Air Mass Flow Research Articles

A novel dual-wheel air-conditioning system operating strategy in different seasons

The application of solid desiccant air-conditioning systems can significantly reduce building energy consumption. Previous studies have focused on innovating the integration of solid desiccant air-conditioning systems (DACS) to improve dehumidification performance in summer. In this paper, a novel DACS is proposed, which can humidify the supply air in winter based on satisfying the dehumidification demands in summer. It can satisfy the year-round humidity requirements of domestic housing with significant savings in humidification costs. Furthermore, the operating strategy of the novel DACS is proposed, particularly for winter humidification conditions. It is adaptable as well as cost-effective compared to traditional operating strategies. The dehumidification/humidification capacity of the core component, polymer desiccant wheel, and the variation of temperature rise/temperature drop are investigated under different variations of parameters, including air temperature, air humidity, air volume flow rate, and wheel speed. The results show that with the increase of supply air mass flow from 0.6 kg/s to 1.9 kg/s, the power consumption of the system only increases by 9.5 kW. In winter, when the supply air temperature decreases from 8 °C to 1 °C, the power consumption increases by 7.2 kW, but in summer, when the temperature of the supply air increases by 7 °C, the power consumption of the system decreases by 7.0 kW. The power consumption of the system varies greatly when the humidity of the supply air is less than 17 g/kg, conversely, the power consumption of the system showed a negative trend. The analysis demonstrates the effective performance of the proposed system under varying climatic conditions.

Experimental Study of the Effect of Porous Media on the Performance of Single-Pass Solar Air Heater

Solar energy is harnessed to heat the air, which is then utilised for warming greenhouses and drying crops. Solar air heaters may readily increase their performance using an absorbent plate design with a front pass of steel wools. This kind of SAH has been investigated and compared to a conventional flat absorbent plate. Steel wool, a cost-effective and permeable substance, possesses excellent heat conductivity, and it can be utilised in ongoing initiatives to enhance convection and thermal efficiency. The analysis in this research is based on data from experiments, focusing on the single-pass SAH technique and considering two scenarios: traditional system and porous system, with air mass flow rates of 0.015 Kg/s and 0.035 Kg/s. The experimental findings show that employing porous materials increases the exhaust temp by 12.28% and 21.32 % form of air 0.015 and 0.035 Kg/s, respectively. Moreover, the solar radiation readings for non-porous and porous medium SAHs were recorded as 905.32-912.92 and 979.04-945.6 W/m2, respectively, at 1:30 p.m. Furthermore, thermal efficiency is between 33.29 % and 64.36 % in the porous scenarios and between 30.12% and 57.36% for non-porous cases. Porous media increases the thermal efficiency by 10 % and mass flow rate by 14 %.

Solar air heater energy and exergy enhancement using a v-corrugated wire mesh absorber: An experimental comparison

In this paper, the energy and exergy performance of a double-pass solar air heater (SAH) using a novel model of a v-corrugated wire mesh absorber (CM-SAH) is investigated experimentally. The v-corrugated wires are adjacent to each other in one layer along the airflow direction to reduce the hydraulic resistance. Simultaneously, this arrangement increases the surface absorptance rate of solar radiation and expands the heat exchange area. To evaluate the performance of CM-SAH, a standard SAH having a v-corrugated absorber plate (CP-SAH) and the same configuration dimensions is compared with CM-SAH. The comparison is achieved under the same operating conditions and using different air mass flow rates of (0.01, 0.02, and 0.03 kg/s). The results show that the CM-SAH outperformed the CP-SAH in terms of thermal efficiency, exergy efficiency, and output air temperature. The maximum thermal efficiencies reach 87.3 % and 65.1 %, while the maximum exergy efficiencies reach 4.4 % and 3.4 %, for CM-SAH and CP-SAH, respectively. In addition, the thermal efficiency of CP-SAH decreased after midday while that of CM-SAH continuously increased.

