Experimental Investigation of the Transient Flow in Roots Blower

Rotary positive displacement machines are common method to pump flow in various process industries. Their performance highly depends on the operational clearances. It is widely believed that computational fluid dynamics (CFD) can help understanding and reducing internal leakage flows. However, Developments of grid generating tools for use of CFD in rotary positive displacement machines have not yet been fully validated. Thereby arising a need to validate these models that help in better understanding of the leakage flows. Roots blower is a good representative of positive displacement machines and as such is convenient for optical access to analyse flows in in such machines. This paper describes the setup of the experimental test rig with the optical Roots blower in the Centre for Compressor Technology at City, University of London and the first results obtained using three different flow visualization methods. These are namely i) the high-speed camera (HC), ii) the continuous time resolved PIV (CPIV) and iii) the instantaneous PIV obtained with double pulse PIV laser and double shutter camera (IPIV). Test results from these three tests are compared and discussed in the paper. The CPIV test shows the movement of the vortex and the general shape of the flow field clearly but is not sufficient to calculate velocity vectors of high-velocity particles due to the limitation of the laser and camera. The IPIV test can produce quantitative velocity vector images of the internal flow but needs improvement to look into the leakage flow. The work described in this paper is a part of the large project set to evaluate characteristics of the internal flow in rotary positive displacement machines and to characterize leakage flows. The objective is to enable further improvements in 3D CFD analysis of leakage flows in rotary positive displacement machines and ultimately lead to the improvement in the performance of rotary positive displacement machines

Path instabilities of light particles rising in a liquid with background rotation

The present paper reports on experimental observations performed on 2–6 mm low-density polystyrene particles rising freely in a water-glycerol mixture for the liquid at rest as well as with slow background rotation (axisymmetric solid body rotation around the vertical axis). Particle trajectories were studied in the Reynolds-numbers range of 200<Re<800 at a fixed rotation rate of Ω=0.81/s. Both the trajectory measurements and the wake visualization indicate that there are differences in the wake structure of the particles as well as in the path instabilities compared to those in quiescent fluid. In the swirling flow, the two-threaded wake mode is dominant up to Reynolds numbers of about 500 with typical spiral-type trajectories until vortex shedding commences. In contrast, under quiescent flow conditions vortex shedding already occurs above Re=230, and the particles predominantly move in zig-zagging paths. Thus, the presence of background rotation is able to suppress vortex shedding and to delay the transition. For the co-rotating observer, the radius of the spiral-type path is comparable to that of the transversal motion under quiescent flow conditions. Therefore, the magnitude of lateral lift-forces is not greatly affected by the presence of the swirl

Numerical and Experimental Analysis of Transient Flow in Roots Blower

The performance of rotary positive displacement machines highly depends on the operational clearances. It is widely believed that computational fluid dynamics (CFD) can help understanding internal leakage flows. Developments of grid generating tools for analysis of leakage flows by CFD in rotary positive displacement machines have not yet been fully validated. Roots blower is a good representative of positive displacement machines and as such is convenient for optical access in order to analyse internal flows. The experimental investigation of flow in optical roots blower by phase-locked PIV (Particle Image Velocimetry) performed in the Centre for Compressor Technology at City, University of London provided the velocity field suitable for validation of the simulation model. This paper shows the results of the three-dimensional CFD transient simulation model of a Roots blower with the dynamic numerical grids generated by SCORG and flow solution solved in ANSYS CFX flow solver to obtain internal flow patterns. The velocity fields obtained by simulation agree qualitatively with the experimental results and show the correct main flow features in the working chamber. There are some differences in the velocity magnitude and vortex distribution. The flow field in roots blower is highly turbulent and three-dimensional. The axial clearances should be included, and the axial grids should be refined in the simulation method. The paper outlines some directions for future simulation and experimental work. The work described in this paper is a part of the large project set to evaluate characteristics of the internal flow in rotary positive displacement machines and to characterize leakage flow

