Circumferential Profiles Research Articles

Investigation of Pressure Pulsation and Vibration of the Internally Geared Screw Compressor

Abstract The Internally Geared Screw Machine (IGSM) is a relatively novel and promising type of positive displacement compressor concept that takes inspiration from classic gerotor pumps. The IGSM uses two rotors rotating in the same direction about parallel axes while maintaining continuous contact between both rotors which isolates several working chambers. By using ported end plate, the IGSM can determine the timing of the fluid entering and exiting the working chamber. There are several key advantages to the IGSM over traditional twin-screw compressors including reduction of the rotor to casting leakage, elimination of the blow hole area, reduction in sliding velocity at the point of contact, and a uniform circumferential rotor temperature profile. Although there is some research regarding the geometric profiling and chamber modeling of this type of machine, there is no research currently available on the pressure pulsation and vibration characteristics of the IGSM. The purpose of this paper is to provide an initial look into the pressure pulsation and vibration characteristics of the IGSM and how they differ from that of a traditional twin-screw machine. By explicating the key differences between the IGSM and the industry standard twin-screw compressor, this paper aims to better understand an important yet underdeveloped area of IGSM design.

A Novel Design Method for Chip Flute of Indexable Insert Drill Used at Large Drilling Depth

The design of the chip flute in indexable insert drills significantly influences chip removal efficiency, drill diameter deflection, and drill deformation in the metal drilling process, which are crucial for maintaining drill stability and minimizing deviations in the diameter of the drilled hole. However, traditional chip flute designs fail to meet production standards when drilling deep holes in 42CrMo, particularly at depths reaching up to seven times the hole diameter. This study introduces an innovative optimization method for the chip flute design of indexable insert drills specifically intended for metal deep-cutting applications, which involves refining both the cross-sectional and circumferential profiles of the chip flute. A novel combined cross-section for the chip flute was developed and tested against the conventional double U-profile in drilling experiments on 42CrMo. Based on the chip shape of the inner and outer inserts, the inner insert flute section is designed into a U-shaped section and the outer insert flute section is designed into trapezoidal section, respectively, so as to increase the proportion of the effective chip removal area in the chip flute, which reduces the chip flute section area and increases the core thickness of the tool holder. Additionally, the circumferential profile was enhanced through orthogonal simulation experiments. The findings revealed that the drill diameter deflection using the newly designed combined cross-section was reduced by 21.76% compared to the traditional double U-profile in the metal drilling process. The indexable insert drill featuring this optimized chip flute configuration exhibited significant improvements in the drill diameter deflection, drill deformation, and drilled hole diameter accuracy, outperforming the standard drill design.

The influence of the free runners on the decelerated swirling flow from the draft tube cone of hydraulic turbines.

Abstract Nowadays the renewable energy plays an key role in the development of safe and clean energy. Worldwide and especially in Europe the development of renewable energy is focused on development of new wind and solar power plants. Accordingly, these energy technologies introduce high power fluctuations in the electrical system, which are necessary to compensate by other energy sources. To compensate these power fluctuations, the electrical systems use new technologies as high-capacity electric batteries or classical technologies as hydropower. The new technologies as the batteries are used rarely, while the hydropower remain the only technology to response quickly at the electrical systems requirements. The hydropower with the hydraulic turbines has the capability to adapt faster at the electrical system requirements, but for hydraulic turbines this requirement comes with hydrodynamic consequences. Accordingly, at the outlet of the hydraulic turbines (in the conical diffuser), the hydraulic instabilities are developed (vortex rope occurs) accompanied by high pressure fluctuations. The present paper proposes adding free runner at the inlet of the conical diffuser, which rotates on an axle, with null momentum. For this purpose, have been designed and manufactured a series of four free (additional) runners (with different numbers of blades) to assess the performances of this method. Experimental investigations of unsteady pressure and velocity profiles using LDV system were performed downstream of the free runner. The velocity measurements have been performed on three survey axes, by measuring the meridian and circumferential velocity profiles. The unsteady pressure measurements were achieved at the conical diffuser wall on two levels. To better analyse the relevance of the free runners, the Fourier transform is applied on pressure signals. The results will clarify the functionality and limitations of this method for swirling flow control.

