bluuebunny/crossref_metadata_2025 huggingface dataset:
Bone mineral density and composition in rat pregnancy: effects of streptozotocin‐induced diabetes mellitus and insulin replacement
Authors: Tein MS , Breen SA , Loveday BE , Devlin H , Balment RJ , Boyd RD , Sibley CP , Garland HO
Published: December 2014

A disturbed calcium homeostasis characterizes diabetic pregnancy. This study documents changes in bone mineral composition in diabetic pregnant rats and examines the effect of insulin replacement. Control pregnant (CP), diabetic pregnant (DP) and insulin‐treated DP (DPi) rats were assessed for femoral calcium and magnesium content, bone mineral density (BMD) and the ratio of hypertrophic to maturing and proliferative cells in the femoral growth plate. DP rats showed a significantly (P < 0.01) lower body weight, femoral weight and length than CP rats. Femoral calcium and magnesium content was also significantly (P < 0.05) lower in DP rats, as was ash weight. When calcium and magnesium were normalized for ash weight no significant differences were apparent. A significantly (P < 0.05) lower total BMD at the distal femur was seen in DP rats. This comprised a significantly (P < 0.01) lower trabecular BMD with no significant change in cortical BMD. A significantly (P < 0.05) higher ratio of hypertrophic to maturing and proliferative cells of the femoral growth plate was evident in DP animals. DPi rats showed normal blood glucose concentrations and femoral growth plate histology. DPi rats also showed normal femoral weight and length but only partially restored femoral ash weight and mineral content. Insulin failed to normalize total or trabecular BMD. Diabetes mellitus clearly has a marked effect on bone growth and mineral content in pregnancy which may be relevant to overall calcium homeostasis. The lower bone growth, bone calcium content and trabecular BMD may be unfortunate consequences of the marked hypercalciuria reported elsewhere in diabetes and may serve to maintain normocalcaemia in the disease.
A method for reversible permeabilization of isolated rat ventricular myocytes
Authors: Fawcett JM , Harrison SM , Orchard CH
Published: December 2014

A method is described that enables the cell membrane of isolated rat ventricular myocytes to be permeabilized and resealed while maintaining cell viability. Streptolysin O, a cholesterol‐binding cytolysin, was used to form pores in the surface membrane; subsequent incubation with 5% fetal bovine serum was used to reverse this permeabilization. The efficacy of membrane permeabilization and resealing was ascertained using a simultaneous double‐staining technique using propidium iodide, a marker for cells with permeabilized membranes, and fluorescein diacetate, a marker for viable cells. This procedure allowed a distinction to be made between dead cells, unpermeabilized cells and viable cells that had been successfully permeabilized and resealed. The accessibility of the cell interior during permeabilization was investigated by including fluorescein isothiocyanate (FITC)‐labelled dextrans (11, 38 and 148 kDa) and bovine serum albumin (67 kDa) in the permeabilization buffer, and localizing the FITC label using confocal microscopy following resealing. The confocal images showed that these molecules entered the cells and were retained after resealing. Following the permeabilization‐resealing protocol, cells appeared to have both normal morphology and response to electrical stimulation. Thus this appears to be a cheap, simple and effective method to introduce relatively large molecules into cardiac myocytes.
Cyclical passive stretch influences the mechanical properties of the inactive cat soleus
Authors: Roy RR , Pierotti DJ , Baldwin KM , Zhong H , Hodgson JA , Edgerton VR
Published: December 2014

The effects of cyclical, passive manipulation (PM, 30 min day(−1), 5 days week(−1) for 6 months) mimicking the length excursions observed during stepping on the mechanical and associated biochemical properties of the inactive cat soleus muscle were determined in five cats. Inactivity was produced via spinal cord isolation (SI), i.e. complete spinal cord transections at low thoracic and high sacral levels and bilateral dorsal rhizotomy between the transection sites. Passive manipulation was administered to one leg of each SI cat. Compared with normal controls, SI resulted in approximately 70% decrease in weight, an 80% decrease in maximum tetanic tension (Po) and an approximately 100% increase in maximum rate of shortening (Vmax) and myosin adenosine triphosphatase (mATPase) activity of the soleus. The passive manipulation regime partially ameliorated these effects. When compared with the control SI soleus, the SI‐PM soleus weight and maximum tetanic tension were 12 and 21% higher, respectively, and the Vmax and mATPase activity 21 and 12% (p > 0.05) lower, respectively. Thus, inactivity resulted in a smaller and faster muscle, whereas passive manipulation for only 30 min a day tended to maintain these properties closer to normal control values. The results suggest a potential therapeutic effect of short bouts of cyclical, passive manipulation on otherwise inactive skeletal muscles.
Gas handling in the caecum of the horse
Authors: Cottrell DF , Jones AF , Potter KE
Published: December 2014

