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Hydrogen is a novel medical gas with several properties, including anti-oxidative, anti-inflammatory, anti-apoptotic, anti-allergic, and energy metabolism stimulating properties. Hydrogen therapy has been proven effective in the treatment of myocardial ischemia, myocardial infarction, and ischemia-reperfusion injury. Diabetic cardiomyopathy (DCM) is a serious cardiovascular complication of long-term chronic diabetes that is linked to increased heart failure and arrhythmia morbidity. The effect of hydrogen on the pathogenesis of DCM is yet to be determined. Metformin is a well-known pharmacological agent for the treatment of diabetes; however, the application of large doses of the drug is limited by its side effects. Therefore, this highlights the importance of developing novel therapies against DCM. In this regard, we investigated the effect of hydrogen on DCM and the mechanisms that underlie it. Furthermore, we also assessed the efficacy of co-administration of metformin and hydrogen. In this study, we found that hydrogen improved cardiac dysfunction and abnormal morphological structure in streptozotocin-induced diabetic mice. As a mechanism, it was confirmed that hydrogen mediated its action by reducing pyroptosis via inhibition of the AMPK/mTOR/NLRP3 signaling pathway and ameliorating fibrosis via inhibition of the TGF-β1/Smad signaling pathway. Furthermore, our findings suggested that co-administration of hydrogen and metformin shows potent protective effects, as evidenced by increased survival rates, reduced fasting blood glucose, and decreased cell injury when compared to a single application of metformin. In conclusion, our study demonstrated that hydrogen inhalation attenuates DCM by reducing pyroptosis and fibrosis and that hydrogen can be combined with metformin to exhibit a more potent cardioprotective effect in DCM.

The energy used by the heart is generated mainly by the metabolism of fatty acids and glucose. Trimetazidine (TMZ) inhibits fatty acid metabolism and is used for the treatment of heart diseases such as heart failure. 3-Bromopyruvate (3-BrPA) can suppress glucose metabolism, and it is considered a promising candidate agent for tumor therapy. Because TMZ and 3-BrPA can separately inhibit the 2 main cardiac energy sources, it is necessary to investigate the effects of 3-BrPA combined with TMZ on the heart. Forty male Wistar rats were randomly divided into 4 groups: a control group, a TMZ group, a 3-BrPA group, and a 3-BrPA + TMZ group. Weight was recorded every day, and echocardiography was performed 14 days later. Heart function, the levels of adenosine triphosphate, oxidative stress-related factors (ROS, glutathione, oxidized glutathione, malondialdehyde, superoxide dismutase and total antioxidant capacity), and apoptosis in heart tissues were assessed to evaluate the effects of 3-BrPA and TMZ on the heart. In our study, no obvious changes occurred in the 3-BrPA group or the TMZ group compared with the control group. The combination of 3-BrPA and TMZ worsened heart function, decreased adenosine triphosphate levels, and increased oxidative stress and myocardial apoptosis. In conclusion, 3-BrPA and TMZ are not recommended for concurrent use.

It is noteworthy that prolonged cardiac structural changes and excessive fibrosis caused by myocardial infarction (MI) seriously interfere with the treatment of heart failure in clinical practice. Currently, there are no effective and practical means of either prevention or treatment. Thus, novel therapeutic approaches are critical for the long‐term quality of life of individuals with myocardial ischaemia. Herein, we aimed to explore the protective effect of H2, a novel gas signal molecule with anti‐oxidative stress and anti‐inflammatory effects, on cardiac remodelling and fibrosis in MI rats, and to explore its possible mechanism. First, we successfully established MI model rats, which were then exposed to H2 inhalation with 2% concentration for 28 days (3 hours/day). The results showed that hydrogen gas can significantly improve cardiac function and reduce the area of cardiac fibrosis. In vitro experiments further proved that H2 can reduce the hypoxia‐induced damage to cardiomyocytes and alleviate angiotensin II‐induced migration and activation of cardiac fibroblasts. In conclusion, herein, we illustrated for the first time that inhalation of H2 ameliorates myocardial infarction‐induced cardiac remodelling and fibrosis in MI rats and exert its protective effect mainly through inhibiting NLRP3‐mediated pyroptosis.