Experimental study of erosion in heat exchangers immersed in fluidized beds

Fluidized beds can be used as solar energy receivers in beam-down concentrated solar power plants. The fact that solid particles can withstand temperatures over 1,000°C is promising because it would mean higher thermal efficiencies than conventional concentrated solar power plants (CSP, that use molten salts, whose maximum operating temperature is limited to about 560°C). Nonetheless, immersed heat exchangers are exposed to erosion because fluidized particles impinge on their surfaces. The multiple variables of a multiphase flow and the uncertainties of the material detachment process make erosion a complex problem that stills not fully solved.The aim of this study is to conceive an experimental procedure to measure erosion on cylindrical probes immersed in a lab-scale high temperature fluidized bed (able to operate up to 1,000°C and atmospheric pressure), simulating a tube of a heat exchanger in a fluidized bed working at expected temperatures in CSP applications.Preliminary results at ambient temperature are presented in this study. Silica sand particles were fluidized with air and erosion was measured on cylindrical probes made of aluminium 5027. Silica sand was characterized with a microscope before and after each test to determine its size distribution and shape. Several parameters (diameter, mass, and circumferential profile) of each probe were also studied before and after each test. Different fluidization velocities were implemented to assess the influence of the flow rate on erosion.

Quantitative Performance Evaluation of Commonly Used Colormaps for Image Display in Myocardial Perfusion Imaging: Analysis based on Perceptual Metrics.

To quantitatively evaluate the performance of the most used colormaps in image display using perceptual metrics and to what extent these measures are congruent with the true intensity or uptake of pixels at different levels of defect severity in simulated cardiac images. Six colormaps, labeled "Gray", "Thermal", "Cool", "CEqual", "Siemens" and "S Pet" extracted from FIJI ImageJ software are included. Colormap data are converted from the red, green, blue color space to CIELAB. Perceptual metrics for measuring "color difference" were calculated, including difference (ΔE76) and "speed". The pairwise color difference in every two levels or entries is visualized in a 2-dimensional "heatmap distance matrix" for each colormap. Curves are plotted for each colormap and compared. In addition, to apply this technique to clinical images, simulated short-axis cardiac slices with incremental defect severity (10% grading) were employed. The circumferential profile curves of true pixel intensity, lightness or luminance, and color difference are plotted simultaneously for each defect severity to visualize the concordance of the three curves in various colormaps. In 0% defect, all the curves are at the highest level, except for "s pet", in that the lightness is not at its maximum value. In the phantom with 10% defect (or 90% of maximum value), discrepancies among curves appear. In "Siemens", the ΔE76 drops sharply. In "Siemens" colormap, the ΔE76 drops sharply. In 80% defect, ΔE76 curve, in "gray" colormap drops more slowly than other curves of other colormaps. In "s pet", lightness curve rises paradoxically, although the count intensity and ΔE76 curve match. In 70% defect, again, the curves are in good agreement in "thermal", "Siemens" and "cequal". However, a consistent lag exists in "gray". Up to 50% defect, curves maintain their expected pattern, but in defects more severe than 40%, lightness and ΔE76 curves in "cool" and "cequal" rise paradoxically, and in "thermal", they start to slow down in descent. In "Siemens", falling pattern of the three curves continues. For "s pet" colormap, an erratic pattern of lightness and ΔE76 curves exists. Of 6 colormaps investigated for estimating defect severity, "grayscale" is less favorable than others and "thermal" performs slightly better. "S pet" or rainbow, which is used traditionally by many practitioners, is strongly discouraged. The "Siemens" colormap suffers from decreased discriminating power in the range of mild to moderate/severe. In contrast, the "cool" and "cequal" colormaps outperform the other colormaps employed in this study to some extent, although they have some shortcomings.