Electromanometric recordings of caecal pressures were made in chronically cannulated ponies. Endoscopy allowed direct observation of the caecal base and cupola while recording intracaecal pressures and enabled a functional interpretation of caecal pressure profiles. Using gas‐tight seals, the caecal gas cap baseline pressure (tone) was usually below atmosphere, becoming less negative postprandially. Diurnal variations were observed in the amplitude and frequency of caecal pressure profiles and the direction of caecal movements, during which intra‐caecal gas cap pressures briefly became positive. A paraprandial (psychic) phase of enhanced caecal motility was observed. Manipulation of the caecal gas cap volume, by insufflation of nitrogen gas, demonstrated the capacity of the caecal base to regulate gas pressures and to eliminate fermenting gases.
The effects of substrate and fluid provision on thermoregulatory, cardiorespiratory and metabolic responses to prolonged exercise in a cold environment in man
Authors: Galloway SD , Maughan RJ
Published: December 2014

During prolonged exercise in a cold environment, fatigue is generally associated with a depletion of endogenous glycogen stores. This has lead many authors to hypothesize that the carbohydrate (CHO) content of fluids ingested in cool environments should be high, yet this hypothesis has not been specifically examined. In the present study, six healthy males cycled to exhaustion at approximately 80% of their maximum oxygen consumption (V2O,max) with either no drink (ND), a 15% CHO‐electrolyte drink (15% CHO) or a 2% CHO electrolyte drink (2% CHO). Dietary intake and exercise were replicated 2 days prior to each trial. Mean (S.D.) ambient temperature was 10.0 (0.3) degrees C with a relative humidity of 72 (2) % and an air velocity of approximately 0.7 m s(−1) on all trials. Weighted mean skin temperature was calculated, and rectal temperature and heart rate were recorded at rest, during exercise and at exhaustion. Venous samples were drawn before and during exercise and at exhaustion for determination of haemoglobin, haematocrit, blood metabolites and serum electrolytes and osmolality. Expired air was collected for calculation of VO2 and respiratory exchange ratio which were used to estimate rates of fuel oxidation. Ratings of perceived exertion (RPE) were also obtained. Exercise capacity was not different (P=0.49) between trials, with median (range) times to exhaustion of 90.6 (66.8−106.0), 97.7 (60.9−112.0) and 102.0 (77.1−170.7) min for the ND, 15% CHO and 2% CHO trials, respectively. The 15% CHO drink significantly (P < 0.05) elevated blood glucose concentration and total CHO oxidation compared with the ND trial. The 2% CHO drink significantly (P < 0.05) reduced the estimated change in plasma volume and resulted in a lower serum osmolality than the other two trials. No differences were observed in any thermoregulatory or cardiorespiratory responses between trials. These data suggest that maintenance of blood‐borne substrate and/or plasma volume does not influence exercise capacity in the cold, as is commonly reported during this type and intensity of exercise in warmer environments.
Autonomic control of submandibular protein secretion in the anaesthetized calf
Authors: Calvert PA , Heck PM , Edwards AV
Published: December 2014

The autonomic control of submandibular secretion has been investigated in fully weaned, anaesthetized calves 7 weeks after birth. Stimulation of the parasympathetic (chorda‐lingual) innervation invariably produced a flow of saliva, the rate of which was frequency dependent over the range 2‐8 Hz continuously. Neither the rate of flow nor the output of protein was enhanced by stimulating in bursts at relatively high frequencies. Stimulation of the sympathetic innervation (20 Hz for 1 s at 10 s intervals) alone produced a much slower flow of saliva but with a considerably higher protein content. Stimulation of both together produced no greater flow of saliva than occurred with either alone at the lower frequencies (2 and 4 Hz) but there was a pronounced synergy in respect of the secretion of protein. Following pre‐treatment with propranolol (1.0 mg kg‐1 i.v.), during on‐going chorda‐lingual stimulation at 4 Hz, intra‐arterial injections of 1 nmol of either vasoactive intestinal peptide (VIP) or pituitary adenylate cyclase activating peptide (PACAP) elicited an increase in the flow and protein output of about the same order of magnitude. Calcitonin gene‐related peptide (CGRP) also produced these same effects with roughly half the efficacy of VIP and PACAP but substance P had no detectable effect. It is concluded that VIP, PACAP and possibly CGRP are candidates for neurotransmitters with a role in the control of secretion in this gland.
Effects of variations in dietary calcium and phosphorus supply on plasma and bone osteocalcin concentrations and bone mineralization in growing pigs
Authors: Nicodemo ML , Scott D , Buchan W , Duncan A , Robins SP
Published: December 2014

Growing pigs were fed diets supplying 45% (low), 70% (intermediate) and 100% (high) recommended dietary allowances of calcium (the Ca:P ratio was kept constant), but otherwise adequate in nutrients. The effects of varying calcium and phosphorus intakes on bone and plasma osteocalcin were monitored. Mineral content of the diet did not affect feed conversion and live weight gain. Plasma phosphorus concentrations decreased significantly in pigs fed a low mineral diet compared with those fed the high mineral diet, but there were no changes in plasma calcium and osteocalcin concentrations. Bones from the low mineral group had marked reductions in dry matter, calcium and phosphorus contents, as well as increased collagen, pyridinoline and deoxypyridinoline concentrations: osteocalcin concentrations in bone were unaffected by treatment. The results showed no direct link between osteocalcin and the degree of bone mineralization.
Chronic intermittent immobilization of male rats throughout sexual development: a stress protocol
Authors: Almeida SA , Anselmo-Franci JA , Rosa Silva e AA , Carvalho TL
Published: December 2014