As a reliable stall warning strategy, the fast wavelet method was introduced to successfully predict the aerodynamic instability of a multistage axial flow compressor. One single sensor installed at each stage is proved to be sufficient to predict the stability status in a three-stage axial flow compressor. The whole prediction strategy includes the dynamic pressure signal capture, disturbance extraction using decomposition and reconstruction via fast wavelet transform, and stall warning index calculation based on statistical probability distribution. On this premise, the first occurrence of the stall in this three-stage axial flow compressor is predicted to be within the first stage, which is consistent with the stall route captured by the eight transducers around the casing wall. Thereafter, the stall warning index is used to monitor the stability status during the continuous throttling process. Furthermore, the validation using tip air injection and inlet radial distortion indicated that the stall warning index decreases as the compressor's stability improves. Conversely, the deterioration of stability causes the increase of the stall warning index. Thus, experimental results demonstrate that the stall warning method based on fast wavelet analysis can predict the aerodynamic instability in actual application.

The present paper provides a summary of investigations of the tip air injection, which has been studied for over 30 years to extend the stall margin in axial flow compressors. The review covers the design of injected parameters, understanding of stability-enhancing mechanism, application of active control, and self-recirculation based on tip air injection. First, the injected parameters that can influence the stability-enhancing capability are surveyed and classified. These include injected mass flow and momentum, structure, pitch and yaw angle, axial location, and circumferential distribution. Next, the effect of tip air injection on the internal flow field is introduced; the action on the main stream flow or tip leakage flow depends on the injected moment ratio. Finally, the applications of active control with tip air injection and self-recirculating injection from a single-rotor to multi-stage compressors are listed and discussed. The active control methods are based on the Moore–Greitzer model and online prediction of stall inception. This study aims to aid researchers who are working on stability enhancement with tip air injection in compressors to improve their work. Moreover, considering that the regulation of injected mass flows or momentums is flexible, this study would facilitate the immediate application of the tip air injection in actual aero-engine compressors.

The unsteady tip leakage flow (UTLF) is experimentally studied to observe the circumferential propagation in axial flow compressors. The evolutionary process of the circumferential propagation is captured by utilizing a collection of time-resolved pressure transducers on the casing with circumferential and chord-wise spatial resolution. Results show that the circumferential propagation dominated by the UTLF exists and occurs only after the emergence of the UTLF in the throttling process. Since then, the propagating speed and the scale of disturbance gradually augment, until the transition to the propagating speed and scale of stall inception. The tip air injection is applied to further verify the aforementioned circumferential propagation. Two kinds of injected momentum ratios, namely, micro and macro injection adopted in single-rotor compressor, and two types of injected methods, i.e., external air source and self-recirculation applied in single-stage and three-stage compressor demonstrate that either micro injection with a small stall margin improvement (SMI) or macro injection with a large SMI, or the different injected types in single- and three-stage compressor, with the increasing stability-enhancing capability of tip air injection, the UTLF is effectively weakened, and the circumferentially propagating speed and the scale of the disturbance dominated by UTLF accordingly shows a decreasing trend. The above results provide guidance for understanding the relationship between the UTLF and stall inception in terms of circumferential propagation that can be used to predict the compressor stability.

To survive in a complex environment, nature has produced efficient and versatile resource-rich structures. One of the novel drag reduction designs comes from the efficient movement of sharks through microscope riblets aligned along the flow direction. In this paper, the effectiveness of sharkskin-inspired riblets in reducing the aerodynamic loss of compressor cascade flow was investigated using the high-fidelity numerical simulation method. Two key normalized parameters, i.e., s+ and h+, were selected to parameterize various riblet designs, and the corresponding relative change in cascade performance was first investigated based on the unsteady Reynolds-averaged Navier–Stokes (uRANS) simulations with/without a transition model. Then, the large eddy simulations in conjunction with the wall-adapted local eddy viscosity model were conducted to investigate the cascade flow with the selected riblet design cases. By comparing the flow resistance, transition positions, vortex formations, and turbulence fluctuations of the boundary flow, the flow control mechanisms of the riblets were finally studied. Simulation results show that compared with the prototype case, the total pressure loss can be reduced by up to 20.5% in the fully turbulent environment. This is because the spanwise fluctuation of the turbulent vortices is impeded inside the boundary layer, and the turbulent vortices are lifted above the riblet tip. Low-speed streaks inside the riblet valleys generate relatively low shear stresses, while the high-shear stresses occur only at the riblet tips. However, when considering the transition from laminar to turbulent boundary flow, the aerodynamic performance of compressor cascade strongly depends on the riblet position relative to the transition region on cascade suction side (SS). The total pressure loss can only be reduced by up to 8.1%, and even most riblet designs degrade the cascade performance. The major reason is that the riblets are located upstream of the transition zone, especially at the small incidence angles. Due to the installation of riblets, the contact area between the laminar flow and the wall surface is increased, and the downstream laminar-to-turbulent transition is promoted.

