Strong Pulsations Research Articles

Numerical Simulation of the Unsteady Airwake of the Liaoning Carrier Based on the DDES Model Coupled with Overset Grid

The wake behind an aircraft carrier under heavy wind condition is a key concern in ship design. The Chinese Liaoning ship’s upturned bow and the island on the deck could cause serious flow separation in the landing and take-off area. The flow separation induces strong velocity gradients and intense pulsations in the flow field. In addition, the sway of the aircraft carrier caused by waves could also intensify the flow separation. The complex flow field poses a significant risk to the shipboard aircraft take-off and landing operation. Therefore, accurately predicting the wake of an aircraft carrier during wave action motion is of great interest for design optimization and recovery aircraft control. In this research, the aerodynamic around an aircraft carrier (i.e., Liaoning) was analyzed using the computational fluid dynamics technique. The validity of two turbulence models was verified through comparison with the existing data from the literature. The upturned bow take-off deck and the right-hand island were the main areas where flow separation occurred. Delayed detached eddy simulation (DDES), which combines the advantages of LES and RANS, was adopted to capture the full-scale spatial and temporal flow information. The DDES was also coupled with the overset grid to calculate the flow field characteristics under the effect of hull sway. The downwash area at 15° starboard wind became shorter when the hull was stationary, while the upwash area and turbulence intensity increased. The respective characteristics of the wake flow field in the stationary and swaying state of the ship were investigated, and the flow separation showed a clear periodic when the ship was swaying. Comprehensive analysis of the time-dependent flow characteristic of the approach line for fixed-wing naval aircraft is also presented.

Intraoperative severe gastric venous congestion during total pancreatectomy with replaced common hepatic artery: a case report

BackgroundGastric venous congestion (GVC) is one of the complications of total pancreatectomy (TP). Here, we report a case of intraoperative severe GVC during TP with a replaced common hepatic artery (RCHA).Case presentationA 65-year-old female patient was diagnosed with intraductal papillary mucinous carcinoma. Her CHA branched from the superior mesenteric artery as RCHA. She underwent subtotal stomach preserving TP. The tumor was resected with splenic artery (SpA) and total gastric vein transections. Severe GVC and bleeding from the stomach tube occurred intraoperatively. A strong pulsation was observed in the left gastric artery (LGA), and we suspected an increased blood flow from the celiac artery (CeA) to the LGA after SpA resection. Total gastrectomy (TG) was then performed to control the severe GVC-related bleeding. The patient was discharged without complications 19 days postoperatively.ConclusionTP with RCHA may increase the risk of severe GVC due to increased blood flow from CeA to LGA.

Establishing Baselines for Six Short-period δ Scuti Variables

As part of our variable star follow-up program, we have examined a number of stars from the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey. Using a combination of our own data, ATLAS data, and other archival data, we confirmed the published periods and established a baseline ephemeris for each star. This initial sample of six stars are from the PUL or mono-periodic set from the ATLAS survey. Our determined periods agreed well with the published values. Five targets were found to be high amplitude δ Scuti variables (HADS), and one a low-amplitude δ Scuti (LADS). Beyond the primary period we examined the frequency content, Q value, position in the PL relation, and position within the instability strip of each object. We found ATO J070.9950+37.4038 to be the most complex target. The frequency content is likely a set of nonradial pulsations. ATO J328.8034+58.0406 is a multiperiodic HADS variable that is pulsating in the first and second overtones. ATO 345.4240+42.0479 was found to be a simple HADS monoperiodic fundamental pulsator. In the case of ATO J086.0780+30.3287, we found a strong fundamental pulsation with many harmonics and a weaker first overtone pulsation. We classify ATO J086.0780+30.3287 as a HADS. ATO J077.6090+36.5619 was found to be an interesting case of a monoperiodic star that appears to be pulsating in the third overtone. The lower amplitude for this target would put it in the LADS group. ATO J045.8159+46.0090 was found to be a multiperiodic HADS pulsating in the first and second overtones.