Experimental and numerical investigation of tip leakage flows in a roots blower

Computational fluid dynamics (CFD) can help in understanding the nature of leakage flow phenomena inside the rotary positive displacement machines (PDMs). However, due to the lack of experimental results, the analysis of leakage flows in rotary PDMs by CFD has not yet been fully validated. Particle image velocimetry (PIV) tests with a microscopic lens and phase-lock were conducted to obtain the velocity field around the tip gap in an optical Roots blower. The three-dimensional unsteady CFD model of the Roots blower with the dynamic grids generated by Screw Compressor Rotor Grid Generation (SCORG) was established to predict the gap flow under the same operating conditions. The images obtained by the PIV tests were analyzed and some factors which compromise the quality of test results in the gap flow were identified, such as reflections and transparency of the window. The flow fields obtained by CFD have the same flow pattern and velocity magnitude as the experimental results in the majority of observed regions but overestimate the leakage flow velocity. The CFD results show a vortex induced by the leakage flow in the downstream region of the gap. The flow losses in the tip gap mainly happen at the entrance upstream of the gap. Finally, some suggestions for future work are discussed

Eagle syndrome

A thirty-eight-year-old male patient was referred by the general practitioner to our department for recurrent throat pain radiating to head and neck for a few months. The pain was more prominent on the left side, especially during swallowing, and sometimes accompanied by a creaking noise and sensation of a ‘click’. Physical examination showed a slightly hard bulge on the left upper neck. Previous medical history was not helpful and laboratory findings were normal. Ultrasound of the neck, as a first investigation, showed no abnormalities. In addition, enhanced computed tomo - graphy of the neck was performed. Coronal reconstruction, as shown in Fig. A, revealed total ossification of the stylohyoid ligaments, from the origin on the styloid process to the insertion on the lesser horn of the hyoid bone, as well as enlargement of both styloid processes, more pronounced on the left. Pseudo-articulation between the left stylohyoid ligament and styloid process, also shown in Fig. A and more in detail on the three-dimensional reconstruction in Fig. B, caused the local swelling in the left upper neck. These radiographic findings accompanied by the patient’s complaints, is known as “Eagle Syndrome”. Because of the minor clinical repercussions, conservative treatment was optioned

Numerical investigation of the bending of slenderwall-mounted cylinders in low reynolds number flow

The aim of the present studies is construction of reference data for the prediction of the bending of sensor hairs close to the wall in a boundary-layer flow. Three-dimensional direct numerical simulations (DNS) of finite cylinders in single and tandem configuration are carried out. The numerical setup is guided by a towingtank experiment performed at the Technical University of Freiberg. All numerical configurations are chosen to complement and extend the experimental work. The bending curve of the cylinders is estimated by a static approach according to 1st -order Euler-Bernoulli beam theory. Based on the forces, extrapolated from the DNS of the flow field, the influence of wall- and top-end effects and Reynolds numbers between 5 and 40 is examined more deeply. Also, varying positions of cylindrical tandem configurations in stream- and spanwise directions are investigated. The present work shows good agreement between simulation and experiment

Rationale, design and methods of the HEALTHY study physical education intervention component

The HEALTHY primary prevention trial was designed to reduce risk factors for type 2 diabetes in middle school students. Middle schools at seven centers across the United States participated in the 3-year study. Half of them were randomized to receive a multi-component intervention. The intervention integrated nutrition, physical education (PE) and behavior changes with a communications strategy of promotional and educational materials and activities. The PE intervention component was developed over a series of pilot studies to maximize student participation and the time (in minutes) spent in moderate-to-vigorous physical activity (MVPA), while meeting state-mandated PE guidelines. The goal of the PE intervention component was to achieve ≥150 min of MVPA in PE classes every 10 school days with the expectation that it would provide a direct effect on adiposity and insulin resistance, subsequently reducing the risk of type 2 diabetes in youth. The PE intervention component curriculum used standard lesson plans to provide a comprehensive approach to middle school PE. Equipment and PE teacher assistants were provided for each school. An expert in PE at each center trained the PE teachers and assistants, monitored delivery of the intervention and provided ongoing feedback and guidance