With the large-scale application of machine learning in various fields, the security of models has attracted great attention. Recent studies have shown that tree-based models are vulnerable to adversarial examples. This problem may cause serious security risks. It is important to verify the safety of models. In this paper, we study the robustness verification problem of Random Forests (RF) which is a fundamental machine learning technique. We reduce the verification problem of an RF model into a constraint solving problem solved by modern SMT solvers. Then we present a novel method based on the minimal unsatisfiable core to explain the robustness over a sample. Furthermore, we propose an algorithm for measuring Local Robustness Feature Importance (LRFI). The LRFI builds a link between the features and the robustness. It can identify which features are more important for providing robustness of the model. We have implemented these methods into a tool named VARF. We evaluate VARF on two public datasets, demonstrating its scalability and ability to verify large models.

The reliability of widely studied four stall warning methods, namely, auto- and cross-correlation, Root-Mean-Square (RMS), and fast wavelet analysis, were experimentally studied in a low-speed axial flow compressor. Unsteady pressures used for stall warning were measured by time-resolved sensors mounted on the casing along axial and circumferential spatial resolution. Three influence factors of rotational speed fluctuation, circumferential and axial location of pressure sensors for the stall warning reliability were analyzed and discussed. The rotational speed fluctuation that inevitably exists in the actual aero-engine would lead to the phase shift of phase-locked pressure data and thus deteriorates the stall warning reliability using the auto-correlation and RMS analysis methods. The circumferential location of pressure sensors would affect the reliability of proposed stall warning methods due to the uneven tip clearance distribution. Auto-correlation, RMS, and fast wavelet methods are more effective at the large tip clearance location than at the small tip clearance location. For the cross-correlation method that needs two symmetrically-arranged pressure sensors, the negative effect caused by the circumferential unevenness of tip clearance size can be avoided. The ideal axial location of the sensor installation for stall warning is near the rotor leading edge where the strong tip leakage flow fluctuation exists. In addition, considering the actual complex inflow condition, the stall warning methods' reliability with inlet circumferential distortion was studied. In the distorted region, the adverse effect of distortion on stability can be detected by above four methods. In the undistorted region, only cross-correlation coefficient correspondingly decreased to reveal the stability margin deterioration caused by circumferential distortion. Considering the random circumferential position of distortion, cross-correlation method was proved to have a promising application compared to others.

Tip air injection for stall margin extension is experimentally investigated in a multi-stage axial flow compressor. By comparing the stall margin improvement (SMI) under tip air injection in different stages, injected air only upstream from the first stage can causes a 20% SMI. This is because stall inception appears in the first stage. From the trend curve of SMI versus injected momentum ratios applied in the first stage, two demarcation points are found that separate the curve into micro, macro, and overlarge injections. Micro injection with a small SMI only weakens the tip leakage flow. Macro and overlarge injections influence both the tip leakage flow and mainstream flow, which contribute to a large SMI. However, overlarge injection causes the second stage to stall first, and causes the SMI to remain constant with further increases in the injected momentum ratio. The outlet axial velocity and flow angle measured using a five-hole probe indicate that with the overlarge injection in the first stage, the separation of the rotor blade passage in the second stage is more adverse than those in the other stages. The adverse passage separation originating from the hub region results in the second stage losing its working capability and stalling first. Moreover, at this point, the blade tip injection in the second stage has no additional effect on the extension of the stall margin.