Transient Flow-Induced Stress Investigation on a Prototype Reversible Pump–Turbine Runner

Pump–turbine units with high heads are subjected to strong pressure pulsations from the unsteady transient flow in fluid channels, which can produce severe vibrations and high stresses on the pump–turbine structural components. Therefore, reducing transient flow-induced stresses on prototype reversible pump–turbine units is an important measure for ensuring their safe and efficient operation. A high-head prototype reversible pump–turbine with a rated head of 440 m was used to investigate the transient flow characteristics and the flow-induced-stresses in this study. First, the flow passages of the pump–turbine unit and the structure of the reversible pump–turbine runner were constructed with CAD tools. Next, CFD simulations at the full load were performed to investigate the pressure pulsation characteristics of the pump turbine in both the time domain and the frequency domain. After this, the pressure files calculated by the CFD were exported and applied to a finite element model of the pump–turbine runner to calculate the transient flow-induced dynamic stresses. The results show that the pressure pulsations in the flow passage are closely related to the rotational speed, the guide vane number, and the runner blade number of the pump–turbine unit. The maximum flow-induced stresses on the pump–turbine runner at the full load were below 2 MPa and lower than the allowable value, which reveals that the designs of the pump–turbine runner and the flow passage are acceptable. The conclusions can be used as a reference to evaluate the design of high-head pump–turbines units. The approaches used to carry out the transient flow-induced stress calculations can be applied not only to pump–turbines units but also to other types of fluid turbomachinery such as pumps, turbines, fans, compressors, turbochargers, etc.

Analysis of the temporal, spatial, and frequency law of the internal flow in a prototype vaned mixed‐flow pump

AbstractMixed‐flow pump is a typical pump using in low‐head cases of water lifting. The flow field pulsation is usually an important issue in the operation of mixed‐flow pumps and their pumping statins. Due to its large size, it is difficult to monitor the internal flow characteristics well, based on computational fluid dynamics, we use 5678 monitoring points which arranged in the impeller and fixed vane with using the high pulsation tracking network, and the pressure pulsation signals are analyzed by fast Fourier transform and variable mode decomposition to decompose the main frequency and intensity of the pressure pulsation signals, then analyze the energy dissipation with the entropy production rate (EPR). It is found that there are strong low‐frequency (0.416, 0.625, and 1.67 Hz) pressure pulsation near hub, and the pressure pulsation on the shroud is stronger than that on the hub (at least three times or more); there are strong and stable pressure pulsation (25 Hz) on the shroud generated by the rotor–stator interference (RSI); and the EPR in the flow field can be well combined with the signal. Reasonably allocating material strength and controlling the number of vanes and impellers to avoid producing a common multiple can avoid pressure pulsation caused by RSI and reduce energy dissipation. Therefore, it is very effective in improving the efficiency of this part. Under low flow conditions, the siphon outflow passage can predict the high‐frequency (45.833 Hz) attenuation area well through the phase signal decomposition of the signal, which has certain significance for improving its stability and efficiency.

The BT-SAM-Net: a new framework of end-to-end periodic time-series fault diagnosis for aero-pipelines systems

Accurate recognition of aero-engine pipeline faults is of great significance for engine maintenance costs and downtime. Pipeline signals have a strong periodic time series correlation under strong pump source pressure pulsation stimulation. However, very few studies have considered the correlation of features at pulsation period time points. Additionally, it is challenging to realize intelligent fault diagnosis of weak characteristics of pipeline faults due to the influence of vibration-noise coupling of aero-engines. The time information feature extraction model combined with self-attention mechanism (BT-SAM-Net), a newly created fault detection framework end-to-end time-series and anti-noise, is presented for the aero-pipeline in order to close the aforementioned research gaps. The primary goal of the proposed framework is to accomplish intelligent classification tasks by using the measured aero-pipeline raw data as the model input. Firstly, a two-way time series information fusion model is creatively designed, which is the first attempt to analyze the difference in time series correlation characteristics of faults for aero-pipelines. Secondly, The BT-SAM-Net framework incorporates the self-attention mechanism as an optimization tool to enhance the ultimate decision-making accuracy of the framework. Thirdly, the BT-SAM-Net framework was compared with 7 other methods. The results show the superiority and stability by demonstrating the BT-SAM-Net framework can identify various aero-pipeline fault states with greater accuracy.

Initial stage of formation of vortex flow in an inductor with counter-rotating magnetic fields

In this article, unsteady flows of electrically conductive fluid in a cylindrical cavity under the action of differently directed rotating magnetic fields are investigated. The relevance of the study is due to the presence of such a flow in the flow meter for liquid-metal heat carrier which is currently under development. The subject of study is the process of formation of the spin-up flow stage in a combined inductor of a rotating magnetic field. The acceleration or the spin-up stage is characterized by a significant change in the angular velocity of the liquid and begins with the formation of low pressure areas due to centrifugal forces. The alternation and movement of low and high pressure areas lead to velocity pulsations. For small values of the control parameter, which is the Taylor number, the flow energy gradually increases. In this case, the steady flow consists of two azimuthal and several poloidal vortices with clearly defined structures. When the Taylor number exceeds a critical value, strong pulsations occur in the flow, resulting in the decay of large-scale vortices. The intensity of the current is characterized by the Reynolds number. A power-law relationship with an exponent of 1.57 has been established between the Reynolds and Taylor numbers. It has been found that the time of formation of a steady flow varies from several seconds to tens of seconds, depending on the value of the Taylor number. The estimates of the control parameters have been obtained for a flowmeter operating in a typical mode. It has been shown that for the correct measurement of flow velocity in the flowmeter, it is necessary that that the Taylor numbers be higher than 108. The study is carried out using mathematical modeling and the obtained results are verified by experiment. The average calculated profiles are located within the confidence intervals of the experimental profiles.