A stress protocol‐‐6 h of daily immobilization‐‐was applied throughout male rat sexual development. Immobilization caused a small reduction in food intake and body weight gain whereas pair‐fed animals had a marginal decrease only in body weight gain. Stress, confirmed by increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone, caused a decrease in plasma luteinizing hormone (LH) after 15 and 60 days of immobilization and in plasma testosterone after 60 days, but produced an opposite androgenic response in pubertal animals (15 days of immobilization). A persumed sympathetic over‐stimulation is suggested to account for increased testosterone levels in pubertal stressed rats.
Interactions among iron, calcium, phosphorus and magnesium in the nutritionally iron‐deficient rat
Authors: Campos MS , Barrionuevo M , Alferez MJ , Gomez-Ayala AE , Rodriguez-Matas MC , Lopez Aliaga I , Lisbona F
Published: December 2014

We studied the development of nutritional iron deficiency 0, 10, 20, 30 and 40 days after the intake of a semisynthetic diet lacking iron (diet 0) and the possible interactions with calcium, phosphorus and magnesium in both control rats and rats after 40 days of iron deficiency. During this period, iron deficiency was found to produce stress in the rats, as evidenced by high levels of cortisol in the serum. High levels of parathyroid hormone (PTH) were also found. There was a considerable increase in the absorption of calcium, phosphorus and magnesium, but the phosphorus and magnesium balance decreased and that of calcium remained practically unchanged, although there was an increase in calcium urinary elimination. Despite the noticeable degree of bone demineralization, which was evident in the femur, serum levels of calcium, phosphorus and magnesium remained constant. The present study shows that severe nutritional ferropenic anaemia provokes significant alterations in the metabolism of calcium, phosphorus and magnesium. We conclude that these alterations should be taken into account in the treatment of this pathology, given its prevalence and the fact that it may exacerbate other pathologies, particularly those related to the metabolism of calcium and phosphorus.
Age‐related changes in oxygen and nutrient uptake by hindquarters in newborn pigs during cold‐induced shivering
Authors: Lossec G , Lebreton Y , Hulin JC , Fillaut M , Herpin P
Published: December 2014

Newborn pigs rely essentially on shivering thermogenesis in the cold. In order to understand the rapid postnatal enhancement of thermogenic capacities in piglets, the oxygen and nutrient uptake of hindquarters was measured in vivo in 1‐ (n = 6) and 5‐day‐old (n = 6) animals at thermal neutrality and during cold exposure. The hindquarters were considered to represent a skeletal muscle compartment. Indirect calorimetry and arterio‐venous techniques were used. The cold challenge (23 C at 1 day old and 15 C at 5 days old for 90 min) induced a similar increase (+90 %) in regulatory heat production at both ages. Hindquarters blood flow was higher at 5 days than 1 day old at thermal neutrality (26 +/− 3 vs. 17 +/− 1 ml min‐1 (100 g hindquarters)‐1) and its increase in the cold was much more marked (+65 % at 5 days old vs. +25 % at 1 day old). Oxygen extraction by the hindquarters rose from 30–35 % at thermal neutrality to 65–70 % in the cold at both ages. The calculated contribution of skeletal muscle to total oxygen consumption averaged 34–40 % at thermal neutrality and 50–64 % in the cold and skeletal muscle was the major contributor to regulatory thermogenesis. Based on hindquarters glucose uptake and lactate release, carbohydrate appeared to be an important fuel for shivering. However, net uptake of fatty acids increased progressively during cold exposure at 5 days old. The enhancement in muscular blood supply and fatty acid utilization during shivering is probably related to the postnatal improvement in the thermoregulatory response of the piglet.
Role of luminal volume changes in the increase in pulmonary blood flow at birth in sheep
Authors: Hooper SB
Published: December 2014

The mechanism by which pulmonary blood flow increases and pulmonary vascular resistance decreases after birth is not fully understood. The aim of this study was to simulate the decrease in lung volume caused by the onset of air‐breathing at birth and determine whether it can duplicate the changes in pulmonary blood flow and vascular resistance that occur at this time. In chronically catheterized fetal sheep near term (145 days of gestation), fetal pulmonary arterial blood flow was measured, using coloured microspheres, before and after fetal lung liquid volumes were reduced from 52.2 +/− 2.7 to 21.2 +/− 1.6 ml kg‐1. During the 30 min period following the reduction in lung liquid volume, the pulmonary‐to‐systemic arterial pressure difference decreased from 6.8 +/− 1.2 mmHg (pulmonary > systemic) to 1.6 +/− 0.5 mmHg. Reducing the volume of fetal lung liquid increased pulmonary blood flow from 59.1 +/− 10.5 to 204.2 +/− 40.4 ml min‐1 (100 g tissue)‐1 and reduced pulmonary vascular resistance from 0.53 +/− 0.20 to 0.14 +/− 0.04 mmHg min ml‐1 (100 g tissue)‐1. We conclude that a reduction in fetal lung liquid volume, which simulates the reduction in lung volume that occurs at birth, causes a 3‐ to 4‐fold increase in pulmonary blood flow and a reduction in pulmonary vascular resistance of a similar magnitude. Thus, the reduction in lung volume associated with the lung changing from a liquid‐ to an air‐filled organ, may partly account for the increase in pulmonary blood flow and decrease in pulmonary vascular resistance at birth.
Differences in human antagonistic ankle dorsiflexor coactivation between legs; can they explain the moment deficit in the weaker plantarflexor leg?
Authors: Maganaris CN , Baltzopoulos V , Sargeant AJ
Published: December 2014

