bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Pressure Gradient on Flame-Vortex Interaction and Flame Stability
Authors: Yalcinkaya Yagiz , Bozkurt Ogeday E. , Gungor Ayse G. 
Published: October 2022

Abstract
This study presents numerical investigations of turbulent premixed bluff-body stabilized flame by emphasizing the influence of pressure gradient on flame-vortex interaction and flame stability for lean combustion applications. Large eddy simulations of four different geometrical configurations, diffuser 3°, diffuser 1.5°, nominal, and nozzle that resulted in mild to strong pressure gradients are presented. Numerical investigations allowed determining the effects of geometry-induced pressure gradient on the flame structure, development of the flame-front vorticity and turbulent structures and flame stabilization. It is shown that the pressure gradient plays a key role for the spatial and temporal development of the flame front vorticity and baroclinic torque. The flow deceleration in diffuser geometries suppresses the flame-induced vorticity mechanisms, which in turn lead to large wrinkle forms of the flame and may lead to local extinctions along the flame front. The favorable pressure gradient in the nozzle geometry, on the contrary, increases the baroclinic torque that restrains the development of the shear layer vorticity and hence prevents local extinctions.
Profile Loss Reduction of High Lift Turbine Blades With Rough and Ribbed Surfaces
Authors: Ananth S. M. , Nardini Massimiliano , Vaid Aditya , Sandberg Richard D. , Vadlamani Nagabhushana Rao 
Published: October 2022

Abstract
Low pressure turbines (LPT) typically operate at low Reynolds numbers, of O(105), resulting in transitional boundary layers on the suction surface. These boundary layers are prone to separation under the strong local adverse pressure gradients on the aft portion of the blade. Intermittent free-stream turbulence, periodic wakes shed by the upstream blades and surface roughness due to gradual degradation of the blades have been shown to suppress the separation bubble on the suction surface of the LPT blade. Although this generally leads to a profile loss reduction, some of the benefit is offset by a loss increase associated with a larger turbulent wetted area. In this work, we explore a strategy where the losses in both the transitional and turbulent boundary layers can be reduced. In particular, we employ surface roughness in the transitional regime to trip the boundary layer and reduce the separation bubble related losses. Subsequently, we explore the possibility of utilizing riblets in the turbulent regime to further reduce the losses due to the turbulent wetted area. To investigate the efficacy of this ‘rough-riblet blade surface’, high fidelity eddy-resolving simulations are carried out on the configuration of a flat surface subjected to streamwise varying pressure gradients. A contoured upper wall is used to mimic the pressure distribution typically encountered on the suction surface of a high lift turbine blade. The Boundary Data Immersion Method is used to represent different riblet shapes and roughness elements, while a digital filtering approach is used to impose free-stream turbulence at the inlet. The influence of different riblet geometries on skin friction drag of transitional and turbulent boundary layers under streamwise varying pressure gradients are discussed in detail. The effect of different riblet shapes in conjunction with the roughness elements on the passage losses is shown through boundary layer integral parameters and Reynolds stresses.
An Experimental Test Case for Transonic Low-Pressure Turbines - Part 2: Cascade Aerodynamics at On- and Off-Design Reynolds and Mach Numbers
Authors: Lopes G. , Simonassi L. , Torre A. F. M. , Patinios M. , Lavagnoli S. 
Published: October 2022