Optimized Model Torque Prediction Control Strategy for BLDCM Torque Error and Speed Error Reduction System

This paper presents an improved whale optimization algorithm (IWOA) for optimizing the model predictive torque control (MPTC) of brushless DC motor (BLDCM) to further reduce the problems of strong torque pulsation and high ripple caused by the special structure of BLDCM. IWOA adds a randomized convergence factor strategy to the original algorithm, enabling the parameter weights to be adjusted in time. The relative error between the training set and the predicted values is reduced, and a suitable interval is selected for the target. The proposed method takes into account the switching frequency loss factor in the MPTC system of BLDCM, discarding the traditional trial-and-error method and choosing to control the parameter adjustment by the degree of deviation. The IWOA is compared with the popular whale optimization algorithm (WOA), dragonfly algorithm (DA), ant colony optimization (ACO) algorithm, and grey wolf optimization (GWO) algorithm on the MATLAB SIMULINK platform to verify the effectiveness of the method in dealing with improved chain tracking, reduced torque pulsation, and reduced speed error. The simulation results show that IWOA performs well, with an efficiency of 94.32%.

Influence of Blade Trailing-Edge Filing on the Transient Characteristics of the Centrifugal Pump during Startup

During the startup process of a centrifugal pump, the vibration and noise problems caused by unsteady flow are the focus of attention, and pressure pulsation is one of the main reasons for this problem. In the current research, a special impeller with blade pressure side trimming was proposed to reduce the strong pressure pulsation phenomenon during the startup process of centrifugal pumps. This article uses numerical simulation methods to simulate three typical blade trailing edges: original trailing edge (OTE), pressure side long linear (LLPS), and pressure side short linear (SLPS), and verifies them with experimental results. The results indicate that although the head of the centrifugal pump after filing has been reduced, its efficiency has been improved to a certain extent. Thirteen monitoring points were set up near the impeller outlet circumference and volute tongue to analyze the changes in pressure pulsation, verifying that blade trimming has a significant inhibitory effect on pressure pulsation during the startup of centrifugal pumps. The average maximum pressure pulsation amplitude of all monitoring points decreased by 32.23%, and the maximum pressure pulsation amplitude decreased by 56%. Blade trimming can affect the internal flow field distribution of centrifugal pumps. By analyzing the static pressure distribution, velocity streamline distribution, and vorticity distribution at the middle interface of three different impellers during startup, it was verified that there is a close relationship between pressure pulsation and unsteady flow structure during startup. The final conclusion is that blade trimming has a significant inhibitory effect on the pressure pulsation of the centrifugal pump during startup, and the impeller outlet vorticity is significantly reduced. The scheme proposed in this study has far-reaching prospects in the design of low noise centrifugal pumps.

Analysis on three-dimensional flow characteristics of rotor wake

As the main lift and control component of helicopters, the rotor has a complex flow field structure with unique characteristics, such as unsteadiness, paddle-vortex interference, and tip vortex. Thus, it is challenging to measure the rotor flow field. In addition, the instability of the flow is accompanied by strong flow pulsation, which leads to noise and blade vibration during the formation of tip vortices. A phase-locked Stereoscopic Particle Image Velocimetry (SPIV) technique, SPIV measurement technology, and phase locked technology are adopted in the present study to investigate the blade tip vortex. The blade tip vortex, which is the main flow structure to be characterized in this study about the rotor wake, is measured by the phase-locked SPIV technique. The velocity and vorticity fields at five phases are presented. Then, the main energetic modes of pulsation were extracted by proper orthogonal decomposition to analyze the instability characteristics of the flow. Finally, the three-dimensional structure of the blade tip vortex is reconstructed and presented. It can be seen that the blade tip vortex has a spiral structure and develops toward the rotor axis.