Aims Reperfusion therapy is the most common and effective treatment against ischemic heart disease (IHD), but the process inflicts massive ischemia/reperfusion (I/R) injury for which no treatment exists. Notably, reperfusion after ischemia causes ischemia/reperfusion injury (IR injury) and the “no-reflow” phenomenon seriously affecting the therapeutic effects in clinical practice. The principle purpose of this study is to validate the effect of hydrogen gas on IHD and further explore the mechanism of hydrogen gas in alleviating myocardial I/R injury and no-reflow phenomenon. Materials and methods The rat model of myocardial ischemia-reperfusion was well established. Myocardial infarct size was evaluated by TTC & Evans blue staining. The no-reflow area and the cardiac function were assessed by thioflavin-S staining and echocardiography respectively. Microstructure and mitochondria of myocardial tissue were assessed by transmission electron microscope. Western blot and immunohistochemistry were used to evaluate the expression of NLRP3 mediated pyroptosis related proteins. The 8-OHdG, MDA and serum total ROS were used to evaluate the degree of oxidative stress. Key findings The myocardial infarct size, no-reflow area, cardiac function, microstructure and mitochondrial morphology of I/R model rats were significantly improved after hydrogen inhalation. In addition, the expression of 8-OHdG, MDA, ROS and NLRP3 mediated pyroptosis related proteins were significantly decreased. Significance We found that oxidative stress and NLRP3 mediated pyroptosis are the important mechanisms for hydrogen to alleviate myocardial I/R injury, and we also confirmed that hydrogen can significantly improve no reflow phenomenon caused by ischemia-reperfusion.

In this paper, a novel axial slot casing treatment design is introduced via optimization to improve the stall margin of the compressor with minimal efficiency loss. Besides the conventional design parameters including the height, length, position, inclination angle and open area ratio of the slots, a series of new parameters are put forward to increase the freedom of the slot meridional profile. An in-house design optimization platform is constructed based on NSGA-II and Kriging surrogate model to perform the optimization. A Pareto Front is obtained through optimization, from which the optimal design is selected by comprehensively considering both stability and efficiency performances of the compressor, i.e. the stall margin is improved by 11.23% in conjunction with the peak efficiency reduced by 0.21%. The database is analyzed to investigate how different parameters affect the performance of the slots. Three non-dominated representative designs are selected from the Pareto Front and their influencing mechanisms on stability and efficiency are further studied. Results show that the application of slots would generate a circulated flow, which exerts suction and reinjection effects at the rotor tip region and alleviate the blockage in the blade passages. Entropy analysis indicates that the viscous shearing interaction between the reinjection flow and incoming main flow causes additional entropy generation, thus slightly reducing the peak efficiency of the compressor.

This paper describes a recently developed pressure-measuring technique based on direct current glow discharge plasma. The operation principle, characteristics and design of this plasma pressure sensor are introduced and investigated. The development of the plasma pressure sensor was motivated by the need to document the high-frequency internal information more clearly in the harsh environment of turbomachines or hypersonic flows. The electrode spacing and current were two main factors that influenced the sensor's monotonic response characteristic and static sensitivity to the pressure fluctuation. Three typical electrode spacings—50 μm, 100 μm and 220 μm—were tested for the static calibration. The results revealed that the optimal electrode spacing was 220 μm, which showed a monotonically increasing trend and had the highest sensitivity for a pressure range from 0.5 atm to 5.0 atm. The dynamic response of the sensor was calibrated with a sinusoidal-wave pressure generator and a shock tube as the step-function pressure generator. The results showed that the natural frequency of the plasma pressure sensor, including its high-voltage power supply and electronic circuit, was 146.6 kHz.