Effect of pulsation parameters on the spatial and temporal variation of flow and heat transfer characteristics in liquid metal cross flow the in-line tube bundle

Liquid metal has a broad application prospect in tube bundle heat exchangers because of its excellent thermal conductivity. However, conventional in-line tube bundle arrangements often exhibit limited secondary flow, so new methods are urgently needed to improve heat transfer. The topic of this paper is to combine two methods, liquid metal cross flow tube bundle and pulsating flow, to improve the heat transfer performance in-line tube bundles. Firstly, the applicability of the model was validated through experimental data from existing literature, encompassing overall flow dynamics, heat transfer performance, and circumferential pressure distribution around the tubes. Subsequently, numerical simulations are conducted involving liquid metal cross flow in-line tube bundles at varying pulsating frequencies, amplitudes, and Reynolds numbers. Circumferential pressure distributions and temperature profiles for individual tubes were analyzed and compared. The amplitude of reduction in thermal resistance compared to the no-oscillation condition increases gradually from a minimum of 8 % in the first row to a maximum of 40 % in the third row, while the reduction in the rear row of tubes is similar to that of the third row. Remarkably, a reversal in the trend of thermal resistance for the first three rows of tubes under pulsating flow were observed, contrasting conventional flow except for the case with an amplitude of 0.1. By analyzing the local transient flow field distribution near single tube and the corresponding circumferential heat transfer performance, the influence of the vortex evolution characteristics on the heat transfer performance at different phases of the pulsating velocity is revealed, which transient Nu is up to three times that of flow with no pulsating. Finally, a series of coherence analyses reveal that as frequency rises, turbulence exhibits a richer spectrum of small-scale vortex structures, intricately linked to enhanced energy cascade efficiency. Amplitude augmentation intensifies velocity fluctuations, particularly at high amplitudes, resulting in substantial energy peak amplification. The integrated heat transfer performance PEC factor varies in the range of 1.25 to 1.51 for all the conditions simulated in this paper, which indicates that the liquid metal coupled pulsating flow approach can significantly increase the comprehensive performance of the tube bundle heat exchangers. These findings hold significant promise for advancing heat exchanger design and enhancing thermal efficiency, with implications for various engineering applications.

Form Shear Stress Correction in Bulk Flow Analysis of Grooved Seals Based on Effective Film Thickness

Abstract Bulk flow models for grooved annular seals provide computationally efficient static and dynamic response predictions, though heavy reliance on empirical relationships often leads to undesirable levels of uncertainty. The flow complexity caused by the grooves adds difficulty to shear stress modeling for these seals. This study seeks to improve shear stress modeling for grooved seals through the identification and quantification of the additional bulk flow shear stress contributions within the groove region. Through single groove computational fluid dynamics (CFD) simulations and an effective film thickness analysis framework, the additional groove shear stress component is identified as a form shear stress (FSS) due to its clear relationship to the effective film thickness behavior. The FSS is quantified as a correction to traditional shear stress definitions. Predictive models for the FSS are developed as functions of the ratio of circumferential to axial Reynolds number and the total resultant Reynolds number. Implementation of the FSS models into a simplified bulk flow method delivers leakage predictions for three seal cases within 10% of the experimental results and qualitative agreement in predicted circumferential velocity profiles while eliminating the need for an assumed groove loss coefficient. This is the first paper to utilize an effective film thickness-based procedure to quantify and model the FSS component in grooved seal bulk flow analysis. The demonstrated predictive capability and widespread applicability of the models and approach presented in this paper provide an avenue for significant improvements in grooved seal bulk flow prediction accuracy through improved shear stress modeling.