TESS search for substellar companions through pulsation timing of δ Scuti stars

Early-type main-sequence pulsating stars such as δ Scuti variables are one of the least explored class of targets in the search for exoplanets. Pulsation timing (PT) is an alternative technique to the most effective search methods. It exploits the light-travel-time effect (LTTE) to infer the presence of additional massive bodies around a pulsating star by measuring a periodic phase modulation of its signal. PT has been extremely successful in discovering and characterizing stellar binaries when it was applied to high-precision light curves over long temporal baselines, such as those delivered by the Kepler mission. In favorable conditions, the sensitivity of PT can reach the planetary-mass regime; one such candidate has already been claimed. The advent of TESS, with its nearly full-sky coverage and the availability of full-frame images, opens a great opportunity to expand this field of research. In this work, we present a pilot study aimed to understand the potential of PT as applied to TESS data, which are considerably different from Kepler data in terms of photometric noise, sampling cadence, and temporal baseline. We focused on the most favorable class of δ Scuti, that is, those showing strong pulsations and very simple frequency spectra. After the development of a customized pipeline, we were able to detect candidate companions for two targets in the (sub-)stellar mass regime: Chang 134 (43 ± 5 Mjup, P ≃ 82 days) and V393 Car (≳100 Mjup, P ≳ 700 days). Our results also highlight the limiting factors of this technique and the importance of an accurate absolute time calibration for future missions such as PLATO.

Pulse Timing Discovery of a Three-day Companion to the Hot Subdwarf BPM 36430

Hot subdwarf B stars are core-helium-burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBVrs pulsator exhibiting several low-amplitude g-modes and a strong p-mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 days. Using the CHIRON echelle spectrograph on the CTIO 1.5 m telescope, we confirm the reflex motion by detecting a radial-velocity variation with semiamplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of ≈0.42 M ⊙ orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.

Peculiar temporal and spectral features in highly obscured HMXB pulsar IGR J16320-4751 using XMM-Newton

IGR J16320-4751 is a highly obscured HMXB source containing a very slow neutron star (Pspin∼1300 sec) orbiting its supergiant companion star with a period of ∼9 days. It shows high column density (NH∼2−5×1023cm−2) in the spectrum, and a large variation in flux along the orbit despite not being an eclipsing source. We report on some peculiar timing and spectral features from archival XMM-Newton observation of this source including 8 observations taken during a single orbit. The pulsar shows large timing variability in terms of average count rate from different observations, flaring activity, sudden changes in count rate, cessation of pulsation, and variable pulse profile even from observations taken a few days apart. We note that IGR J16320-4751 is among a small number of sources for which this temporary cessation of pulsation in the light curve has been observed. A time-resolved spectral analysis around the segment of missing pulse shows that variable absorption is deriving such a behavior in this source. Energy resolved pulse profiles in 6.2–6.6 keV band which has a partial contribution from Fe Kα photons, show strong pulsation. However, a more systematic analysis reveals a flat pulse profile from the contribution of Fe Kα photons in this band implying a symmetric distribution for the material responsible for this emission. Soft excess emission below 3 keV is seen in 6 out of 11 spectra of XMM-Newton observations.

Explosion overpressure behavior and flame propagation characteristics in hybrid explosions of hydrogen and magnesium dust

The explosion risk of a hybrid mixture of hydrogen and magnesium dust is relatively high during the production of magnesium-based hydrogen storage materials and industrial magnesium products. To explore the explosion characteristics of a hybrid hydrogen/magnesium dust mixture, the overpressure variation and flame propagation characteristics of the hybrid hydrogen/magnesium dust mixture in a 5-L semi-closed explosion duct were experimentally studied. The results show that the explosion pressure (Pex) and the explosion pressure rise rate ((dP/dt)ex) of the hybrid hydrogen/magnesium dust mixture significantly increase only when the hydrogen concentration is greater than 10 %. The flame of a pure magnesium dust explosion mainly consists of the unburned zone, preheating zone, and combustion reaction zone. Compared with pure magnesium dust, the flame structure of the hybrid hydrogen/magnesium dust mixture explosion does not change significantly, but a red emission zone appears at the front of the preheating zone. Moreover, the range of the preheating zone is significantly larger compared to pure magnesium dust, and it increases with the hydrogen concentration. When the hydrogen concentration is low, the flame propagation speed of the hybrid hydrogen/magnesium dust mixture exhibits strong pulsation. The pulsation frequency of the flame propagation speed of the hybrid mixture explosion gradually decreases with the hydrogen concentration, but the average flame propagation speed continually increases. Based on the experimental results, the explosion mechanism of the hybrid hydrogen/magnesium dust mixture was analyzed from the perspective of reaction kinetics by numerical simulation.