Inlet radial distortion caused by boundary layer separation is experimentally studied in a three-stage axial flow compressor. Two lattice rings were designed to generate tip and hub radial distortion, respectively, and distortion intensity was measured using a five-hole probe installed upstream of the first rotor blade row. The unsteady flow field is captured by using a collection of pressure transducers installed on the casing wall with circumferential and chordwise spatial resolution. The stall route measured on the casing wall indicates that the first stage stalls under all inflow conditions, tip radial distortion can modify the scale of stall inception to long-length scale (6–8 blade passages), unlike the uniform inflow and hub radial distortion with typical short-length-scaled inception (3–4 blade passages). Detailed measurements indicate that tip radial distortion can strengthen the tip leakage vortex and increase the tip separation to induce the compressor to stall earlier than uniform inflow. However, hub radial distortion redistributes the mainstream flow toward the blade tip region, thereby weakening the unsteadiness of tip leakage flow, reducing the outlet flow angle and increasing the outlet axial velocity near the blade tip to remove the separation or blockage, and finally extending the stall margin. The aerodynamic measurements downstream different rotor blade rows also indicate that the inlet radial distortion mainly affects the flow field at the first stage, which is obviously weakened at the second stage and completely unaffected at the third stage.

The effects of water ingestion on the performance of an axial flow compressor are experimentally studied with and without endwall treatment. The background to the work is derived from the assessment of airworthiness for an aero-engine. The stability-enhancing effects with endwall treatments under rain ingestion are not previously known. Moreover, all the endwall treatments are designed under dry air conditions in the compressor. Water ingestion at 3% and 5% relative to the design mass flow proposed in the airworthiness standard are applied to initially investigate the effects on the performance under smooth casing (SC). Results show that the water ingestions are mainly located near the casing wall after they move through the rotor blade row. The pressure rise coefficient increases, efficiency declines, and torque increases under the proposed water ingestion. The increase of the inlet water increases the thickness of the water film downstream the rotor blade row and aggravates the adverse effects on the performances. Subsequently, three endwall treatments, namely circumferential grooves, axial slots, and hybrid slots–grooves, are tested with and without water ingestion. Compared with no water ingestion, the circumferential grooves basically have no resistance to the water ingestion. The axial slots best prevent the drop of the pressure rise coefficient induced by water ingestion, and hybrid slots–grooves are the second-best place owing to the contribution of the front axial slots. Therefore, the hybrid slots–grooves can not only extend the stall margin with less efficiency penalty compared with axial slots, but also prevent rain ingestion from worsening the compressor performance.

Very high flow coefficient centrifugal compressor stages are mostly applied as the first stages of multistage compressors. The performance of this type of stages is critical to the entire centrifugal compressors, but surprisingly little related information is available in the open literature. A centrifugal compressor with high inlet flow coefficient of 0.2, presenting a narrow operating range and unstable running situation even at design speed during the test, is investigated here. To reveal flow details in this centrifugal compressor, numerical simulations have been carried out and indicate that excessive impeller flow diffusion results in the poor performance of this centrifugal compressor. With the same inlet flow coefficient, six redesign cases coming from an in-house one-dimensional analysis program are proposed together with impeller trimming and equal flow area design method for corresponding vaneless diffuser. Performance comparison among these redesign centrifugal compressors is presented and the most suitable one is recommended for test in the future. In addition, three redesign cases with lower inlet flow coefficient developed by means of flow trimming are shown in the end to satisfy potential application areas. Finally, the results in this study can provide valuable reference information for multistage centrifugal compressor design.

This research investigates the use of single dielectric barrier discharge (SDBD) actuators for energizing the tip leakage flow to suppress rotating stall inception and extend the stable operating range of a low speed axial compressor with a single rotor. The jet induced by the plasma actuator adds momentum to the flow in the tip region and has a significant impact on the tip-gap flow. Experiments are carried out on a low speed axial compressor with a single rotor. The static pressure is measured at both the rotor inlet and outlet. The flow coefficient and pressure rise coefficient are calculated. Then the characteristic line is acquired to show the overall performance of the compressor. With unsteady plasma actuation of 18kV and 60W the compressor stability range improvement is realized at rotor speed of 1500 r/min — 2400 r/min.

Numerical investigation on the self-induced unsteadiness of tip leakage flow (TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes (URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement (SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure (RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency (BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.