Abstract
In this two-part paper, a novel test-case for transonic low-pressure turbines (LPT) is presented. The current study is a comprehensive report on the design, commissioning and testing of a high-speed LPT cascade. Part II reports the characterization of the aerodynamics at on- and off-design flow conditions.
A detailed analysis of the steady aerodynamics of the highspeed low-pressure turbine blade is presented for a range of engine representative outlet Mach numbers from 0.70 to 0.95 and Reynolds numbers from 65,000 to 120,000. The blade 3D aerodynamics are characterized using an innovative set of traversable blades, enabling high-resolution radial measurements. A novel method to estimate the location of separation-reattachment based on pneumatic tap measurements is presented. The separation on the blade suction side is strongly influenced by the Reynolds number at the lower Mach numbers, while open separations were observed at transonic exit conditions independently on the Reynolds number.
Downstream measurements by means of a five-hole probe, and pressure taps located in the passage endwall are employed to study the secondary flow development and structures at the cascade outlet. The results show that the losses follow different trends at high and low Reynolds numbers. The profile losses at Re = 70k decrease with increasing Mach number, contrary to what is observed for Re = 120k. The minimum secondary flow losses are found for an off-design condition with lower Mach number with respect to the nominal. The off-design comparisons presented in this paper indicate that at low Reynolds, operating at transonic outlet Mach numbers leads to beneficial effects on the performance.
Potential and Evolution of Miniatures Compressed Air Energy Storage Plants Based on Impulse Turbine
Authors: Al Jubori Ayad M. , Al-Sadawi Laith A. , Biedermann Till , Alfarawi Suliman 
Published: October 2022

Abstract
This paper describes the work carried out to develop an impulse turbine for miniatures compressed air system. This study hypothesizes the question; what is the effect of combining an impulse turbine loss model into a compressed air energy storage system analysis? The miniatures power system has lower mass flow rates which lead to a small turbine size. The miniature impulse turbine has relatively low efficiency and is highly sensitive to operating conditions at a low mass flow rate due to all losses in terms of passage, trailing edge, incidence, and clearance becoming higher amounts compared to the total losses of the percentage foundation.
The development of a novel impulse turbine configuration is presented based on one-dimensional design and three-dimensional simulations. The impulse turbine in single-stage configuration was designed and analyzed for a range of operating conditions in terms of pressures, temperatures, mass flow rate, and rotational speeds. The simulations results showed that the maximum efficiency and power were 65.93% and 4.019 kW respectively with a mass flow rate of 0.2 kg/s. The energy analysis revealed that the system efficiency was 10.3%. The miniature compressed air energy storage system driven by an impulse turbine can be used to generate electricity for small power applications.
High Pressure Testing With Optical Diagnostics of a Hydrogen Retrofit Solution to Eliminate Carbon Emissions
Authors: Koomen Joris , Dammers Tim , Demougeot Nicolas , Stuttaford Peter , Heinze Johannes , Stockhausen Guido , Fleing Christian 
Published: October 2022

Abstract
Ensuring grid stability is becoming an increasingly large challenge as the amounts of power from new highly fluctuating sources like solar and wind are increasing. Fuel flexible gas turbines which can run on carbon free or low carbon fuels offer grid stability both on the basis of their inertia and the possibility to quickly ramp-up and down.
A consortium led by Thomassen Energy is at work at realizing a cost-effective, ultra-low emissions (sub 9ppm NOx and CO) combustion system for gas turbines in the 1–300 MW output range. A key requirement is fuel flexibility and stable operation from 100% natural gas to 100% hydrogen and any mixture thereof.
This paper describes the results of the second step in the testing cycle of the developed combustion technology. In this step the FlameSheet™ is validated at machine operating conditions. The tests are completed using a state-of-the-art test setup combined with novel optical analysis techniques.
The results show that one of the developed hardware variants can run on a wide range of fuel compositions up to 100% hydrogen without flashback while emissions are below 9 ppm at 15% O2 dry conditions.
Computational and Experimental Study of Film-Cooling Effectiveness With and Without Downstream Vortex Generators
Authors: Lee Chien-Shing , Shih Tom I-P. , Straub Douglas , Weber Justin , Robey Edward 
Published: October 2022