Investigation of pipelines defect localization for fusion reactor by using T(0,1) mode ultrasonic guided waves

The stable operation of a fusion reactor depends on the reliable functioning of various accessory systems, many of which comprise extensive pipelines with different diameters and diverse cladding. Defects in pipelines can occur due to manufacture, thermal stress, and fatigue, threatening the systems’ safety and reliability. Ultrasonic guided waves (UGWs) testing offers a promising approach for remotely locating these minute defects. The study explores non-dispersive fundamental torsional guided (T(0,1)) waves, particularly their influence on minor defect detection in stainless steel pipes. Both finite element simulations and experimental trials reveal that reflection coefficients, indicative of defect presence, rapidly escalate from 64 to 128 kHz. The optimal frequency for minor defect detection lies between 128 and 180 kHz. A significant finding from the circumferential distribution spectrum and angle profile reveals pipe diameter's dominant influence on the reflection energy distribution concentration. Furthermore, this highlights the unique ability of T(0,1) guided waves to precisely locate defects in the circumferential direction within large-diameter pipes over long distances. The results underscore the promising potential of UGWs testing in complex pipelines of fusion reactors.

Numerical Investigation into the Temperature Profile of a PHWR Channel Containing a Disassembled Fuel Bundle During a Postulated Accident Condition

A reactor core overheats due to decay heat generated in the fuel when an effective cooling medium is unavailable, such as in a loss-of-coolant accident combined with a loss of emergency core coolant. If the heat generated is not effectively dissipated, then at extreme temperatures, the structural strength of the bundle assembly may deteriorate, leading to slumping of fuel elements onto the inner wall of the pressure tube. It is essential to examine the temperature behavior of the channel containing fuel pins in a disassembled state in order to comprehend the impact of further thermally induced deformations in the channel during postulated accident conditions. Capturing the temperature of channel components at each circumferential position from experiments is extremely difficult; thus, a modeling tool is necessary to obtain a thorough circumferential temperature profile. This paper presents a numerical study that aims to study the temperature distributions in a 1-m-long pressurized heavy water reactor (PHWR) channel containing a disassembled fuel bundle. The channel geometry and the boundary conditions implemented were obtained from the experiment. A temperature profile for each channel element at every circumferential and axial location was obtained. A thorough comparison of the predicted and the reported experimental values was performed, and it was found that the predicted temperature behavior of the channel was consistent with the experimental data. Further simulations with different fuel element configurations and decay powers may be carried out; in addition, the results obtained may be used for coupled thermal-mechanical and thermal-mechanical-chemical simulations.

Improving air-water two-phase flow pumping in centrifugal pumps using novel grooved front shrouds

The present investigations aim to improve the gas-liquid two-phase transport in centrifugal pumps using a novel front shroud design with macroscopic grooves. This increases the secondary flow strength and the two-phase mixing, boosting the performance. A total of 23 different circumferential and radial groove profiles were numerically investigated to identify the best configuration leading to the highest mixing efficiency. Three different loads were considered, i.e., part load, optimal point, and overload. Additionally, the performance of the novel designs was compared with that of the established alternatives, involving two different clearance gaps and/or an inducer. While circumferential grooves already lead to a slightly improved specific delivery work, radial grooves improve noticeably the pump efficiency and deliver a very high two-phase mixing compared to other traditional pump configurations. Under conditions of optimal loading, the utilization of circumferential grooves led to a phase mixing enhancement of approximately 19.5%, whereas the implementation of radial grooves exhibited a notable improvement in mixing efficiency by 64.8% compared to the standard gap. The radial design R14 is superior to all other designs regarding efficiency and phase mixing. It is therefore recommended for transporting gas-liquid two-phase flows.

Application of 4-D ultrasound-derived regional strain and proteomics analysis in Nkx2-5-deficient male mice.