The present study examined the hypothesis that the antagonistic ankle dorsiflexor coactivation level during maximum isometric voluntary plantarflexion (MVC) is a function of ankle angle. Six male subjects generated plantarflexion and dorsiflexion MVC trials at ankle angles of −15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg having the knee flexed at an angle of 90 deg. In all contractions surface EMG measurements were taken from tibialis anterior and soleus which were considered representative muscles of all dorsiflexors and plantarflexors, respectively. Antagonistic dorsiflexor coactivation was expressed as normalized EMG and moment. Calculations of the antagonistic dorsiflexor moment were based on the tibialis anterior EMG‐dorsiflexor moment relationship from contractions at 50, 40, 30, 20 and 10 % of the dorsiflexion MVC moment. In both legs dorsiflexor coactivation level followed an open U‐shaped pattern as a function of ankle angle. Differences of 9 and 14 % (P < 0.05) were found in the measured net plantarflexion MVC moment between legs at ankle angles of −15 and +30 deg, respectively. No difference (P > 0.05) was found in the calf circumference between legs. Differences were found in the antagonistic dorsiflexor coactivation between legs at ankle angles of −15 and +30 deg. In the weaker leg the antagonistic EMG measurements were higher by 100 and 45 % (P < 0.01) and the estimated antagonistic moments were higher by 70 and 43 % (P < 0.01) compared with the weaker leg at −15 and +30 deg, respectively. This finding was associated with a decreased range of motion (ROM) in the weaker leg (14 %, P < 0.01), such that no difference (P > 0.05) was found in dorsiflexor antagonistic coactivation between legs at end‐range ankle angles. The findings of the study (i) have to be taken into consideration when estimating musculoskeletal loads in the lower extremity, (ii) imply that stretching training can result in a stronger plantarflexion at end‐range ankle angles through inhibition of the dorsiflexors, and (iii) imply a neural drive inadequacy during a plantarflexion MVC at end‐range angles.
Inflammation and oxidative stress during intermittent hypoxia: the impact on chemoreception
Authors: Iturriaga Rodrigo , Moya Esteban A. , Del Rio Rodrigo
Published: December 2014

New Findings

What is the topic of this review?

This article describes the contribution of oxidative stress and pro‐inflammatory cytokines to the enhanced carotid body chemosensory responsiveness to the hypoxia and systemic hypertension induced by chronic intermittent hypoxia.

What advances does it highlight?

Chronic intermittent hypoxia enhances the carotid body chemosensory discharge during normoxia and hypoxia, leading to sympathetic overactivity and hypertension. New evidence suggests that chronic intermittent hypoxia increases pro‐inflammatory cytokines. Here, we discuss the role of inflammation in the alterations of the carotid chemoreceptor function as well as the cardiorespiratory alterations following chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH), the main characteristic of obstructive sleep apnoea, enhances carotid body (CB) chemosensory discharges during normoxia and hypoxia and elicits hypertension. These alterations are attributed to oxidative stress, because antioxidants prevent the enhanced CB chemosensory discharges and the hypertension. In this report, we discuss new evidence supporting the suggestion that oxidative stress‐induced upregulation of pro‐inflammatory cytokines (i.e. tumour necrosis factor‐α and interleukin‐1β) in the CB is involved in the chemosensory potentiation and the hypertension following CIH. Anti‐inflammatory treatment with ibuprofen prevents the increased tumour necrosis factor‐α and interleukin‐1β levels in the CB and the hypertension, but does not reduce the enhanced chemosensory hypoxic response and the local oxidative stress in the CB. In contrast, antioxidant treatment with ascorbic acid prevents the increase in cytokine concentrations and CB oxidative stress, the chemosensory potentiation and the hypertension. Thus, the enhanced CB chemosensory responses to hypoxia depend critically on the oxidative stress, but not on the increased tumour necrosis factor‐α and interleukin‐1β in the CB. We discuss a possible role for pro‐inflammatory cytokines in development of the hypertension produced by CIH, acting on cardiorespiratory centres located in the CNS.
Dynamic Experimental Investigations of a Bypass Dual Throat Nozzle
Authors: Gu Rui , Xu Jinglei
Published: December 2014

The bypass dual throat nozzle (BDTN) does not consume any secondary injection from the other part of the engine, while it can produce steady and efficient vectoring deflection similar to the conventional dual throat nozzle (DTN). A BDTN model has been designed and subjected to dynamic experimental study. The main results show that: (1) The frequency spectrums of the dynamic pressures are different between each thrust vector state. (2) The variation rates of dynamic vector of the new BDTN can reach as high as 50 deg/s, 40 deg/s, and 34 deg/s under nozzle pressure ratio NPR = 3, 5, and 10, separately. (3)The dynamic hysteresis time is less than 1 ms.
Fuzzy Control of Supercapacitor Current in Hybrid Diesel Generator/Fuel Cell Marine Power System
Authors: Hajizadeh Amin , Hossein Shahirinia Amir , Yu David C.
Published: December 2014