An approach of analyzing gas and biomass combustion: Positioned of flame stability and pollutant reduction

Biomass, as a renewable energy source, has gained attention as a sustainable alternative to conventional fuels due to its global availability and usability in rural areas. However, biomass combustion presents challenges such as flame instability and pollutant emissions. This study compares the use of methane gas, wood shavings, and a combination of these two fuels, examining the effects of preheating and flame stability in the combustion of natural gas, biomass, and their co-firing using numerical methods. An equivalence ratio of 1 has been used to avoid a rich-fuel mixture, and an air mass flow rate of 0.0001 kg/s are considered to ensures a sufficient supply of oxygen for the combustion process. Biomass fuel particles are injected from the surface of the fuel and its particle diameter ranging between 5 and 10 μm. The results showed that using the combined fuel not only increased the flame temperature at the beginning of the combustion chamber but also achieved more complete and stable combustion, with over 97 % of the fuel consumed at the start of combustion. As a result of this complete combustion, the emissions of toxic gases CO and NOx in the combustion products reached zero. Additionally, preheating the air increased the flame temperature by 14 %, while preheating the fuel reduced NOx emissions by 24 %.

Effects of motive flow temperature on holding steam ejector Performance under Condenser temperature change by considering Entropy generation and Non-equilibrium condensation

The condenser plays a crucial role as one of the key components in a power plant, directly influencing its overall efficiency. Any alteration in the power plant’s efficiency has a substantial impact on both energy consumption and the environment. The holding steam ejector (HSE) is essential for condenser operation by creating a vacuum and effectively removing air. The primary objective of this study is to evaluation the motive flow temperature (MFT) by considering various parameters such as steam price, production entropy, air suction, and entrainment ratio (ER). The investigation focuses on different temperatures within the power plant condenser. The study examines the changes in MFT within the range of 350 ˚C to 400 ˚C, as well as the variation in condenser temperature (CDT) spanning from 47 ˚C to 67 ˚C. The results demonstrate that varying the MFT impacts the functional parameters of the HSE. As the MFT increases, there is an increasing trend in the ER. Simultaneously, there is a decreasing trend observed in the cost of steam production, production entropy, and air suction. When the MFT increased from 350 ˚C to 400 ˚C, the suction air mass flow rate for temperatures of 47 ˚C, 57 ˚C and 67 ˚C decreases by 2.22%, 2.09% and 1.99%, respectively. These results highlight the influence of temperature on various parameters, showcasing how adjustments in the MFT and CDTs can affect the flow characteristics and associated factors in the system.

Numerical study of NOx emission reduction by MILD and air staged synergistic combustion in a new type of coke oven flue

In order to address the issue of high emissions in the coke industry, we require innovative solutions. This article designs a coke oven flue with an array type secondary air nozzle, achieving the synergistic occurrence of MILD combustion and air staged combustion, which can significantly reduce nitrogen oxide emissions. However, further research is needed on the optimal control methods for synergistic combustion effects. First, Analyzed the mixing state of air and fuel under different air mass flow ratios. Next, by taking into account the oxygen distribution law, analyze the temperature distribution in both the primary and secondary combustion zones. Finally, analyze the distribution of NOx concentration. Study the impact of temperature differences caused by air mass flow ratio in synergistic effects on NOx emissions. The results indicate that by adjusting the air flow ratio, the air vortex intensity in the collaborative combustion process can be enhanced. This method can reduces flame temperature, achieving the objective of reducing NOx concentration. In the new type of coke oven flue, when the air mass flow ratio is 0.4, the combustion state in the primary and secondary combustion zones is optimal, and the NOx emission concentration is 312.88 mg/m3, representing a reduction of 38 %.

Exergy efficiency and sustainability indicators of forced convection mixed mode solar dryer system for drying process

The study investigates the effectiveness of a mixed-mode solar dryer (MSD) featuring two double-pass solar air collectors in series, with a focus on dehydrating cluster figs characterized by high moisture content and rapid deterioration. Exergy analysis is a powerful tool to assess the efficiency and sustainability of drying systems. The study involves experimental data obtained from the drying process under different air mass flow rates (0.018–0.062 kg/s). The solar radiation intensity ranged from 120 W/m2 to 750 W/m2 during these experiments. The solar air collectors and mixed mode dryer exergy efficiency is found to be dependent on solar radiation intensity, showing increased efficiency with higher air mass flow rates due to enhanced heat removal and reduced losses to the surroundings. The findings reveal that the optimal air mass flow rate of 0.062 kg/s yields the highest exergy efficiency in the solar air collectors. The overall exergy efficiency of the mixed-mode solar drying chamber increases with higher air mass flow rates, ranging from 18.8 % to 41.4 %. Improvement potential (IP) analysis indicates that, as the air mass flow rate increases, the potential for reducing exergy losses decreases. The sustainability index (SI), measures the environmental impact, and it ranges from 1.26 to 1.71, with higher values associated with higher exergy efficiency.