The comprehensive characterization of cardiac structure and function is critical to better understanding various murine models of cardiac disease. We demonstrate here a multimodal analysis approach using high-frequency four-dimensional ultrasound (4DUS) imaging and proteomics to explore the relationship between regional function and tissue composition in a murine model of metabolic cardiomyopathy (Nkx2-5183P/+). The presented 4DUS analysis outlines a novel approach to mapping both circumferential and longitudinal strain profiles through a standardized framework. We then demonstrate how this approach allows for spatiotemporal comparisons of cardiac function and improved localization of regional left ventricular dysfunction. Guided by observed trends in regional dysfunction, our targeted Ingenuity Pathway Analysis (IPA) results highlight metabolic dysregulation in the Nkx2-5183P/+ model, including altered mitochondrial function and energy metabolism (i.e., oxidative phosphorylation and fatty acid/lipid handling). Finally, we present a combined 4DUS-proteomics z-score-based analysis that highlights IPA canonical pathways showing strong linear relationships with 4DUS biomarkers of regional cardiac dysfunction. The presented multimodal analysis methods aim to help future studies more comprehensively assess regional structure-function relationships in other preclinical models of cardiomyopathy.NEW & NOTEWORTHY A multimodal approach using both four-dimensional ultrasound (4DUS) and regional proteomics can help enhance our investigations of murine cardiomyopathy models. We present unique 4DUS-derived strain maps that provide a framework for both cross-sectional and longitudinal analysis of spatiotemporal cardiac function. We further detail and demonstrate an innovative 4DUS-proteomics z-score-based linear regression method, aimed at characterizing relationships between regional cardiac dysfunction and underlying mechanisms of disease.

Surface morphology of blended molding pellets made of desert caragana and maize stover

The surface morphology of biomass pellets can provide data for the contact mechanics fractal model between the molding pellet and hole in biomass molding machines and for predicting wear of the molding hole. In this study, desert caragana (Caragana korshinskii) was mixed with residue from maize production, crushed, and compressed into pellets, which were used to collect data on their circumferential surface roughness profile, density, diameter, and hardness. The results showed that frictional wear occurs during contact between the forming hole and the molding particles, increasing the diameter d0 of the forming hole and the diameter d of the molding particles. The density ρ and hardness HD of the molded pellets decreased as their diameter d increased, and the ρ and HD of caragana were higher in autumn than in summer. The values of the roughness parameters Ra, Rc and Rz of the molded particles increased with their diameter d. The maximum material rate Mr2 value of the roughness’s central profile remained at 86% with the increase of diameter d. Molded particles had surface roughness kurtosis Rku>3 and roughness skew Rsk<0 with the increase of diameter d. The surface of molded particles was spiky and negatively skewed, and with a low number of spikes.

The Effect of the Rotating Disk Geometry on the Flow and Flux Enhancement in a Dynamic Filtration System

A numerical study was conducted to investigate the effect of rotating patterned disks on the flow and permeate flux in a dynamic filtration (DF) system. The DF system consists of a rotating patterned disk and a stationary housing with a circular flat membrane. The feed flow is driven by the rotating disk with the angular velocity ranging from 200 to 1000 rpm and the applied pressure difference between inlet and outlet ports. Wheel-shaped patterns are engraved on the disk surfaces to add perturbation to the flow field and improve the permeate flux in the filtration system. Five disks with varying numbers of patterns were used in numerical simulations to examine the effects of the number of patterns and the angular velocity of the disk on the flow and permeate flux in the DF system. The flow characteristics are studied using the velocity profiles, the cross-sectional velocity vectors, the vortex structures, and the shear stress distribution. The wheel-shaped patterns shift the central core layer in the circumferential velocity profile towards the membrane, leading to higher shear stresses at the membrane and higher flux compared to a plain disk. When the number of patterns on the disk exceeded eight at a fixed Reynolds number, there were significant increases in wall shear stress and permeate flux compared to a plain disk filtration system with no pattern.