Abstract
Downstream vortex generators that involve a pair of rectangular plates arranged in an open V shape placed just downstream of each film-cooling hole was shown to create flow and vortical structures that entrain lifted film-cooling flow back to the surface and increase its lateral spreading on the surface (GT2020-14317). In this study, computations and measurements were performed to examine the flow mechanisms this vortex generator induces to improve film-cooling effectiveness of a flat plate with the cooling flow emanating from one row of inclined holes. Parameters studied include blowing ratio (BR = 0.75, and 1.0) and temperature ratio (TR = 1.07 and 1.9). The computational study is based on steady RANS closed by the shear-stress transport (SST) turbulence model with and without conjugate analysis. The experimental study was conducted by using a conjugate heat transfer test rig with a plenum, where cooling flow is introduced. Measurements made include velocity and temperature profiles upstream and downstream of the film-cooling holes as well as temperature at several locations on the hot and cold sides of the film-cooled-flat plate. The computational study was validated by comparing computed results with those from measurements at BR = 0.75 and 1.0 and TR = 1.9. Computational and experimental results are presented to show the effects of BR and TR on the flow structures and how those structures improve the effectiveness of film cooling with and without the downstream vortex generators and with and without conjugate heat transfer.
Upgrades to the Single Stage Axial Compressor and Fan Facility for Low Pressure Ratio and Boundary Layer Ingesting Fan Research
Authors: Stephens Julia E. , Hughes Chris 
Published: October 2022

Abstract
Next generation aircraft engine efficiency goals will be met through high bypass ratio engines. To achieve these goals, a combination of small core and low pressure ratio fan technologies will be necessary. Additionally, advanced propulsion airframe integration concepts, such as boundary layer propulsion, and distributed electrically driven fans with short inlets or wing integration strategies, are beginning to be investigated for their potential fuel burn savings.
In order to realize the potential fuel savings from these technologies, it is necessary to have testing capabilities for the components. The NASA Glenn Research Center (GRC) Single Stage Axial Fan and Compressor Facility (also called the GRC W-8 Facility) has recently undergone several significant upgrades in order to effectively test low pressure ratio fans and various inlet distortions. This paper will outline various challenges to testing low pressure ratio fans and the methods implemented to ensure that the W-8 facility is capable of performing these tests and acquiring high quality data. The upgrades include significant piping upgrades to reduce pressure loss and turbulence, capability for inlet total pressure and swirl distortion, increased test section length including a longer shaft, a two component balance, an upgraded rotating data system, and a new temperature characterization to reduce uncertainties in thermocouple measurements.
Experimental Study on Heat Transfer in a Rotating, Ribbed Serpentine Cooling Channel With Bleed Holes
Authors: Zhu Chenghua , Wen Jie , Xu Guoqiang , Chen Yanan 
Published: October 2022

Abstract
The effect of rotation on heat transfer in a typical turbine blade middle-chord channel is experimentally investigated. The channel is characterized by ribs, three-pass serpentine passages and bleed holes. Cooling air is radial outward in the first passage and the third passage, and is radial inward in the second passage. The bleed holes were placed on trailing side (pressure side) of the first passage and the second passage, and on both trailing side and leading side (suction side) of the third passage. An additional small stream of cooling air is injected at the second 180-deg hub turn to compensate the insufficient cooling flow rate in the third passage. The major inlet Reynolds number (based on the inlet of the first passage inlet) and rotation number are varied from 17000 to 33000 and 0 to 0.43, respectively. Besides, the mass flow rate ratio (MR, the mass flow rate of second stream to the major coolant) is varied from 0 to 0.2. The wall temperatures were measured by thermocouples embedded behind the copper plates to obtain the regional average heat transfer coefficients. The result shows that compared with the traditional square U duct, the rotation effect on heat transfer is apparently suppressed in current channel with more realistic blade configurations. According to the experimental data, the overall averaged heat transfer in the first and second passage are respectively weakened by 6.2% and 2.4%. Under the influence of the second stream, rotation elevates heat transfer in the third passage, whereas a heat transfer reduction is observed in the second passage with ascending MR, indicating that high MR case (MR = 0.2) is not recommended whether from saving cooling air or improving the general heat transfer of the cooling channel.
Leakage Flow Impact on Shrouded Stator Cavity Flow Topology and Associated High Speed Axial Compressor Stage Performance
Authors: Babin Cedric , Ottavy Xavier , Fontaneto Fabrizio 
Published: October 2022