Study on the Effects of Inflow Parameters on the Auto-Initiation of Hydrogen-Rich Gas Rotating Detonation

ABSTRACT To obtain a comprehensive understanding of the auto-initiation characteristics of rotating detonation with the high-temperature hydrogen-rich gas. The experiment was carried out with hydrogen-rich gas as fuel and ambient temperature air as oxidant. The high-temperature hydrogen-rich gas was a kind of fuel-rich gas produced by the pre-combustion of hydrogen and oxygen. The effects of inflow parameters such as air mass flow rate, hydrogen mass flow rate, and hydrogen-rich gas temperature on the auto-initiation delay time and velocity of rotating detonation waves (RDWs) were experimentally studied. The experimental results showed that when the hydrogen and air mass flow rates were 6.3 ~ 17.4 g/s and 314 ~ 610 g/s, respectively, auto-initiation could be successfully achieved and a stable RDW could be formed. As the hydrogen and air mass flow rates increased, the auto-initiation delay times decreased from 40 to 5 ms and from 45 to 19 ms, respectively. When the temperature of the hydrogen-rich gas increased from 460 to 690 K, the auto-initiation delay time decreased from 100 to 10 ms, the RDW velocity decreased from 1368.5 to 1231 m/s. Hydrogen-rich gas has a high temperature, which is easy to cause the non-detonative combustion ahead of the wave of air and hydrogen-rich gas in the RDC, which consumes part of the fuel and resulting in a decrease in the RDW velocity.

A novel solar tower simulator for hydrogen regeneration by thermo-catalytic cracking of Ammonia: Energy, Exergy, and CFD investigations

This paper presents a novel concept of a central solar tower-based hydrogen regeneration system by thermo-catalytic cracking of ammonia. This includes a closed volumetric receiver for ammonia heating and cracking, a 2.45 kWe high-concentration radiation source, and an air-cooling system for the radiation source. The thermodynamic analysis shows that the net solar-to-hydrogen generation efficiency, first law efficiency, and exergy efficiency are 31 %, 82 %, and 79.8 %, respectively, for the optical efficiency of 35 %, the conversion efficiency of 99 %, and the waste heat recovery fraction of 20 %. The simulations with an ammonia flow rate of 1 kg/hr and flux concentration of 1200 Suns show the regeneration of 1.27 kg H2/day at Jodhpur and 1.57 kg H2/day at Ladakh. Monte Carlo ray tracing simulations revealed that the developed radiation source provides an average flux of ∼ 2 MW/m2 onto a spot size of 20 mm with an efficiency of about 31 %. Reynolds-averaged Navier Stokes-based analyses are used to design a novel air-cooling system for the radiation source. The computations show that (a) an unequal distribution of air mass flow rates at the front mḟ and back mḃ, should be preferred with mḟ>mḃ, and (b) for a total mass flowrate of 0.1 kg/s with mḟmḃ = 4, the maximum surface temperature of reflectors and Xe-arc lamps is less than 315 K and 610 K, respectively. The investigations revealed the feasibility of the concept and provided valuable insight for the planned experimental assessment and scale-up of the solar tower simulator.

Thermodynamic analysis of lined rock caverns for initial inflation and cyclic operational conditions in compressed air energy storage