This paper presents a power control strategy for a marine power system made up of a hybrid diesel generator, a fuel cell, and an energy storage unit. For this purpose, a self-tuning fuzzy control is designed to manage the power generation between power sources during different maneuverings and voltage disturbances (both balanced and unbalanced) in an AC system. As a solution, a current control strategy using a voltage source converter is presented. Simulation results show the response of the whole system under a test driving cycle and this variety of voltage disturbance conditions. They illustrate the performance, including power flow control and voltage disturbance ride-through capability, of the proposed control strategy.
Numerical Simulation of Stirling Engines Using an Unsteady Quasi-One-Dimensional Approach
Authors: Andersson Niklas , Eriksson Lars-Erik , Nilsson Martin
Published: December 2014

An existing computer code for solving the quasi-one-dimensional (Q1D) flow equations governing unsteady compressible flow in tubes with smoothly varying cross section areas has been adapted to the simulation of the oscillatory flow in Stirling engines for engine design purposes. By utilizing an efficient smoothing algorithm for the area function that preserves the total volume of the tube, it has been possible to achieve a highly accurate and fully conservative numerical scheme. Submodels for wall friction and heat transfer have been added, enabling the simulation of gas heaters, gas coolers, and regenerators. The code has been used for the modeling of an α-type Stirling engine and validated for a range of operating conditions with good results.
Electric Field-Assisted Additive Manufacturing Polyaniline Based Composites for Thermoelectric Energy Conversion
Authors: Decker Bruce Y. , Gan Yong X.
Published: December 2014

Polyaniline (PANi) based composites were made by electric force assisted nanocasting. The PANi matrix was mixed with thermoelectric Bi–Te alloy nanoparticles. The uniform dispersion of the nanoparticles in the polymer was achieved via electric field assisted casting. The nanoparticles can enhance the thermoelectricity, specifically increase the Seebeck coefficient. Structure analysis and Seebeck effect experiments were performed. The microstructure of the composite materials was studied by the use of electron microscopy. The preliminary results show that the nanocomposites are n-type with an average Seebeck value of 30 μV/K. The electrical resistance of the composites is about 35 MΩ.
Design for Control of Wheeled Inverted Pendulum Platforms
Authors: Vasudevan Hari , Dollar Aaron M. , Morrell John B.
Published: December 2014

In this paper, we study five aspects of design for wheeled inverted pendulum (WIP) platforms with the aim of understanding the effect of design choices on the balancing performance. First, we demonstrate analytically and experimentally the effect of soft visco-elastic tires on a WIP showing that the use of soft tires enhances balancing performance. Next, we study the effect of pitch rate and wheel velocity filters on WIP performance and make suggestions for design of filters. We then describe a self-tuning limit cycle compensation algorithm and experimentally verify its operation. Subsequently, we present an analytical simulation to study the effects of torque and velocity control of WIP motors and describe the tradeoffs between the control methodologies in various application scenarios. Finally, to understand if motor gearing can be an efficient alternative to bigger and more expensive direct drive motors, we analyze the effect of motor gearing on WIP dynamics. Our aim is to describe electromechanical design tradeoffs appropriately, so a WIP can be designed and constructed with minimal iterative experimentation.
On the Stability of Rigid Multibody Systems With Applications to Robotic Grasping and Locomotion
Authors: Várkonyi Péter L.
Published: December 2014

This paper shows that the equilibria of a wide class of multibody systems with quasi-rigid, frictional, or frictionless supports correspond to local minima of their potential energy; hence they are stable against small perturbations of external forces. This is a generalization of a theorem by Howard and Kumar on the stability of a single rigid body held by a gripper. It is also demonstrated that ambiguous equilibria (those, which coexist with the possibility of accelerating motion) may be stable. These results help finding safe grasps on nonrigid objects and assessing the stability of quasi-static robots moving over complex terrains.
Dynamic Modeling of a Closed Cycle Gas Turbine CHP Plant With a Nuclear Heat Source
Authors: Kikstra Jan Foeke , Verkooijen Adrian H. M.
Published: December 2014

The High Temperature Gas-cooled Reactor is a promising concept for inherently safe nuclear power generation. This paper deals with dynamic modeling of the energy conversion system of a combined heat and power plant, based on a helium cooled reactor in combination with a closed cycle gas turbine system. The model will be used to design and test a control system and to analyze transients following incidents. A one-dimensional flow model describing the helium flow and the two-phase water flow is used through the whole plant, with different source terms in different pieces of equipment. A stage-by-stage model is produced for the radial compressor and axial turbine. Other models include the recuperator, water/helium heat exchangers a natural convection evaporator, valves, etc. With this model, open-loop responses from controlled parameters (shaft speed, temperatures and pressures) on changes of reactor power, valve-positions etc. have been established.
Cooled Cooling Air Systems for Turbine Thermal Management
Authors: Bruening Greg B. , Chang Won S.
Published: December 2014

This paper evaluates the feasibility and potential impact on overall engine performance when utilizing the heat sink sources available in a gas turbine engine for improved turbine thermal management. A study was conducted to assess the application of a heat exchanger to cool the compressor bleed air normally used air for cooling turbine machinery. The design tradeoffs of this cooled cooling air approach as we’ll as the methodology used to make the performance assessment will be addressed.

