Band 41, Heft 2

Turbine inlet air temperatures are extremely high, which can result in blade material damage. As a result, cooling the turbine blades is required, and a variety of cooling techniques have been introduced. The majority of the previous research on pin fins has focused on circular fins using a wedge duct to apply a constant temperature and uniform heat flux to the end wall and pin fin surfaces. The present study compares seven oblong pin-fins to seven circular pin fins in a wedge duct with a Reynolds number range of 10,000–50,000 and a constant heat flux (surface) of 3280 W/m 2 applied to the endwall and surfaces of the oblong pin fin. The results indicate that the friction factor for oblong fins is 14% lower than for circular pin fins. The thermal performance factor is increased by 11.4%. The thermal performance factor can be improved by using oblong pin fins with higher Reynolds numbers.

Circulation control is a kind of efficient flow control technology which can improve aircraft aerodynamic performance and reduce fuel consumption. However, improving the aerodynamic efficiency of a circulation device to enhance flight endurance and achieve environmentally flying is a challenging problem for the application of circulation control. This paper presents an efficient flow control technique that combines co-flow jet and multi-stage slot circulation control. The combinational flow control technique is applied to a supersonic airfoil to test its energy consumption and aerodynamic benefit achievement. Results show that both the single and double slot circulation control can improve the maximum lift-drag ratio of the baseline airfoil, with an increment of 11.3% and 19.1%, respectively. Compared with the single application of co-flow jet control which can increase the lift-drag ratio of the baseline airfoil by 16.3% and extend the stall angle of attack from 6° to 8°, the combinational flow control can obtain a more significant lift-drag ratio increment by about 27.3% and eliminate flow separations at high angle of attack. The stall angle of attack can even be increased to about 10°. Additionally, the blowing efficiency of the circulation control airfoil has been comprehensively analyzed. The results show that the maximum effective lift-drag ratio and highest blowing efficiency can be achieved at a blowing coefficient of 0.00235.

The objective of the study is realizing the effect of fuel mass flow rate and flight speed on combustion in scramjet engine. DLR conical strut based scramjet combustor configuration was chosen and simulated the chemical reaction between the air and hydrogen fuel. A slot of size 40 mm × 0.295 mm provided at the center of the strut to injected hydrogen fuel from the rare side in to the downstream flow. ICEM CFD software is used for the generation of structured elements in computational domain for three dimensional flow analyses. Standard k-epsilon turbulence model and species transport equation is used in ANSYS fluent solver. The predicted temperature, velocity distribution along the axial length was compared with the experimental results and validated. The temperature distribution at different Mach numbers and mass flow rate reveals that the peak temperature increased with the flight speed and inlet fuel mass flow rate. The peak temperature noticed at the center of the combustor is around 3500 K at a flight speed of Mach 4. The predicted variation of temperature, pressure, velocity in the combustor and the flow structure for reacting flow facilitate good understanding of the combustion process in scramjet combustor.

With the advancement of the supersonic aero propulsion system, optimizing the combined performance of inlet/engine integration has become increasingly crucial. To solve the coupling inlet/engine problem, a quasi-one-dimensional inlet modeling and drag calculation method are proposed, integrated performance seeking control (PSC) based on the neighborhood-based speciation differential evolution-grey wolf optimizer (NSDE-GWO) is presented and quantitatively analyses the influence of variable geometry inlet regulation on performance. The results reveal that the optimization effect of the ramp angle adjustment is generally better than that of the bleed adjustment, and the NSDE-GWO hybrid algorithm achieves remarkable optimization solutions in all three different modes. The PSC with variable geometry inlet adjustment provides more additional potential for optimization compared with fixed geometry inlet, and the performance can be maximized by adjusting both the bleed adjustment and the ramp angle. This study maximizes the exploitation of potential and has theoretical guidance and practical engineering significance.

An experimental study is conducted to determine the effect of chevrons with zero penetration angles at the CD nozzle exit on an emitted noise field. The implication of passive control is to reduce the blockage of the nozzle exit area with minimal engine thrust penalty. The cold air jets issued at design Mach numbers 1.5 and 1.75 from the De Laval nozzles of the circular section were investigated. This passive control eliminates screech tones at the over and ideally expanded conditions at 60° and 90° in the azimuth plane. The acoustic data measurements have also been observed for the chosen jet Mach numbers. The schlieren images reveal the shock cell pattern to eliminate the effect of shock-associated noise levels at supersonic jets. The results show that 10 chevrons with no penetration act as an effective eliminator of screech tone and noise suppression average ∆OASPL value up to 3 dB at Mach number 1.75.