With the irreversible trend towards cleaner and lower carbon energy alternatives on a global scale, the Lined Rock Cavern (LRC) compressed air energy storage technology emerges as a promising solution, offering vast prospects for large scale energy storage. This study explores the thermodynamic behaviors that arise from complex factors under high-frequency charging and discharging conditions in compressed air energy storage. It comprehensively considers transient gas flow, heat transfer, and real air properties, employing Computational Fluid Dynamics (CFD) methods. The simulations and analyses focus on the temperature and pressure variations inside the cavern during the initial inflation and cyclic operational conditions, along with the heat transfer characteristics of the sealing layer steel plate, concrete lining, and surrounding rock. As revealed by the research results, the inlet temperature and the air mass flow rate are two key factors affecting the average temperature inside the cavern during the initial inflation. Specifically, the inlet temperature shows a linear relationship with the average temperature while the air mass flow rate exhibits a nonlinear relationship. By fitting the simulation results, expressions that enable effective control of the average temperature are obtained. Under cyclic operational conditions, the pressure inside the cavern fluctuates within the range of 6 MPa to 10 MPa, displaying regular oscillations. With an increase in the number of cycles, the average temperature inside the cavern exhibits a decreasing trend, eventually stabilizing within a fixed range of fluctuations, indicating that the cavern has reached a steady state. The temperature of the steel plate and concrete lining undergoes significant changes throughout the entire operational cycle, influenced by both convective heat transfer and thermal conduction. With an increase in the number of cycles, their temperature variations align with the changes in the average temperature inside the cavern. In contrast, the temperature of the surrounding rock fluctuates within a narrow range throughout the process. The research findings of this study enable a more accurate estimation of the temperature variation range inside the cavern, facilitating the optimization of cavern design and providing crucial guidance for the application of lined rock caverns compressed air energy storage systems.

Research on operation characteristics of wind supercharged solar chimney dust haze removal street light

To realize distributed dust haze removal in street canyons, an innovative wind supercharged solar chimney dust haze removal street light is proposed. The design couples solar chimney technology with municipal street lighting, utilizing thermal pressure, chimney effect and wind supercharged wheel to power the system, which achieves the dual function of lighting and dust haze removal. Operational testing on a small-scale model showed: the airflow warms up the most in the inlet area, and the model creates updrafts with a dust haze removal effect. The filtration system consists of various filter screens arranged by descending filtration efficiency: HEPA, primary filter cotton, activated carbon and nylon filter screens, with airflow velocity in the flow runner in the opposite order. The average filtration efficiency is positively correlated with the pressure drop and negatively correlated with the overflow airflow. A combination of different material filter screens is more effective than simply increasing the thickness of a single filter screen. A single layer of 10 mm primary filter cotton has the highest total mass flow of clean air, reaching 4.18 g. HEPA has the highest average filtration efficiency at 93.1 %. This innovative approach offers an efficient solution for urban air purification while maintaining street lighting functionality.

Thermo-Economic Analysis of Thermoelectric-Based Atmospheric Water Harvesters: Flow Configuration Impacts

In recent years, thermoelectric cooling has seen significant growth, driven by advancements in nanoscience and manufacturing. Concurrently, the increasing water crisis in various regions has led to a surge in research on Atmospheric Water Harvesters (AWHs) for decentralized water harvesting. This study presents a comprehensive thermodynamic and economic analysis of Thermoelectric-based Atmospheric Water Harvesters (TAWHs) with different Heat Exchanger (HX) configurations with different flow configurations. Our research identifies five types of HXs, each characterized by its own optimal geometrical and controlling parameters. These HXs are evaluated based on economy, eco-friendliness, productivity, air cooling efficiency, and compactness. We provide new insights into the hidden potential and performance of Thermoelectric Coolers (TECs) in desalination, particularly highlighting the effect of increasing the ratio of surfaces mounted with TECs to the total surface area of the channels. Our results indicate that among the HX configurations, the counter flow HX is the most economical option, capable of water harvesting at a cost of $0.230 USD per liter from an 80% humidity level. The parallel flow HX demonstrates higher efficiency according to the second law of thermodynamics and environmental friendliness, while the crossflow HX exhibits lower overall efficiency. We found that the optimum cold channel incoming air flow rate varies with humidity in a detailed analysis of a counter flow HX with 2 columns and 15 rows. Interestingly, we found that humidity and incoming air mass flow rate have a negligible effect on power consumption. This work can be used as a guideline for future engineering problems involving the design and optimization of TAWHs.