According to the requirements of a solar dish-Brayton system, a centrifugal compressor stage with a minimum total pressure ratio of 5, an adiabatic efficiency above 75% and a surge margin more than 12% needs to be designed. A single stage, which consists of impeller, radial vaned diffuser, 90° crossover and two rows of axial stators, was chosen to satisfy this system. To achieve the stage performance, an impeller with a 6:1 total pressure ratio and an adiabatic efficiency of 90% was designed and its preliminary geometry came from an in-house one-dimensional program. Radial vaned diffuser was applied downstream of the impeller. Two rows of axial stators after 90° crossover were added to guide the flow into axial direction. Since jet-wake flow, shockwave and boundary layer separation coexisted in the impeller-diffuser region, optimization on the radius ratio of radial diffuser vane inlet to impeller exit, diffuser vane inlet blade angle and number of diffuser vanes was carried out at design point. Finally, an optimized centrifugal compressor stage fulfilled the high expectations and presented proper performance. Numerical simulation showed that at design point the stage adiabatic efficiency was 79.93% and the total pressure ratio was 5.6. The surge margin was 15%. The performance map including 80%, 90% and 100% design speed was also presented.

This paper describes the effects of non-equilibrium air plasma generated by a dielectric barrier discharge (DBD) on the combustion of low heating value fuels. The experimental results indicate that addition of a very small amount of energy to the air flow in the form of DBD significantly improves the flame stability. Moreover, main combustion characteristics such as flame propagation speed, combustion intensity and lean blow-off limits are also enhanced by the effect of plasma. Some active radicals such as excited O atom and excited N2 molecule are observed by spectrograph in the discharge area. Based on the results of numerical investigation we can conclude that these active radicals generated in discharge area can accelerate the production rate of active OH radical which plays a key role in the oxidation process of low heating value fuel, and thus the whole combustion process is accelerated.

The DLE (dry low emission) technology has already been used on industrial gas turbine combustor and the NO X emission can be limited to 25 ppmv (@15% O 2 ), but one of the destructive effects is combustion instability. In this paper, the dynamic and emission characteristics of a DLE gas turbine combustor have been researched in the authors’ laboratory, and the results show that the key source of combustion instability is the non-uniformity of fuel in the flame zone. Two main fuel supply methods have been used to form different fuel distribution types; it is shown that in the perfectly premixed case the emission level is low and combustion process is stable. The PPF also has an obvious effect on the combustor’s emission and dynamic characteristics.

A numerical study is conducted to investigate the influence of inlet flow condition on tip leakage flow (TLF) and stall margin in a transonic axial rotor. A commercial software package FLUENT, is used in the simulation. The rotor investigated in this paper is ND_TAC rotor, which is the rotor of one-stage transonic compressor in the University of Notre Dame. Three varied inlet flow conditions are simulated. The inlet boundary condition with hub distortion provides higher axial velocity for the incoming flow near tip region than that for the clean inflow, while the incoming main flow possesses lower axial velocity near the tip region at tip distortion inlet boundary condition. Among the total pressure ratio curves for the three inlet flow conditions, it is found that the hub distorted inlet boundary condition improves the stall margin, while the tip distorted inlet boundary condition deteriorates compressor stability. The axial location of interface between tip leakage flow (TLF) and incoming main flow (MF) in the tip gap and the axial momentum ratio of TLF to MF are further examined. It is demonstrated that the axial momentum balance is the mechanism for interface movement. The hub distorted inflow could decrease the axial momentum ratio, suppress the movement of the interface between TLF and MF towards blade leading edge plane and thus enhance compressor stability.

The inlet attack angle of rotor blade reasonably can be adjusted with the change of the stagger angle of inlet guide vane (IGV); so the efficiency of each condition will be affected. For the purpose to improve the efficiency, the DSP (Digital Signal Processor) controller is designed to adjust the stagger angle of IGV automatically in order to optimize the efficiency at any operating condition. The A/D signal collection includes inlet static pressure, outlet static pressure, outlet total pressure, rotor speed and torque signal, the efficiency can be calculated in the DSP, and the angle signal for the stepping motor which control the IGV will be sent out from the D/A. Experimental investigations are performed in a three-stage, low-speed axial compressor with variable inlet guide vanes. It is demonstrated that the DSP designed can well adjust the stagger angle of IGV online, the efficiency under different conditions can be optimized. This establishment of DSP online adjustment scheme may provide a practical solution for improving performance of multi-stage axial flow compressor when its operating condition is varied.