The results of this study show that the use of a cooled cooling air (CCA) system can make a positive impact on overall engine performance. Minimizing the complexity and weight of the CCA system, while utilizing advanced, high temperature materials currently under development provide the best overall solution in terms of design risk and engine performance.
Phase-Lagged Boundary Condition Methods for Aeroelastic Analysis of Turbomachines: A Comparative Study
Authors: Srivastava R. , Bakhle Milind A. , Keith Theo G. , Stefko G. L.
Published: December 2014

In the present work a comparative study of phase-lagged boundary condition methods is carried out. The relative merits and advantages of time-shifted and the Fourier decomposition methods are compared. Both methods are implemented in a time marching Euler/Navier-Stokes solver and are applied to a flat plate helical fan with harmonically oscillating blades to perform the study. Results were obtained for subsonic as well as supersonic inflows. Results for subsonic inflow showed good comparisons with published results and between the two methods along with comparable computational costs. For the supersonic inflow, despite the presence of shocks at the periodic boundary results from both the methods compared well, however, Fourier decomposition method was computationally more expensive. For linear flowfield Fourier decomposition method is best suited, especially for work-station environment. The time-shifted method is better suited for CRAY category of computers where fast input-output devices are available.
Numerical and Experimental Investigations on the Flow in a 4-Stage Turbine With Special Focus on the Development of a Radial Temperature Streak
Authors: Bonn Dieter , Funke Harald , Gier Jochen
Published: December 2014

In the development of modern gas turbines the increase of the turbine inlet temperature is restricted by the need to cool the first stages of the turbine. In addition the flow leaving the combustor is thermally inhomogeneous. Since the blade cooling has to be designed for the actual local hot gas temperatures, it is important to know how these temperature inhomogeneities develop and attenuate inside the multistage flow passage.

In this investigation the flow inside a 4-stage turbine, which is set up in a test rig at the Institute of Steam and Gas Turbines, Aachen University of Technology, is calculated with a state-of-the-art fully three-dimensional Navier-Stokes solver based on an accurate finite volume scheme. The stator and rotor rows are coupled via mixing planes. The turbine is a scaled down original turbine with realistic axial gaps.

The homogeneous reference case is qualified by comparison to recent experimental data gathered at the test rig. Therefore, the flow is extensively measured at several locations. In a second step a radial temperature streak is set at the inlet for the same point of operation. The results show the development of the temperature streak through the four stages. With this information the underlying mixing processes are described and analysed. It is found that the hot streak segregation effect is present in all four stages.
The Origin of Turbulent Spots
Authors: Johnson Mark W. , Dris Antonis
Published: December 2014

It has been suggested that a turbulent spot is formed when a transient separation occurs in the laminar boundary layer and this criterion has been successfully used by Johnson and Ercan [1996,1997] to predict bypass transition for boundary layers subjected to a wide range of freestream turbulence levels and streamwise pressure gradients. In the current paper experimental results are presented which support the premise that the formation of turbulent spots is associated with transient separation. Near wall hot wire signals in laminar and transitional boundary layers are analysed statistically to produce probability distributions for signal level and trough frequency. In the laminar period the signal level is normally distributed, but during the inter-turbulent periods in the transitional boundary layer the distribution is truncated at the tower end, i.e. the lowest velocity periods in the signal disappear, suggesting that these are replaced during transition by the turbulent periods. The number of these events (troughs) also correlates with the number of turbulent spots during early transition.

A linear perturbation theory is also used in the paper to compute the streamlines through a turbulent spot and its associated calmed region. The results indicate that a hairpin vortex dominates the flow and entrains a low momentum fluid stream from upstream with a high momentum stream from downstream and then ejects the combined stream into the turbulent spot. The hairpin can only exist if a local separation occurs beneath its nose and the current results suggest that this separation is induced when the instantaneous velocity in the near wall signal drops below 50% of the mean.
Effect of Internal Coolant Crossflow Orientation on the Discharge Coefficient of Shaped Film Cooling Holes
Authors: Gritsch Michael , Saumweber Christian , Schulz Achmed , Wittig Sigmar , Sharp Edwin
Published: December 2014

Discharge coefficients of three film-cooling hole geometries are presented over a wide range of engine like conditions. The hole geometries comprise a cylindrical hole and two holes with a diffuser shaped exit portion (a fanshaped and a laidback fanshaped hole). For all three hole geometries the hole axis was inclined 30° with respect to the direction of the external (hot gas) flow. The flow conditions considered were the hot gas crossflow Mach number (up to 0.6), the coolant crossflow Mach number (up to 0.6) and the pressure ratio across the hole (up to 2).

The effect of internal crossflow approach direction, perpendicular or parallel to the main flow direction, is particularly addressed in the present study. Comparison is made of the results for a parallel and perpendicular orientation, showing that the coolant crossflow orientation has a strong impact on the discharge behavior of the different hole geometries. The discharge coefficients were found to strongly depend on both hole geometry and crossflow conditions.