The entire compression system of DGEN380 was selected to study the degradation of aerodynamic characteristics caused by erosion of the leading edge. Numerical simulations under different degrees of leading edge erosion were performed. It was found that the leading edge erosion causes a significant decrease in operability from 70 % of the blade height to the tip, and mainly affects the subsequent flow field in the bypass. At 90 % of blade height, the isentropic efficiency and total pressure ratio of the blade with leading edge erosion are reduced compared to the origin blade. Afterwards, the thrust equation was introduced to analyze the effect of leading edge erosion on the thrust loss under different operating conditions of the aircraft. Among the three operating conditions, the thrust loss rate of the cruise condition was the largest, which provided a reference for the subsequent evaluation of the blade repair condition.

Film and jet impingement cooling are widely used techniques in gas turbine vane and blade cooling. The present work investigates and compares the flow structure of a film-cooled flat plate with a hybrid cooling scheme. The hybrid cooling scheme combines both impingement hole and film holes and is named combined impingement-film (IFC) cooling. Experimental validation and computational analyses are carried out on a flat plate with film holes. Different flow parameters, such as velocity pattern, Turbulent kinetic energy, and streamline flow structure, are compared for the two cases in different regions of the flat plate. It is observed that the hybrid scheme shows advantages over film cooling. The jet-to-jet interaction, jet crossflow interaction, and vortex formation are the main factors affecting film cooling performance. There is a 52 % drop in turbulent kinetic energy for the hybrid cooling compared to the film cooling at the film hole exit. More mixing in the coolant and mainstream interaction is observed for the FC case than in the IFC.

Rotating machinery, such as turbo-jet engines, operate at a high rotational speed and passes through critical zones. The dynamic response of high-speed machines is critical for long-term stability and functioning. In this work, a fast and effective method for detecting coupling misalignment utilising time-frequency analysis (TFA) based on both the adaptive noise added complete ensemble empirical mode decomposition and wavelet-based denoising is presented. This novel and innovative method detect the coupling misalignment feature via the amplitude modulation aspect in the envelope analysis of the fault-containing intrinsic mode function. The Hilbert spectrum analysis provides spontaneous frequency and spectral energy in the time-frequency domain. The experiments were performed for various rotor accelerations and combined parallel and angular coupling misalignments using a laboratory test rig. The suggested approach gives excellent denoising efficiency and can improve misalignment identification accuracy. Additionally, it may be highly helpful for machinery that starts and stops often.

Effect of free boundary on the flow field characteristics of a single expansion nozzle has been studied experimentally and computationally. The single expansion nozzles studied in this investigation are a convergent-divergent nozzle of rectangular cross-section with convergent-divergent wall on one side and a flat wall on the opposite side, and an identical convergent-divergent ramp with its top open to atmosphere. The studies have been carried out at nozzle pressure ratios 2, 3, 4 and 5. The results show that the single expansion nozzle with wall boundary is able to deliver the flow with Mach number around 1.5, at nozzle pressure ratios of 4 and 5 even with the single expansion. The nozzle with free boundary, the wall static pressure is appreciably lower than that of nozzle with closed boundary and the exit Mach number is 1.5 for NPR 4 and 1.75 for NPR 5. That is, at the exit, the single expansion nozzle with free boundary delivers higher Mach number compared to single expansion nozzle with wall boundary for NPR 5.

In this work, a combined design of blade and endwall using the Extended Free Form Deformation technique is proposed and implemented on a transonic compressor rotor (the NASA Rotor 67). The best combined design is explored by numerical investigations and optimization via Kriging surrogate model method. As a result, by only modifying the hub and blade under 15 % span, the peak adiabatic efficiency is increased by 0.4 % and the overall aerodynamic performance for all operating conditions is also improved. An analysis shows that the enlarged dihedral angle between the hub and blade restrains boundary layer intersection and development. Meanwhile, the optimized hub changes the pressure distribution and prevents migration of cross-flow. As a result, the low-energy flow in the corner is accelerated downstream and the separation is limited, leading to an effective improvement in throughflow capability and aerodynamic performance in the corner region.