Based on the simplified format of the Reynolds stress equations, a fire-new rotational-modification method for the anisotropic turbulence model has been presented. A three-dimensional Navier-Stokes code with this new rotational modified k-ω turbulence models (β=0.1 and β=1) and the standard k-ω turbulence model have been used for the prediction of flow and heat transfer characteristics in a rotating smooth square channel. The Reynolds number Re based on the inlet velocity of the cooling air and hydraulic diameter is 6000. The rotating speed are 300, 600, 900, 1200rpm respectively. The calculations results of using three turbulence models have been compared with the experimental data. The research results show that (1) the rotational modification coefficient Rf13 used in the new anisotropic k-ω model would increased/decreased the predictions of heat transfer on the trailing surface/leading surface compared to the standard k-ω model. And this tendency would be increased with the increased β. (2) The simulation performance of the standard k-ω model was well on the leading surface. However, on the trailing surface it under-predicted the heat transfer at high rotating speed. (3) The calculation results of the new anisotropic k-ω model with β=0.1 proposed by the present paper agreed well with experimental data, both on the leading and trailing surfaces. Besides, compared to 1, 0.1 is a more appropriate magnitude of β at conditions in the present paper.

Previously the features of circumferential propagation of self-induced tip leakage flow unsteadiness for a low speed isolated axial compressor rotor in the authors’ laboratory were discovered and investigated via numerical simulation, which only occurs below a critical stable flow point that is close to but not yet at the stall limit. Further in this paper, the detailed investigation on evolution of tip leakage flow during the throttling process into spike rotating stall was conducted by adopting the valve-throttling model. During this process, the development of the circumferential propagation of tip leakage flow unsteadiness was especially focused on. According to the unsteady characteristics of pressure signals, the evolvement of compressor flow field can be classified into four stages. As compressor throttled, the oscillation frequency of self-induced unsteady tip leakage flow decreased gradually, and thus resulted in the decrease of its circumferential propagation speed. The circumferential propagation of self-induced tip leakage flow unsteadiness is closely related with rotating instability. When the forward spillage of tip leakage flow at the leading edge occurred, the spike type rotating stall was initiated. Its flow structures were given in the paper.

Flameless combustion is a new technology with the following advantages: 1) Ultra-low emissions of both NOX and CO; 2) fuel flexibility, from liquid fuels, natural gas to hydrogen-rich syngas; 3) lower possibility of flashback and thermoacoustic oscillations. In this paper, we focus on the dynamic characteristics of a flameless model combustor. Experimental results show that flameless combustion can lower emissions while maintaining combustion stability. However, combining a pilot flame with flameless combustion may excite thermoacoustic instability.

Experimental investigations are performed in a three-stage low-speed axial compressor with variable inlet guide vanes (IGV) and adjustable stators. The characteristics of the compressor, especially the efficiency and stall margin, are analyzed in design and off-design operation conditions by adjusting stagger angles of IGV and stators as well as changing the rotational speed. The experimental results show that the off-design performance of the multistage axial compressor is improved by restaggering of IGV and stators related to rotational speed. Considering the background of engineering applications, digital signal processing (DSP) technique is used to realize online adjustment of stagger angles according to the corresponding relations between incidence angles of rotor and rotational speed.

Three dielectric barrier discharge plasma actuators were mounted at the positions of 20%, 40% and 60% of chord length on the endwall in a compressor cascade. The downstream flow field of the cascade has been measured with a mini five-hole pressure probe with and without the plasma actuation. The measured results show that the plasma actuation most effectively reduces total pressure loss and flow blockage when the actuators are operated simultaneously. As each of the actuators is operated independently, the actuator at the position of 20% of chord length most effectively reduces flow blockage, and the actuator at the position of 60% of chord length fairly reduces total pressure loss. However, negative pressure loss reduction occurs with the plasma actuator at the position of 40% of chord length. In brief, the plasma actuation placed on the endwall in the cascade apparently influences the endwall secondary flow, and the optimal locations and strength of actuation are critical for the control of endwall secondary flow in a compressor cascade with the plasma actuators.