Furthermore, the effects of internal and external crossflow on the discharge coefficients were described by means of correlations used to derive a predicting scheme for discharge coefficients. A comparison between predictions and measurements reveals the capability of the method proposed.
An Experimental Investigation of the Flow in a 1½ Stage Axial Turbine With Regard to a High Level of Cooling-Air Injection
Authors: Reinmöller U. , Gallus H. E.
Published: December 2014

Experimental investigations of flow mixing due to film cooling of turbine blades have been performed. In a 1½-stage axial air turbine cooling gas (cool nitrogen down to −130 °C) was blown directly onto the leading edge of the first stator by special gas injector devices. In order to provide a database for the verification of numerical codes and to give an impression of the mixing process the gas has been injected at different radial positions. Furthermore the cooling massflow and cooling temperature were varied. The measuring data were obtained using pneumatic 5-hole probes with temperature sensors.

The presented experimental data were simultaneous acquired in the planes behind both stators and the rotor. The results are compared and, discussed with reference measurements without cooling gas injection. It is shown that the effect of cooling gas injection is apparent in the wake of the first stator where it causes a small decrease in the pressure distribution as a result of increased flow mixing. Behind the first stator differences in the circumferentially averaged pitchwise flow angle due to the injected gas were not measured. Furthermore, temperature measurements clearly show the effect of the cooling gas injection in all planes. Even behind the second stator the different magnitudes of the temperature distribution are caused by the various injection of cooling gas.
Performance of a Turbine Airfoil With Multiple Film Cooling Stations: Part II — Aerodynamic Losses
Authors: Drost U. , Bölcs A.
Published: December 2014

In the present study the aerodynamic performance of a turbine NGV airfoil was investigated, cooled from several showerhead, pressure and suction side stations. Film cooling heat transfer and effectiveness on this airfoil was examined in part I of this paper. Tests were conducted in a linear cascade at an exit Reynolds number of 1.45e6 and an exit Mach number 0.8. Density ratio effects were studied with air and CO2 injection, matching the densities by correctly adjusting the coolant temperature.

In terms of a primary loss coefficient, neglecting the coolant kinetic energy, coolant injection increased the losses by 20–30% compared to solid blade losses, but depended only weakly on the coolant mass flow rate. A slight loss increase for increasing injection up to 2% coolant mass flow was noted, followed by a weak decrease for further augmented coolant mass flow rates. The primary losses appeared to be independent of the coolant medium and temperature.

Thermodynamic loss coefficients including the loss of coolant kinetic energy, monotonically increased with coolant mass flow rates. To check the validity of CO2 injection for the simulation of high density ratios, the latter has been matched using strongly cooled air and heated CO2. The thermodynamic losses did not match at constant density ratio, but at constant coolant Mach number, when compared at constant coolant mass flow rates. Reporting the losses to the total pressure ratio (momentum flux ratio) yielded excellent scaling emphasizing the usefulness of the momentum flux ratio for film cooling loss scaling.
High Resolution Measurements of Local Effectiveness by Discrete Hole Film Cooling
Authors: Baldauf S. , Schulz A. , Wittig S.
Published: December 2014

Local adiabatic film cooling effectiveness on a flat plate surface downstream a row of cylindrical holes was investigated. Geometrical parameters like blowing angle and hole pitch as well as the flow parameters blowing rate and density ratio were varied in a wide range emphasizing on engine relevant conditions. An IR-thermography technique was used to perform local measurements of the surface temperature field. A spatial resolution of up to 7 data points per hole diameter extending up to 80 hole diameters downstream of the ejection location was achieved. Since all technical surface materials have a finite thermoconductivity, no ideal adiabatic conditions could be established. Therefore, a procedure for correcting the measured surface temperature data based on a Finite Element analysis was developed. Heat loss over the backside of the testplate and remnant heat flux within the testplate in lateral and streamwise direction were taken into account. The local effectiveness patterns obtained are systematically analyzed to quantify the influence of the various parameters. As a result, a detailed description of the characteristics of local adiabatic film cooling effectiveness is given. Furthermore, the locally resolved experimental results can serve as a data base for the validation of CFD-codes predicting discrete hole film cooling.
Evaluation and Application of Data Sources for Assessing Operating Costs for Mechanical Drive Gas Turbines in Pipeline Service
Authors: Smalley Anthony J. , Mauney David A. , Ash Daniel I. , Clowney Sam L. , Pappas George P.
Published: December 2014

This paper evaluates and demonstrates how the public domain data provided by individual interstate pipeline companies to FERC, when combined with individual company equipment lists, can be used to regress industry information on cost of operations and maintenance, fuel gas used, and cost of fuel and power. The paper describes the methods of analysts and identifies their limitations. The paper presents results of such regression analysis as average and variance of cost and fuel usage for industrial gas turbines and aeroderivative gas turbines. It provides further comparisons between gas turbine prime movers, reciprocating engine prime movers, and electric motor drives, and presents annual costs per installed horsepower as a function of turbine size. The paper is based on work performed for PRC International and the Gas Research Institute.
The Role of Carbon Monoxide in NO2 Plume Formation
Authors: Feitelberg Alan S. , Correa Sanjay M.
Published: December 2014

Through a series of computational studies, carbon monoxide has been identified as an important promoter of NO oxidation to NO2 in combustion turbine exhaust gas at intermediate temperatures (450 to 750°C). NO2 formation is accompanied by enhanced CO burnout at these temperatures. Perfectly stirred reactor and plug flow reactor calculations indicate that concentrations of CO as low as 50 ppmv in exhaust gas containing 25 ppmv NO can result in the conversion of 50% of the NO to NO2 in less than 1 second. NO2 concentrations as low as 15 ppmv can result in visible, yellow-brown plumes from large diameter exhaust stacks. If NO2 plumes are to be prevented, then designers of gas turbines and heat recovery steam generators need to be aware of the relationships between time, temperature, and composition which cause NO2 to form in exhaust gas.