Abstract
This paper presents the investigation of realistic cavity leakage flow for the von Karman Institute for Fluid Dynamics H25 axial compressor stage, equipped with a shroud cavity of average Reynolds number Rer = 2.2 * 106 and average aspect ratio G = 0.06. On top of overall performance measurements, time averaged data from unprecedented experimental dataset are used to characterize the stator hub shroud cavity flow field and its interaction with the power stream. The sensitivity of the stage performance and stability as well as the cavity flow topology is evaluated against injection conditions, compressor throttling and compressor speed. Parametric steady RANS simulations of the stage under injection are used to support the findings and state on the relevance of such approach in the preliminary design phase of axial compressor components.
As an example, a stage efficiency reduction of 0.97% for a leakage fraction of 0.56% at design point is retrieved. This performance drop is attributed to the effect of cavity flow on: the blockage ratio, the boundary layer skewness, and total temperature increase at stator row inlet. It is also presented that there is a mutual interaction between the cavity geometry and the cavity flow field organization. The injection homogenizes the cavity flow field and the associated pressure gradient. The various operating conditions presented also demonstrate that the cavity flow studied is, on average (i.e. time), sensitive to changes in compressor rotation speed and changes in stage loading.
A GTC-CGC Health Assessment Method for Gas Turbine Engine
Authors: Ao Ran , Cao Yunpeng , Luan Junqi , Han Xiaoyu , Li Shuying , Yan Li 
Published: October 2022

Abstract
Due to wear, fouling, corrosion, and other factors performance degradation of compressor and turbine seriously affects the health state of gas turbine engines. However, the health status of gas turbine engines is inconsistent under the variances of the external environment and operating load, which brings great challenges to health assessment and remaining useful life predictions. To solve this problem, a grey target calculation and cloud gravity center (GTC-CGC) health assessment method is proposed. The three-dimensional data normalization process is to characterize the different initial states between samples. The empirical signal-to-noise ratio and entropy weight are used to calculate the subjective and objective weights of health indicators, and convex optimization is used to realize the fusion assessment. A health assessment model was established by the sliding time window to track and calculate the real-time health state of the gas turbine engine. Finally, health assessment and remaining useful life prediction tests were conducted on turbofan engines using the NASA C-MAPSS dataset. The experimental results show that compared with the self-organizing neural network, the monotonicity, robustness, and trend of the health assessment results were improved by 0.3216, 0.0843, and 0.0355 respectively; Based on the GTC-CGC health assessment results, a third-order linear regression algorithm was used for turbofan engines remaining useful life prediction, the prediction score is 265, and root mean squared error is 26.1542, which is equivalent to the prediction accuracy of mainstream intelligent prediction methods such as convolutional neural network and short-term memory neural network.
Response of Separated Boundary Layers to Steady and Pulsated Flow Injection in Transonic Internal Flows
Authors: Nowak Hunter D. , Lluesma-Rodriguez Federico , Rahbari Iman , Clark John P. , Paniagua Guillermo 
Published: October 2022

Abstract
A new class of power generation devices that experiences increased losses due to bulk flow separation in segments of their expected in-flight regime is emerging. As such, active flow control becomes increasingly relevant to mitigate these losses and reclaim the entire flight envelope. This study explores the effect of flow injection on transonic flows experiencing bulk separation. Reynolds-Averaged Navier-Stokes simulations of a 3D wall-mounted hump at low Reynolds numbers are conducted to assess the response of transonic bulk separation to flow injection. Unsteady simulations are performed to understand the differences between slot and discrete port injection and determine optimum forcing frequencies. Discrete ports require higher pressures to overcome the momentum deficit associated with the smaller injection area relative to the width of the domain. Steady and unsteady injection are found as viable strategies in mitigating the extent (or appearance) of bulk separation. Experiments are conducted with discrete injection for a range of Mach and Reynolds numbers. The response of the bulk separation to said injection is evaluated by analyzing both local pressure measurements and schlieren imaging. The study shows that the required pressure of injection is strongly correlated to the length scale of the uncontrolled separation. With Large Eddy Simulations, the flow separation and frequency content within the separated region can be reasonably predicted. This study aims to take further steps to establish guidelines for applying flow control to the emerging class of power generation devices experiencing losses from bulk separation.
On the Influence of Stator-Rotor Radial Gap Size on the Fluid-Dynamic Performance of Mini-ORC Supersonic Turbines
Authors: Cappiello Alessandro , Majer Matteo , Tuccillo Raffaele , Pini Matteo 
Published: October 2022