Enhancement of Air-Blower Performance by Modified Blades Configuration using Computational Fluid Dynamics (CFD)

Air blowers are critical components in various industrial applications, including HVAC, pneumatics, and the aeration process, where efficient air movement is essential. This study focusses on evaluating the aerodynamic performance, including pressure distribution, velocity profiles, and flow patterns within the blower using atransient solver method. Three different turbine designs are modelled and investigated for their performance analysis. Spline and elevated spline turbines are proposed for this study's performance improvement, and these designs are compared to the narrow turbine designs. The results from ANSYS CFD provided detailed insights into the internal flow dynamics, enabling the identification of key parameters that influence the blower’s performance, such as blade geometry and housing design. Through this analysis, valuable recommendations are offered for optimising air-blower designs to enhance their operational efficiency and reliability. The study reveals that the spline turbine design has a higher air mass flow rate compared to other designs. By utilising various impeller and housing geometries, further research is anticipated to aid in the creation of air blower designs that are more energy-efficient, which will have an impact on lower operating costs and increased sustainability in industrial operations. Our long-term objective is to reduce energy usage and maximise air blower performance. In the end, this will result in an economical and ecologically beneficial solution for a range of industrial applications.

Modeling and Control of Multi‐Stack Fuel Cell Air System based on Nonlinear Model Predictive Control Method

Hydrogen is crucial for achieving SDGs by driving energy transition and combating climate change. Proton exchange membrane fuel cell technology, leveraging hydrogen, faces challenges in meeting high‐power demands. The multistack fuel cell system (MFCS) tackles this by integrating multiple substacks, yet its air supply needs meticulous control. Proportional integral derivative (PID) decoupling from single‐stack falls short of MFCS. This article proposes nonlinear model predictive control (NMPC) for optimized air flow and pressure decoupling. Modeling MFCS's air system and designing a predictive model, it is aimed to ensuring precise control of air flow and pressure in each substack. The decoupling experiments show that NMPC outperforms PID, accurately managing air flow and pressure and reducing load fluctuations. For air mass flow, NMPC cuts mean‐absolute error (MAE) by 64.56% and root‐mean‐square error (RMSE) by 81.36%. For pressure, MAE drops 81.23% and RMSE 83.59%. Comprehensive step load tests confirm NMPC's precise, dynamic regulation too, compared to PID, NMPC lowers average MAE for air mass by 20.67%, pressure by 32.22%. RMSE improvements of 31.08% and 33.23% highlight NMPC's strength. NMPC's quick response mitigates coupling issues, enhancing vehicle load adaptability.

Evaluating long-term operational data of a Very Large Crude Carrier: Assessing the diesel engines waste heat potential for integrating ORC systems

Given the spotlight on waste heat recovery (WHR) technologies for decarbonizing the shipping industry, critically assessing waste heat from propulsion and auxiliary engines using actual data is crucial for accurately predicting fuel and carbon savings. This paper addresses this by applying advanced data processing, considering voyage characteristics, and developing methods for mapping waste heat from main engine (ME) and diesel gensets (DGs) operations using long-term operational data from a Very Large Crude Carrier (VLCC) case study. Two methods predict unrecorded air mass flows by implementing heat balance: one using measured temperature values and the other estimating exhaust gas mass flow rates based on fuel oil consumption. Within the main objectives of this study is to examine the impacts of employing the exhaust gases of both ME and DGs to evaporate recuperative ORC working fluid on power output and vessel annual carbon savings, with the formed diesel engines operational profiles serving as inputs. Simulations show a power output of 530 kW using ME exhaust gases, increasing to 653 kW and 741 kW with DGs integration for R245fa and R1233zd(E) as the selected ORC working fluids, respectively. The proposed solutions can reduce annual CO2 emissions by 4 % to 7 %.

CFD modeling of a modern wood stove - Soot formation

Wood stoves are important domestic heating appliances using renewable bioenergy. However, the emission of Particulate Matter (PM) is the major concern for the application of wood stoves. Thus, improvements in the design of wood stoves are required for the reduction of PM emissions (mainly soot) to fulfill the increasingly stringent pollutant emission limits. To achieve low PM emission of the wood stove, a 3D steady-state CFD model is used to simulate the wood stove with a focus on soot formation in this study. The model is evaluated with the experimental data, the results of which show that the CFD model provides a reasonable prediction of wood stove experiments, indicating that the CFD model can be used as an efficient tool to optimize the design of the wood stove. The model is further used to study the effects of injection direction and mass flow rate of the tertiary air on the soot particle emission. It is found that the horizontal- and down-direction injectors can effectively reduce soot formation and an optimized tertiary air mass flow rate exists in the modern wood stove system. These conclusions are very useful in designing and developing the intelligent control system of the modern wood stove.