The stall behavior in a single-stage low-speed axial compressor under rotating inlet distortion (RID) is investigated in the first half of this paper. The tests demonstrate that the tip leakage flow (TLF) plays an important role in triggering rotating stall. The tracking of the spike-like disturbances caused by the spillage of TLV indicates that most of such spike-like disturbances will be smeared by non-distorted sector and the growth of the spike-like disturbances actually relate closely to how and how often the path of the propagating disturbances come across the path of the rotating distorted sector. In the second half of this paper, micro air injections are applied to test the effect behavior of TLF on stall inception. Contrasts to without micro air injections, the spike-like disturbances are much fewer, so the possibilities that spike-like disturbances may trigger rotating stall are fewer too. As a result, the compressor gets a lower mass flow rate at stall for both co-rotating inlet distortion and counter-rotating inlet distortion.

Short-length-scale disturbances, also called spikes, are often responsible in triggering rotating stall in axial-flow compressors. One hypothesis suggests that spikes can be the consequence of dynamic interaction among forward-spilled tip-leakage flow, the main throughflow, and the reversed flow. However, the transit process of such a dynamic interaction in the vicinity of the rotor tip clearance and, thus, the physical images of the flow structure of a spike are still unknown. In this paper, we present a numerical study with a novel scheme for a low-speed axial-How compressor by incorporating rotating inlet distortion. Because the inlet distortion will overload a portion of the blades while keeping the rest working normally, the short-length-scale disturbances can be observed without advocating the computational difficulty of simulating a fully stalled compressor. Two unsteady simulations using a commercial, three-dimensional, time-accurate, Reynolds-averaged Navier-Stokes solver are performed: one for a one-fourth rotor annulus with finer grids and the other for the entire rotor annulus with coarser grids. After the code is validated by comparing experimental results with the simulation for the entire rotor annulus, the one-fourth-annulus simulation is used to unveil the flow physics. As elucidated from the computational results, the complete birth-to-decay process of the short-length-scale disturbances is captured for the first time. The corresponding 3-D flow structure is also revealed. It is shown that the effects of dynamic How interaction at the tip extend beyond the tip region and deeply into the blade span. A horn-shaped vortex with one end at about 30% of the blade span and the other end at the casing is formed, which generates a low-pressure dip in the casing-pressure measurement. The spike, as identified from casing-pressure measurement, corresponds to a flow image in which the vortex rotates around the annulus.

The principle of combustion field detection by using laser tomography, as well as exploitation of the laser tomography apparatus and the tool for image processing is described. An experiment detecting flame fronts by laser tomography was made by employing a V-shaped premixed flame. The results show that the instantaneous geometric shape of flame wrinkles within the light sheet can be clearly resolved. The contours of the flame fronts are precisely tracked through active contour models (ACM) from the digital images of laser tomography, laying the basis for the quantitative analysis of flame wrinkling and propagation.

Effects of plasma flow control are researched on the basis of plasma exciting flow experiments and numerical simulations. Turbulent model is more effective than laminar model in plasma numerical simulation as results showed. Both plasma exciting effects of acceleration and flow separation suppression are investigated through experiments carried on the flat plate and the compressor cascades. The results demonstrate that boundary layer characteristic is modified by plasma exciting. Distributions of total pressure and velocity in the wake are improved notably for 20 m/s coming velocity and the effect of plasma can still be observed while velocity is increased to 50 m/s. For low velocity flow, plasma exciting is effective in flow separation suppression.

Steady discrete micro air injection at the tip region in front of the first compressor rotor has been proved to be an effective method to delay the inception of rotating stall in a low speed axial compressor. Considering the practical application a new type of micro injector was designed and described in this paper, which was imbedded in the casing and could be moved along the chord. In order to verify its feasibility to other cases, such as high subsonic axial compressor or centrifugal compressor, some other cases have been studied. Experimental results of the same low speed axial compressor showed that the new injector could possess many other advantages besides successfully stabilizing the compressor. Experiments performed on a high subsonic axial compressor confirmed the effectiveness of micro air injection when the relative velocity at the blade tip is high subsonic. Meanwhile in order to explore its feasibility in centrifugal compressor, a similar micro injector was designed and tested on a low speed centrifugal compressor with vaned diffuser. The injected mass flow was a bit larger than that used in axial compressors and the results showed micro injection could also delay the onset of rotating stall in the centrifugal compressor.