Sensing of minute airflow motions near walls using pappus-type nature-inspired sensors

This work describes the development and use of pappus-like structures as sensitive sensors to detect minute air-flow motions. We made such sensors from pappi taken from nature-grown seed, whose filiform hairs' length-scale is suitable for the study of large-scale turbulent convection flows. The stem with the pappus on top is fixated on an elastic membrane on the wall and tilts under wind-load proportional to the velocity magnitude in direction of the wind, similar as the biological sensory hairs found in spiders, however herein the sensory hair has multiple filiform protrusions at the tip. As the sensor response is proportional to the drag on the tip and a low mass ensures a larger bandwidth, lightweight pappus structures similar as those found in nature with documented large drag are useful to improve the response of artificial sensors. The pappus of a Dandelion represents such a structure which has evolved to maximize wind-driven dispersion, therefore it is used herein as the head of our sensor. Because of its multiple hairs arranged radially around the stem it generates uniform drag for all wind directions. While still being permeable to the flow, the hundreds of individual hairs on the tip of the sensor head maximize the drag and minimize influence of pressure gradients or shear-induced lift forces on the sensor response as they occur in non-permeable protrusions. In addition, the flow disturbance by the sensor itself is limited. The optical recording of the head-motion allows continuously remote-distance monitoring of the flow fluctuations in direction and magnitude. Application is shown for the measurement of a reference flow under isothermal conditions to detect the early occurrence of instabilities

Measuring the value of air quality: application of the spatial hedonic model

This study applies a hedonic model to assess the economic benefits of air quality improvement following the 1990 Clean Air Act Amendment at the county level in the lower 48 United States. An instrumental variable approach that combines geographically weighted regression and spatial autoregression methods (GWR-SEM) is adopted to simultaneously account for spatial heterogeneity and spatial autocorrelation. SEM mitigates spatial dependency while GWR addresses spatial heterogeneity by allowing response coefficients to vary across observations. Positive amenity values of improved air quality are found in four major clusters: (1) in East Kentucky and most of Georgia around the Southern Appalachian area; (2) in a few counties in Illinois; (3) on the border of Oklahoma and Kansas, on the border of Kansas and Nebraska, and in east Texas; and (4) in a few counties in Montana. Clusters of significant positive amenity values may exist because of a combination of intense air pollution and consumer awareness of diminishing air quality

Consensus Paper: Radiological Biomarkers of Cerebellar Diseases

Hereditary and sporadic cerebellar ataxias represent a vast and still growing group of diseases whose diagnosis and differentiation cannot only rely on clinical evaluation. Brain imaging including magnetic resonance (MR) and nuclear medicine techniques allows for characterization of structural and functional abnormalities underlying symptomatic ataxias. These methods thus constitute a potential source of radiological biomarkers, which could be used to identify these diseases and differentiate subgroups of them, and to assess their severity and their evolution. Such biomarkers mainly comprise qualitative and quantitative data obtained from MR including proton spectroscopy, diffusion imaging, tractography, voxel-based morphometry, functional imaging during task execution or in a resting state, and from SPETC and PET with several radiotracers. In the current article, we aim to illustrate briefly some applications of these neuroimaging tools to evaluation of cerebellar disorders such as inherited cerebellar ataxia, fetal developmental malformations, and immune-mediated cerebellar diseases and of neurodegenerative or early-developing diseases, such as dementia and autism in which cerebellar involvement is an emerging feature. Although these radiological biomarkers appear promising and helpful to better understand ataxia-related anatomical and physiological impairments, to date, very few of them have turned out to be specific for a given ataxia with atrophy of the cerebellar system being the main and the most usual alteration being observed. Consequently, much remains to be done to establish sensitivity, specificity, and reproducibility of available MR and nuclear medicine features as diagnostic, progression and surrogate biomarkers in clinical routine