Circumferential spatial tooth profile modification of flexspline for strain wave gear (A novel method and a case study)

Circumferential spatial tooth profile modification of flexspline for strain wave gear (A novel method and a case study)

Development of Translucent Design Philosophy for the Cyclic Pattern Design of Fan Outlet Guide Vanes

Abstract The fan systems of typical high bypass civil engines encounter strong flow distortions originating in the intake and the bypass duct. These flow distortions cause the fan stage operation point to vary from its design intent, thus reducing the fan stage performance and increasing low engine-order fan blade forcing. A cyclic pattern design for the fan Outlet Guide Vanes (OGV) can be effectively used to recover the fan stage performance and to control its system-level aeromechanical behavior. This paper presents the development of an OGV pattern design philosophy using the numerical experimentation technique. Multiple fan-intake unsteady computational fluid dynamic computations are conducted by clocking the circumferential pressure profile at the fan exit. The study revealed that a mild, low-harmonic fan back pressure profile with a suitable clocking position is able to improve the fan rotor efficiency and reduce the first engine order (1EO) fan forcing simultaneously. Such a profile can be generated by designing a cyclic OGV pattern that allows the bifurcation potential fields of controlled intensity and phase to pass through the OGV blade row, thus termed the translucent design philosophy. Further, a sensitivity study is performed to assess the effects of simultaneous distortions upstream and downstream of the fan. The study showed that a correctly clocked intra-stage static pressure profile can consistently improve both the performance and aeromechanical behavior of fan systems having different intake lengths and at different flight conditions. The implementation of the proposed translucent design philosophy in a new OGV pattern design tool is discussed.

Application Of LDV Profile Sensor Technology For Velocity Determination In Small Axial Gaps

In development of Ventricular Assist Devices (VADs), Computational Fluid Dynamics (CFD) have arise as a powerful tool to gain insights on flow topologies within rotary blood pumps. Information regarding flow patterns and shear-stress distributions is of enormous importance, since flow induced blood damage as well as platelet activation is at-tributed to shear rates. Although methods for verification of numerical results are available, a lack of experimental validation is recognizable. To enable an experimental validation (i) hydraulic properties as well as flow patterns need to be preserved and (ii) a non-intrusive optical measurement technique needs to be capable of resolving flow topolo-gies appearing in rotary blood pumps. In this paper references to address (i) are provided and the focus is placed on (ii) by presenting a methodology to resolve flow topologies by usage of LDV Profile Sensor technology. This paper serves as a feasibility study and represents a preliminary stage towards actual optical measurements with rotary blood pumps. Therefore, a test bench with facilitated optical accessibility compared to Ventricular Assist Devices as well as operating conditions are introduced. Increased attention is dedicated to evaluation of measurement data by means of choosing a suitable procedure. Therefore, commonly used 2D-histograms for LDV raw data evaluation are compared to the method of Gaussian Kernel Density Estimation (Gaussian KDE). Subsequently, pre-processed raw data is further evaluated with a specially tailored Velocity Profile Validation Algorithm and determined circumferen-tial velocity profiles are discussed. In summary, herein presented feasibility study is deemed successful and LDV Pro-file Sensor technology is capable of resolving flow topologies within small gaps as they appear in Ventricular Assist Devices. Thus, LDV Profile Sensor technology may improve development of rotary blood pumps.

A Bayesian approach for shaft centre localisation in journal bearings

It has been shown that ultrasonic techniques work well for online measuring of circumferential oil film thickness profile in journal bearings; unfortunately, they can be limited by their measuring range and unable to capture details of the film all around the bearing circumference. Attempts to model the film thickness over the full range of the bearing rely on deterministic approaches, which assume the observations to be true with absolute certainty. Unaccounted uncertainties of the film thickness may lead to a cascade of inaccurate predictions for subsequent calculations of hydrodynamic parameters. In the present work, a probabilistic framework is proposed to model the film thickness with Gaussian Processes. The results are then used to estimate the location of the bearing shaft under various operational conditions. A further step in the process involves using the newly-constructed dataset to generate likelihood maps displaying the probable location of the shaft centre, given the bearing rotational speed and applied static load. The results offer the possibility to visualise the confidence of the predictions and allow the true location to be found within an area of high probability within the bearing’s bore.