Investigation of the utilization of forest woodchips in a commercial small-scale open-top gasifier

The present work investigates the gasification of forest woodchips, which also contain needles, branches and cones, in an 85-kW open-top gasifier with 60 %–100 % load. This lower quality fuel has higher contents of ash, bark and fines compared to typical requirements of commercial small-scale gasifiers. The woodchips were utilized in unsieved and sieved (>10 mm) fraction. By using gas analysis and temperature measurements at a high local and temporal resolution, three main novel results were found: 1) The results of this work confirm that preferential paths in the fuel bed, caused by the fines content, led to a worse gas quality. The positive effects of a load reduction (i.e., increasing hydrogen and decreasing tars contents) were not found with the unsieved fuel. 2) Opposite trends for the methane concentration with the load were found with unsieved and sieved fuel. The preferential paths probably prevented the complete decomposition of longer-chain hydrocarbons and increased the intermediate product methane, while the non-methane hydrocarbon content reduced at a similar rate with both fuel fractions. 3) When using unsieved fuel, reducing the load massively decreased the fluctuations of the air mass flow and the total hydrocarbon content. With sieved fuel, however, a satisfying process stability was already achieved in all loads. Therefore, an appropriate load management was identified to enable the utilization of fuels with higher fines contents. With these new findings, forest chips in unsieved and sieved form can be successfully used in small-scale open-top gasification.

Determination Of Two-Phase Flow Regimes Of A Condensing Water-Air Mixture In An Array Of Micro Channels

Proton exchange membrane (PEM) full cells (FCs) are a promising alternative to combustion engines for mobile applications. Their signature low operating temperature leads to the possible existence of product water in its liquid form. Liquid water formation and transport are important phenomena to understand and model in order to facilitate the development of new, more efficient PEMFCs. This contribution investigates the two-phase flow phenomena separately by introducing a gaseous air-vapor mixture into an optically accessible fuel cell flow plate with 14 parallel micro channels (confinement number Co = 7.3) and a carbon paper inlay representing the FC's gas diffusion layer and bringing it to the point of onset of condensation. Special care is taken to provide a controlled and reproducible air-vapor mixture with low pressure pulsation. One key feature of the experiment is that the flow plate used is designed to be as similar to a regular research fuel cell flow plate as possible, retaining its channel surface properties and electrical parameters. It can also be heated to a given temperature to mimic the fuel cell operating conditions. Therefore, the same plate can also be used in in-situ experiments in an operated fuel cell. An air mass flow rate of 500 - 1000 mLn / min with relative humidities of 75% - 95% at 65°C and 75°C was investigated. The emerging flow patterns were captured using a high-speed camera at 250 Hz and categorized using canonical two-phase flow regime nomenclature. It is shown that the present setup can produce the relevant two-phase flow patterns that can be found in operated fuel cells as reported by previous studies and is furthermore equipped to investigate flow states not easily reached with an operated fuel cell (e.g. flooded channels).

Effect of channel depth ratio and absorber plate configuration on performance of a solar air heater

An experimental evaluation of the effect of channel depth ratio and absorber plate configuration on the performance of a baffled counter flow double-pass solar air heater (BCDSAH) is main objective of current work. The BCDSAH was constructed so as to permit adjustments of channel depth ratio (CDR) to 2, 3 and 4. During experimentation, the lower channel depth was kept at 50 mm while the upper channel depth was adjusted to 100 mm, 150 mm and 200 mm, yielding various channel depth ratios. The assessments were conducted for three configurations of absorber plate: (i) flat absorber plate, (ii) baffled absorber plate and (iii) baffled absorber plate with phase change material (PCM). The performance of the BCDSAH was evaluated at an air mass flow rate of 0.07 kg/s for temperature rise, useful heat gain (UHG), energy efficiency, and exergy efficiency. For CDR = 2 and a baffled absorber plate with PCM, the obtained average values of temperature rise, UHG, energy efficiency and exergy efficiency were 15.3 °C, 1075.2 W, 76.2 % and 2.7 % respectively. For the baffled absorber plate with PCM, increases of 8.5 %, 9.4 %, 10.1 % and 10.9 % were obtained in temperature rise, UHG, energy efficiency and exergy efficiency respectively for CDR = 2 compared to CDR = 4. Finally, a value of CDR = 2 and a baffled absorber plate with PCM are suitable for applications like drying of agricultural products and space heating.

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime.