Search results

AXIAL flow fans were originally developed from aircraft airscrews and therefore can be claimed as children of aeronautical science. Their use has been confined in aeronautics to wind tunnels and radial engine cooling until the advent of ‘pressurized’ cabins. In this case ventilation requirements have caused an axial flow fan to be used. These fans have been gradually developed in the ventilation industry and they are replacing centrifugal fans where these would have been used previously. Price and noise level have not been in the axial flow fans' favour in this fight but they have advantages of higher efficiency, ease of installation and non‐overloading power characteristic. Latest developments in aerodynamic design and production technique suggest that the disadvantages are being overcome. This note is intended to furnish a general introduction to the design features of axial flow fans for aircraft ventilation.

A method for optimizing net positive suction head required of axial‐flow pumps has been proposed by the present author, which is based on the two‐dimensional potential flow model and without considering the tip gap effect. The objective of the paper is to confirm if the method is just and feasible for the case of viscous fluid flow in impellers with tip gap.

A series of steady, three‐dimensional, noncavitating and cavitating, turbulent, incompressible flows of water through two axial‐flow pump impellers were calculated by using CFD code Fluent. The two impellers included a reference one with constant circulation at outlet and an optimized one with variable circulation designed with the author's method and code. In computations, the throttling and unthrottling approaches were used, respectively. Comparison of hydraulic performance, averaged flow variables at the impeller inlet and exit, flow in the tip gap, flow variables on blade surfaces and suction performance between the optimized and reference impellers was made.

It was confirmed that the optimized impeller has better hydraulic and suction performances. The method for optimizing with variable flow circulation profile along blade span at the outlet to impeller is proper and practical. Additionally, an unstable regime in the head curves of two impellers is presented. In the regime, a stall occurs on the pressure side of the blade and a hysteresis exists, which causes a hysteresis‐loop.

The effect of suction entry on flow is represented approximately by using a free‐vortex and uniform axial velocity. The diffusing component behind the impellers is not taken into account. The unsteadiness of flow is not considered, which would have a connection with stall pattern in an axial‐flow impeller.

The hydraulic and suction performances and flow variables of two axial‐flow pump impellers with tip clearance are obtained successfully with CFD. Stall and hysteresis as well as hysteresis‐loop in head curve are observed by using throttling and unthrottling approaches.

The control of an inventory where spare parts demand is infrequent has always been difficult to manage because of the randomness of the demand, as well as the existence of a large proportion of zero values in the demand pattern. The purpose of this paper is to propose a just-in-time (JIT) spare parts availability approach by integrating condition monitoring (CM) with spare parts management by means of proportional hazards models (PHM) to eliminate some of the shortcomings of the spare parts demand forecasting methods.

In order to obtain the event data (lifetime) and CM data (first natural frequency) required to build the PHM for the spares demand forecasting, a series of fatigue tests were conducted on a group of turbomachinery blades that were systematically fatigued on an electrodynamic shaker in the laboratory, through base excitation. The process of data generation in the numerical as well as experimental approaches comprised introducing an initial crack in each of the blades and subjecting the blades to base excitation on the shaker and then propagating the crack. The blade fatigue life was estimated from monitoring the first natural frequency of each blade while the crack was propagating. The numerical investigation was performed using the MSC.MARC/2016 software package.

After building the PHM using the data obtained during the fatigue tests, a blending of the PHM with economic considerations allowed determining the optimal risk level, which minimizes the cost. The optimal risk point was then used to estimate the JIT spare parts demand and define a component replacement policy. The outcome from the PHM and economical approach allowed proposing development of an integrated forecasting methodology based not only on failure information, but also on condition information.

The research is simplified by not considering all the elements usually forming part of the spare parts management study, such as lead time, stock holding, etc. This is done to focus the attention on component replacement, so that a just-in-time spare parts availability approach can be implemented. Another feature of the work relates to the decision making using PHM. The approach adopted here does not consider the use of the transition probability matrix as addressed by Jardine and Makis (2013). Instead, a simulation method is used to determine the optimal risk point which minimizes the cost.

This paper presents a way to address some existing shortcomings of traditional spare parts demand forecasting methods, by introducing the PHM as a tool to forecast spare parts demand, not considering the previous demand as is the case for most of the traditional spare parts forecasting methods, but the condition of the parts in operation. In this paper, the blade bending first mode natural frequency is used as the covariate in the PHM in a laboratory experiment. The choice of natural frequency as covariate is justified by its relationship with structural stiffness (and hence damage), as well as being a global parameter that could be measured anywhere on the blade without affecting the results.

The Paris/Le Bourget International Air and Space Show is the world's oldest international show and is of considerable importance. It will have 548 exhibitors from 23 countries and there will be 165,000 square metres of display area — with 10,000 square metres for the out‐door static exhibits. The numbers of chalets is to be increased by 55.

The purpose of this study is to design and develop an environmentally controlled enclosure for commercial three-dimensional (3D) printers.

Computational fluid dynamics (CFD) simulations and experimental testing investigated various designs for environmentally controlled enclosures. CFD simulations provided the necessary information to select the optimal and feasible design, whereas experimental testing validated the CFD simulation results. An environmentally controlled environment allowed test samples to be printed at several relative humidity (RH) settings (20% RH, 50% RH and 80% RH). The test samples were characterized at both the macro and micro scales. The macroscale characterization was conducted using the static tensile testing procedure, while the microscale polymer material properties were determined using atomic force microscopy.

An environmentally controlled enclosure was designed and built to produce airflow in the print region with an average RH uniformity of over 0.70. Three batches of ASTM D638 standard test samples were printed at 20% RH (low RH), 50% RH (mid RH) and 80% RH (high RH). Macroscale characterization showed that the samples printed at lower humidity had statistically significantly higher tangent modulus, ultimate tensile strength and rupture strength. atomic force microscopy studies have also verified these results at the microscale and nanoscale. These studies also showed that a high humidity environment interacts with melted polylactic acid, causing additional surface roughness that reduces the strength of 3D-printed parts.

There is a need for stronger and higher-quality 3D-printed parts in the additive manufacturing (AM) market. This study fulfills that need by designing and developing an environmentally controlled add-on enclosure for the AM market.

The purpose of this paper is to determine the validity and inter-/intra-laboratory repeatability of the first part of a novel, three-phase experimental procedure using a sweating Torso device.

Results from a method comparison study (comparison with the industry-standard sweating guarded hotplate method) and an inter-laboratory comparison study are presented.

A high correlation was observed for thermal resistance in the method comparison study (r=0.97, p<0.01) as well as in the inter-laboratory comparison study (r=0.99, p<0.01).

The authors conclude that the first phase of the standardised procedure for the sweating Torso provides reliable data for the determination of the dry thermal resistance of single and multi-layer textiles, and is therefore suitable as standard method to be used by different laboratories with this type of device. Further work is required to validate the applicability of the method for textiles with high thermal resistance.

This study provides the first “round-robin” data for measuring thermal resistance using a Torso device. In future publications the authors will provide similar data examining the repeatability of measurements that quantify combined heat and mass transfer.

Chester Street, Aston, Birmingham, 6. The ‘Donald’ Patent Barrel Lifter Truck and Stand, the three‐in‐one appliance. Barrels up to 7 cwts. lifted and transported by one man. ‘Donald’ Patent Barrel Lifter Stands for Oil Stores.

The Quick‐Click system self retaining pin automatically locks in place when it is installed and cannot be removed without a special tool. Designed as replacements for clevis pins with cotter pins or clip rings, a circular C shaped spring is located in a tapered neck at the point end. A finger pressure of 4 or 5 pounds is all that is needed to install the pin and as it enters the hole, the pressure pushes the spring back to the smallest diameter of the tapered‐neck portion of the pin, where it easily compresses to allow the pin to be pushed completely through the hole. As the end of the pin exits from the far end of the hole, the spring expands to larger than hole size. Attempts to push out the pin without the removal tool cause the spring to ride up on the larger end of the tapered neck, where it cannot be compressed. Since it won't compress, it holds the pin firmly in place. Removal force without the special tool is more than 8200lb for the 9/16in. pin and 220lb for the small #10 pin, and is thus virtually tamper‐proof.

The purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.

A wall-modeled large eddy simulation (WMLES) has been performed for a spanwise 3D extrusion of the central section of the fan stage. Computations were performed for three different operating conditions, from nominal (Q_N) to off-design (85 per cent Q_N and 70 per cent Q_N) working points. Circumferential periodic conditions were introduced to reduce the extent of the computational domain. The post-processing procedure enabled the segregation of unsteady deterministic features and turbulent scales. The simulations were experimentally validated using wake profiles and turbulent scales obtained from hot-wire measurements.

The transport of rotor wakes and both wake–vane and wake–wake interactions in the stator flow field have been analyzed. The description of flow separation, particularly at off-design conditions, is fully benefited from the LES performance. Rotor wakes impinging on the stator vanes generate a coherent large-scale vortex shedding at reduced frequencies. Large pressure fluctuations in the stagnation region on the leading edge of the vanes have been found.

LES simulations have shown to be appropriate for the assessment of the design of an axial fan, especially for specific operating conditions for which a URANS model presents a lower performance for turbulence description.

This paper describes the development of an LES-based simulation to understand the flow mechanisms related to the rotor–stator interaction in axial fan stages.

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan.

A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region.

It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes.

Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy.

The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.