Optimization of a Lorentz forces EMAT for the reconstruction of the circumferential thickness profile of a steel pipe using high order shear horizontal modes

Corrosion is a chemical reaction affecting a wide range of materials. Safety-critical structures in the oil, gas, petrochemical, and many other industries need a fast, reliable screening technique that can be performed without operational disruption. Partially accessible structures such as pipes at supports or under a layer of insulation are particularly challenging. In this respect, high-order shear horizontal (SH) guided wave modes can be used in medium-to long-range thickness gauging thanks to their cutoff frequency-thickness product. As the wave propagates, a reduction in the thickness behaves like a low-pass filter for high-order modes. It has been demonstrated that periodic and permanent magnet electromagnetic acoustic transducers (PPM EMAT) can be used for transmission and reception. This paper presents a comparative study between different PPM EMAT configurations on a 323.8 mm diameter, 10.2 mm thick steel pipe. Finite element (FE) simulations and experimental measurements are used to compare the effectiveness of the different configurations to measure the thickness in four intervals: less than 5.4 mm, between 5.4 and 7 mm, between 7 and 8 mm, and between 8 mm and 10.2 mm, thus allowing to detect thickness losses of up to 50% of the nominal thickness of the waveguide.

Experimental and Numerical Analysis of Loss Characteristics of Cooled Transonic Nozzle Guide Vanes

Abstract This article presents high-fidelity experimental traverse measurements downstream of an annular cascade of transonic nozzle guide vanes (NGVs) from a high-pressure (HP) turbine stage. The components are heavily cooled real engine components from a modern civil gas turbine engine, operated at scaled engine conditions. Tests were conducted in the high technology readiness level (TRL) Engine Component Aerothermal (ECAT) facility at the University of Oxford. High-resolution full-area traverse measurements of local kinetic energy (KE) loss coefficient are presented in several axial planes. In particular, we present circumferential loss coefficient profiles at several radial heights, full-area traverses at three axial planes, and fully mixed-out loss calculations. The analysis of these data gives insight into particular loss structures, overall aerodynamic performance, and wake mixing rates. The effect of exit Mach number on performance is also considered. The data address a gap in the literature for the detailed analysis of traverse measurements downstream of HP NGV engine components. Experimental data are compared with steady and unsteady Reynolds-averaged Navier–Stokes (RANS) simulations, allowing benchmarking of typical computational fluid dynamics (CFD) methods for absolute loss prediction of cooled components. There is relatively limited aerodynamic performance data in the literature for heavily cooled NGVs, and this study represents one of the most comprehensive of its type.

Experimental Research on the Flow in the Steam Turbine Axial Exhaust Hood

There is the still remaining task to increase the efficiency of power plants and steam turbines. One possibility to increase the thermodynamic efficiency is to apply a suitable exhaust hood. Axial exhaust hoods are mainly designed for small turbines up to 180 MW. They are a very important part of steam turbines and its main purpose is to take away the steam from the last stage outlet to a condenser with minimal loss or even with pressure compression and an increase in the last stage enthalpy drop. This paper concerns experimental measurements on the axial exhaust hood wind tunnel model. The main goal of this paper is to determine how given geometrical and flow parameters affect the resulting pressure recovery coefficient. Main observed parameters are velocity and circumferential angle profiles at the diffuser inlet along with a number, shape and geometrical configuration of internal struts. Several geometrical variants are measured for two types of circumferential angles at the diffuser inlet and for two values of Mach number in the presented work. Multi-hole pneumatic probes and pressure taps are used for flow parameters measurement. The proposed experimental model, along with corresponding CFD (computational fluid dynamics) simulations, will help to optimize the flow parameters in the exhaust hood and allow a decrease in pressure losses in this part.