Reaction path analysis indicates that the mutually promoted oxidation of CO and NO occurs through a self-propagating, three-step chain reaction mechanism. CO is oxidized by OH, (R2)CO+OH→CO2+Hwhile NO is oxidized by HO2:(R23)NO+HO2→NO2+OHIn a narrow temperature range, the H-atom produced by R2 can react with O2 in a three body reaction to yield the hydroperoxy radical needed in R23:(R9)H+O2+M→HO2+Mwhere M is any third body. The observed net reaction isCO+O2+NO→CO2+NO2which occurs stoichiometrically at temperatures below about 550°C. As the temperature increases, additional reaction pathways become available for H, HO2, and OH which remove these radicals from the chain and eventually completely decouple the oxidation of CO from NO.

An abbreviated set of elementary chemical reactions, including 15 species and 33 reactions, has been developed to model CO-enhanced oxidation of NO to NO2. This reaction set was derived from a larger reaction set with more than 50 species and 230 elementary chemical reactions, and was validated by comparison of PSR and PFR calculations using the two sets.
Comparison Between Measured and Predicted Wall Temperatures in a Gas Turbine Combustor
Authors: Hicks R. A. , Wilson C. W.
Published: December 2014

On of the major considerations in the development of advanced gas turbine engines are increased thrust to weight ratio and reduced development and operating costs. Improvements in engine thrust require an increase in combustion chamber heat release and inlet pressures. However, increasing the amount of heat release will also result in an increase in the radiative heat flux to the combustion chamber walls, proving detrimental to the operational life time of the combustor. To maximise combustor life, different cooling devices can be incorporated into the combustion chamber design. The effectiveness with which these devices are implemented is important and in the absence of a reliable predictive numerical tools, is difficult to quantify without undertaking expensive and timely testing. A computer analysis tool, based on a network model approach, has previously been developed to analyse airflow distributions in complex combustor geometries. A recent variant of this model has incorporated the Discrete Transfer radiation model, along with other convective and conductive sub-models, to account for heat transfer. These models have been validated against thermocouple measurements of wall temperature obtained in a sectored research combustor. The results of this comparison indicate that, whilst the model is capable of predicting the trends in wall temperature, it is currently unable to reproduce the magnitude of wall temperature with a greater accuracy than 80 K. However, the versatility of the discrete transfer model suggests that further improvements in accuracy are possible.
Flow Instability Within a Diffusing, Annular S-Shaped Duct
Authors: Norris G. , Dominy R. G. , Smith A. D.
Published: December 2014

Experimental measurements have been made on a representative, high radius ratio, inter-turbine diffuser with and without internal load-bearing struts. It is shown that without the struts fitted the severe, local diffusion experienced within the test duct results in a casing surface flow separation. The addition of a representative row of load bearing struts which intrude into the separation zone is shown to exacerbate the flow separation by increasing the local diffusion rate. The casing surface flow separation, for the non-swirling case presented here, clearly demonstrates a low frequency instability. It has been shown previously that the propagation of wakes through a diffusing duct provides a mechanism for the creation of pressure driven secondary flows. For this duct configuration it is shown that these secondary flows act to suppress the unsteady flow separation. Direct comparisons between CFD and experimental results show good agreement especially for the case with the struts in place.
Deterministic Stress Modeling of Hot Gas Segregation in a Turbine
Authors: Busby Judy , Sondak Doug , Staubach Brent , Davis Roger
Published: December 2014

Simulation of unsteady viscous turbomachinery flowfields is presently impractical as a design tool due to the long run times required. Designers rely predominantly on steady-state simulations, but these simulations do not account for some of the important unsteady flow physics. Unsteady flow effects can be modeled as source terms in the steady flow equations. These source terms, referred to as Lumped Deterministic Stresses (LDS), can be used to drive steady flow solution procedures to reproduce the time-average of an unsteady flow solution. The goal of this work is to investigate the feasibility of using inviscid lumped deterministic stresses to model unsteady combustion hot streak migretion effects on the turbine blade tip and outer air seal heat loads. The LDS model is obtained from an unsteady inviscid calculation. The inviscid LDS model is then used with a steady viscous computation to simulate the time-averaged viscous solution.

The feasibility of the inviscid LDS model is demonstrated on a single stage, three-dimensional, vane-blade turbine with a hot streak entering the vane passage at mid-pitch and mid-span. The steady viscous solution with the LDS model is compared to the time-averaged viscous, steady viscous and time-averaged inviscid computations. The LDS model reproduces the time-averaged viscous temperature distribution on the outer air seal to within 2.3%, while the steady viscous has an error of 8.4%, and the time-averaged inviscid calculation has an error of 17.2%. The solution using the LDS model is obtained at a cost in CPU time that is 26% of that required for a time-averaged viscous computation.