To reveal the influence of distortion of S-duct on the flow field and performance of transonic fan, full annulus unsteady numerical simulation was carried out under S-duct/fan integrated condition. This study focuses on the coupling flow of S-duct/fan integrated condition under peak efficiency (PE) condition and near stall (NS) condition. Results show that, compared with the condition that S-duct or fan is investigated alone, the distortion of S-duct is suppressed under S-duct/fan integrated condition. The curved structure of S-duct is the important reason for the flow migration from undistorted region to distortion region. Higher inlet relative Mach number and more work input of the rotor are observed in the counter-swirl region. The flow separation in S-duct is weakened under NS condition compared with that of PE condition. Counter-swirl region of blade tip has larger region of blockage, and rotating stall inception is most likely to occur in this region.

In order to improve the real-time performance of the aero-engine Component-Level Model (CLM) while ensuring accuracy, a method for the Calculation of Thermodynamic Parameters of Working Fluids (CTPWF) based on a Neural Network and Newton Raphson (NN-NR) is proposed. In this method, the enthalpy or entropy under different fuel-air ratio and humidity conditions is mapped to temperature by a neural network, and the mapping output is used as the initial solution of Newton Raphson (NR) iteration. Then, a high-precision solution can be obtained through a few iterations, which avoids the shortcoming that the traditional method uses a fixed initial solution that leads to too many iterative steps. This effectively reduces the number of iterative steps and improves the calculation efficiency. This method is applied to the aero-thermodynamic calculation of each component of an engine CLM, which improves the accuracy and real-time performance of the CLM. The simulation results show that, compared to the traditional method, the proposed method improves the accuracy of the CTPWF and can reduces the single aero-thermodynamic calculation time by 25 % when humidity is not considered and by 47 % when humidity is considered. This effectively improves the real-time performance of the CLM.

The temperature distribution and thermal Stresses induced by a temperature difference for steady state heat transfer in silicon carbide (SiC) ceramic tube heat exchanger with circular fins was computationally simulated by a finite element method and probabilistically evaluated in view of the several uncertainties in the performance parameters. Cumulative distribution functions and sensitivity factors were computed for the hoop stresses due to the structural and thermodynamic random variables. These results are used to identify the most critical design variables in order to optimize the design and make it cost effective. The probabilistic analysis leads to the selection of the appropriate measurements to be used in structural and heat transfer analysis and to the identification of both the most critical measurements and parameters.

To reduce excessive vibration of a turboprop engine with qualified balanced compressor and turbine rotor, the finite element model of the rotor system was established. The magnitude, axial distribution and especially the phase combinations of the residual unbalances were considered and optimized. Based on the numerical results, the whole engine tests were conducted for verification. The numerical and experimental results show that the vibration level of the rotor system can be significantly reduced by only changing the phase combination of the residual unbalances. The magnitude, axial distribution of residual unbalance and rotational speed of the rotor play a very important role in determining the optimal phase combination. The optimal phase combination under different rotational speeds might be conflicting, and reasonably designed optimization would be a feasible solution. The findings of the research can provide important reference for the design and troubleshooting for similar industrial turbine engines.

For an aero turbo-shaft engine, rain water enters the intake protection device and the morphology of water droplets after hitting the wall will affect the internal flow of the compressor. In this paper, Sommerfeld number was used to determine the shape of water droplets after they hit the wall. The flow field and characteristics of the compressor with inlet particle separator under different water ingestion conditions were studied with considering the impact of water film and droplets splashing near the wall. The results show that the entry of water droplets deteriorates the internal flow field of the compression component, and the water film affects the flow state of the airflow near the wall. Compared to the effect of the splashing factor, the viscous resistance effect of water film near the wall on the airflow and boundary layer can cause a significant reduction in the characteristics and stability of the compressor.

The significance of the volume effect on the compressor performance during acceleration and deceleration has received limited attention, despite its demonstrated importance in compressor flow instabilities. To better understand this effect, the in-house simulation program CAM (a modular transient simulator) is used to investigate the volume effect on the compressor transient performance. The modeling procedure is derived from Greziter’s lumped parameter approach and the accuracy of the simulation model is verified by experimental data. This study presents a comprehensive comparison and explanation of variations in compressor transient behavior observed under different conditions, including different shaft speed change rates, compressor volume sizes, and operating speeds. The relative difference between the compressor inlet and outlet mass flow is identified as the key factor contributing to these discrepancies. In addition, a simplified analytical model is developed to provide a basic description of the compressor operating line during acceleration and deceleration, which also provides additional support for the validity of the numerical results. This study systematically establishes the dynamic dependencies between shaft speed change, pressure and mass flow change, offering critical information for ensuring the safety of compressors during transient operation.