Abstract
Radial-Inflow Turbines are considered the most suited expanders for waste heat recovery via high-temperature mini-organic Rankine Cycle (ORC) turbogenerators thanks to high compactness, large expansion ratio handled by a single stage, and comparatively low weight. Reaching high efficiency in these machines is however a formidable challenge, as they are bounded to operate with expansion ratios exceeding 40.
Although scarcely investigated in the published literature, the size of the stator-rotor radial gap is a key design parameter as it has a large influence on fluid-dynamic performance, manufacturing, and mechanical integrity. In addition, the working conditions of the turbine are such that the stator operates with highly supersonic flows in the non-ideal thermodynamic regime, making the flow pattern in stator-rotor radial gap, which can be regarded as an area-decreasing channel, very complex. Under these conditions, the radial gap size could impact the stage efficiency up to few percentage points. The paper presents a study aimed at investigating the impact of variable radial gap on the fluid-dynamic performance of radial-inflow turbines for high-temperature mini-ORC power systems. The reference turbine is a supersonic machine for laboratory experiments under realization at Delft University of Technology, referred to as ORCHID turbine. First, a theoretical analysis is carried out to identify the relevant non-dimensional parameters governing the flow physics in the gap. Then, the effect of the radial gap size on the fluid-dynamic performance of the ORCHID turbine is assessed by means of RANS and uRANS computations. The results show that the change in radial gap size leads to a redistribution of expansion ratio between vaned and vaneless part of stationary component via a substantial change of the stator trailing edge flow structures, which, in turn strongly affects stator loss and stage efficiency, leading to 8% points reduction.
Predicting Separated Flow in a Three-Dimensional Prediffuser for Combustor Applications Using Improved Numerical Techniques and Workflow
Authors: Norman Adam , Arguinzoni Carlo 
Published: October 2022

Abstract
After the last stage of the high-pressure compressor of gas turbine engines, swirling air enters a prediffuser which attempts to straighten out the flow and convert the dynamic pressure to a static pressure. Before the combustion chamber there is an aerodynamic cowl that, typically, separates the air into three parts. The main path leads to the combustor and supplies air to the fuel nozzles, while the secondary paths branch to the inner and outer diameter shroud passages to be used for cooling processes.
Numerical tools are widely used in prediffuser design to find the optimum design that converts a large portion of the dynamic pressure to static pressure, with the target to avoid separation. Typical analysis today for combustor aerodynamics are done with large eddy simulations (LES), but for the prediffuser design most of the analysis are done using a Reynold’s average Navier Stokes (RANS) approach.
The combustor aerodynamic community today, rely on hand-crafted, structured, hexahedral meshes to solve flows inside the prediffuser. Creating a structured mesh can be very time consuming and could delay design evolution depending on the complexity of the prediffuser. Due to the flow complexity at the exit of the prediffuser and the impact that could have on flow split predictions provided to the combustor, Reynold’s stress turbulence models (RSM) are typically used. The combined effort of creating structured meshes, with the difficulty in converging results with RSM can negatively impact design times.
The effort presented here investigates modeling a true three-dimensional diffuser from Cherry et al. using a Poly-Hexcore mesh topology and the Generalized k-Omega (GEKO) turbulence model. The unstructured Poly-Hexcore meshing workflow does not require any manual meshing operations, utilizes parallel meshing, and can be fully automated to simplify the mesh generation process. The GEKO turbulence model has the flexibility to cover a wide range of flows using free coefficients and can be setup to allow robust capturing of prediffuser flow characteristics. Numerical results are compared to experimental data gathered by Cherry et al. and current numerical best practices.