of dam formation following large rockslope failures.

New Evidence on the Relief of the Southern Underwater Slope in the South Baikal Basin

A high-resolution bathymetric survey of the entire underwater slope in South Baikal was carried out for the first time by means of the multibeam echosounder. New elements were revealed in the underwater relief of the southern slope of the basin from the Kultuchnaya river to the Mysovka river, and a relevant regionalization was carried out into three areas according to the presence of ancient landforms and the intensity of the processes of their reworking, with the boundaries along the delta-front and the river fan of the Utulik and Pereemnaya. We reconstructed the formation process of the modern relief of this area of the underwater slope and determined a dominant role of the underwater-erosion processes in the formation of the modern relief, with the tectonic movements served as the “trigger” for them. The study revealed a direct correlation between the reworking of the ancient geomorphological surfaces and the occurrence of separate large underwater elevations or group ridges (remnants), canyons and linear depressions. It is determined that the pivotal role in the appearance of the modern relief of the underwater slope in the second area of extensive plano-convex (in section) and fan-shaped (in plan) delta-fronts of large rivers and debris fans enveloping the remnants. The existence of a steep underwater slope from the mouth of the Pereemnaya to the mouth of the Bol’shaya Tel’naya and of two large benches, and also the proximity of the maximum depths of the southern basin at the foot of this slope are explained by a more intense step-like lowering of this part of the lake when compared with the western part of the basin. This also accounts for the absence of large remnants in this part of the slope. The area of occurrence of lacustrine-fluvial and lacustrine-delta deposits of the Tankhoi paleobasin within the southern basin of Baikal is reconstructed. Four new hydrate-bearing structures associated with these deposits and morphologically pronounced in the vertex parts of the remnants were discovered. The morphological exploration indicators of the presence of new accumulations of gas hydrates on the underwater slopes of Baikal have been expanded.

America's Past-time and the Art of Diplomacy

As organizations and corporations construct an international reach, they become influential actors in foreign relations between sovereign countries. Particularly, while Major League Baseball continues to recruit players and build a large fan base across the globe, it increases its ability to facilitate civil relations between the United States and other nations. An exploration of how professional baseball provides a useful platform to improve diplomatic relations between the United States and Cuba best exemplifies how the League can promote change. Although the United States and Cuba have had a rather tumultuous relationship in recent history, a coordinated effort to improve the treatment of Cuban baseball players through changes in League rules and federal laws has the ability to spark a unified commitment to improved diplomacy. The proposed changes to improve relations with Cuba, can also be used by Major League Baseball and the United States to increase diplomatic success with other nations who have a vested interest in the success and fair treatment of their native baseball players.

Fan Similarity Model for the Fan–Intake Interaction Problem

Very high bypass ratio turbofans with large fan tip diameter are an effective way of improving the propulsive efficiency of civil aero-engines. Such engines, however, require larger and heavier nacelles, which partially offset any gains in specific fuel consumptions. This drawback can be mitigated by adopting thinner walls for the nacelle and by shortening the intake section. This binds the success of very high bypass ratio technologies to the problem of designing an intake with thin lips and short diffuser section, which is well matched to a low speed fan. Consequently, the prediction of the mutual influence between the fan and the intake flow represents a crucial step in the design process. Considerable effort has been devoted in recent years to the study of models for the effects of the fan on the lip stall characteristics and the operability of the whole installation. The study of such models is motivated by the wish to avoid the costs incurred by full, three-dimensional (3D) computational fluid dynamics (CFD) computations. The present contribution documents a fan model for fan–intake computations based on the solution of the double linearization problem for unsteady, transonic flow past a cascade of aerofoils with finite mean load. The computation of the flow in the intake is reduced to a steady problem, whereas the computation of the flow in the fan is reduced to one steady problem and a set of solutions of the linearized model in the frequency domain. The nature of the approximations introduced in the fan representation is such that numerical solutions can be computed inexpensively, while the main feature of the flow in the fan passage, namely the shock system and an approximation of the unsteady flow encountered by the fan are retained. The model is applied to a well-documented test case and compares favorably with much more expensive 3D, time-domain computations.