This study measured the aerodynamic performance and dynamic pressure signals of a compressor cascade platform with high-speed rotating endwall. Instead of translational movement, the endwall features an innovative large rotating disk. Measurements were conducted on a controlled diffusion airfoil (CDA) under different conditions: tip clearances (3 mm and 2.5 mm), inlet incidences (+6° and −6°), and stationary or high-speed rotating states at 0.5 Ma inflow. The results reveal that endwall movement amplifies circumferential leakage losses, increases kinetic energy, deviates the leakage flow path, and reduces total pressure loss in the leakage core region. Dynamic pressure results reveal greater unsteadiness in the tip region under positive incidence conditions and with larger clearances. Characteristic frequency ranges (8000 Hz for system vibration and 150∼200 Hz for leakage flow development) are identified. Further experimental measurements and high-precision simulations are needed the determine the matching relationship between complex flow behaviour in the blade tip region and characteristic frequency.

Hydrogen-blended fuel is a promising resource for future generations of gas turbine engines, due to its capability of reducing carbon-based emissions. This paper presents a numerical study to assess hydrogen-enriched combustion in a laboratory-scale burner operating at a high turbulence level and under lean and stoichiometric burning conditions. Moreover, a wide range of H 2 (up to 90 %) is used for enriching CH 4 -air combustion in combination with two different swirl levels. The results show that a high swirl intensity results in shorter flames, due to the increased turbulent intensity, which reduces the flame surface area and uniformness the reacting zone. Besides, increasing swirl intensity further increase flame temperature for a given H 2 -blended fuel. Overall, the results suggest that high swirl intensity in combination to lean mixtures is favorable when using H 2 -blended fuel with high H 2 concentrations. The simulation results also demonstrate that considering radiation heat loss is influential, as it yields a reduction of the outlet temperature by not less than 100 K, bringing down NO x emissions by half.

This article delves into the intricate relationship between the modeling parameters of an axial supersonic through-flow fan (STFF) rotor and its performance based on an active subspace method. It considers the influence of the STFF rotor key parameters on its performance. Implementing the active subspace method generates cloud maps to visualize the performance of the STFF rotor. Moreover, this study investigates the correlation between Bezier curve variables for constructing blade angles and critical performance metrics, such as the total pressure ratio and isentropic efficiency. After a 50 % chord length, the Bezier control point parameters dominate the effect on the total pressure ratio with a linear relationship. This article provides comparative flow field analyses on the blade elements with different performances under three working conditions. Under the constraint of the blade chamber turning angle, there is a linear relationship between the upper and lower limits of the isentropic efficiency distribution and total pressure ratio. This study shows that the total pressure ratio, installation angle, and maximum deflection value are positively associated. Further analysis provides an empirical formula.

Aero engine performance analysis is very important for engines under development as well as for engines in service for condition monitoring. Predictions of aero engine performance and ability of building the simulation model is an invaluable asset for designers, manufacturer and end-use operator. This paper presents the methodology in establishing the baseline performance of a twin spool mixed flow low bypass turbofan engine through extensive testing at engine test bench. The baseline data is used to validate a GasTurb model which is subsequently used for assessment of off-design performance and component degradation responsible for performance deterioration at various service hours. The estimated exhaust gas temperatures by the model for degraded engines are in good agreement with the measured data. The model further assesses the drop in HP compressor efficiency and shift in operating line which will be very useful for taking judicious decision for withdrawal of engines and is expected to reduce or delay withdrawals and increase the availability of engines at operating base.

In variable geometry turbine vanes, tip clearance height and shape vary with the rotation of the vane, which affect the aerodynamic performance significantly. However, these issues are rarely considered in published studies. The current paper investigated the flow field features of transonic variable geometry turbine vanes with non-uniform partial clearance induced by the vane rotating. The results show that: The influence of guide vane rotation on the clearance height and its distribution cannot be ignored. At the same turning angle, the maximum clearance difference is up to 0.79 mm (0.8 % vane height). The height and shape variation of the non-uniform clearance leads to the change in the leakage flow rate, secondary flow structure, and aerodynamic loss of the variable guide vane. Under the combined effect of pressure difference on both sides of the clearance, axial and circumferential non-uniformity of clearance height, the total pressure loss coefficient is up to 9.44 % when the turning angle is −10°. The effect of the pivot on the clearance flow was also analyzed. The pivot increases the pressure in the gap flow field and reduces leakage flow velocity. However, a backflow region appears at the suction side of the pivot, which increases the aerodynamic losses.