How angular-momentum flux controls Francis turbine full-load surge

Hydropower plants equipped with Francis turbines may enter unstable conditions at high turbine discharge [13], with strong pulsations of power output and internal pressure. The cause are oscillations of a vapor-filled cavity in the vortex flow downstream of the turbine runner, interacting with the draft tube and penstock pressure. The paper describes the structure and simulation results of a 1D distributed-parameter model for full-load surge, parametrized from results of a high-resolution unsteady two-phase CFD simulation study (Wack [14]) of high-load pulsations in the reduced-scale model of a medium-specific speed Francis turbine. In earlier research on the same model turbine, Müller [12] had suggested that runner blade cavitation could cause instability. To clarify this, variation of turbine intake flow was sup-pressed, and the influence of pressure variation via runner blade cavitation on the relative runner exit flow angle and angular-momentum flux was simulated. Due to the upstream boundary condition, the influence of mass-flow gain χ is replaced by a cavitation gain factor ψ, likewise delayed by the limited speed of swirl propagation. It is found that gain factors obtained from steady-state simulation cannot be directly used with a lumped-parameter model because the swirl effect is much reduced due to its phase changes along the vortex; using the steady-state gain factors would thus exaggerate the influence of swirl on cavity volume. Simulation in frequency domain with realistic swirl transport delay confirms that instability can occur because in some parts of the cavitation zone the swirl provides oscillation power.

Temporal and Spatial Analysis on the Fractal Characteristics of the Helical Vortex Rope

Vortex rope is a common phenomenon in the draft tube of hydraulic turbines. It may cause strong pressure pulsation, noise, and strong vibration of the unit especially when it is helical. Therefore, the study of vortex rope is of great significance. In order to study the helical vortex rope, the embedded large eddy simulation (ELES) method in the hybrid methods is used based on the vortex rope generator case. The Liutex method can show the three-dimensional shape of the vortex rope well. In order to quantitatively describe the helical vortex rope, the three-dimensional structure is divided into multiple two-dimensional sections, and then the shape of vortex rope on each section is processed to extract the perimeter and area of the vortex. Combined with the change trend of vortex number and section area, the helical vortex rope is divided into four zones. Then, the fractal dimension on each zone and section can be obtained, and it can be used to quantitatively analyze the change trend of the vortex rope in time and space. The fractal analysis method can be applied to the analysis of the vortex rope in the draft tube to help judge the flow pattern shape and the stability of the unit operating conditions.

Spatial distribution and transient evolution of sub-droplet velocity and size in ultrasonic atomization

Ultrasonic atomization has been applied widely in various industrial fields because of its excellent atomization uniformity and high material utilization. The performance and quality of the final product greatly depend on the atomization characteristics, such as droplet velocity and droplet size distribution. The present work experimentally investigated the atomization characteristics of a single droplet using an ultrasonic atomizer. The influence of the vibration amplitude on the atomization characteristics was studied. The microscopic and macroscopic atomization processes were analyzed with backlight photography and particle image velocimetry (PIV) respectively. The atomization angle and the overall velocity field under different vibration amplitudes were quantitatively determined. We studied the transient velocity distribution evolution (the velocity along the axis, the radial distribution of the vertical and the horizontal velocity) of atomized droplets and the corresponding droplet size distribution for the first time, and established the dimensionless correlation analysis between the two. The characteristics of the time-averaged velocity, velocity pulsation, vorticity, and Reynolds stress during atomization were also demonstrated. Results show that the atomization angle and the overall velocity of the atomization field suggest strong transient and pulsation. The position of the velocity peak is closer to the vibrating head as the amplitude increases. The transient distribution evolution of the vertical velocity and the droplet size has strong consistency and the new dimensionless correlation for the two shows a high fitting. The horizontal velocity is zero at the central axis, and the value increases with the increase of the radial distance. The increase in vibration amplitude makes the atomization process more explosive. This work will provide practical data and scientific guidance for the controllability and optimization of ultrasonic atomization performance.

Analysis of Runner Dynamics of Reversible Hydraulic Turbine by Alternating Fluid–Solid Action

In order to study the effect of alternating fluid–solid action on the dynamic characteristics of the runner of a reversible hydraulic turbine, a reversible hydraulic turbine model is used as the research object, and the two-way fluid–solid coupling method is used to iteratively calculate and analyze the fluid and structural equations to obtain the effect of the reversible hydraulic turbine on the runner under the two-way fluid–solid coupling action of the runner of the reversible hydraulic turbine under typical operating conditions. The results showed that under the influence of a high-speed water ring area under a certain working condition, the incoming flow direction forms a certain impulse angle with the blade, and under the joint action of the runner rotating at high speed, the vortex structure is generated in the blade area, and the speed change in the inlet area has a large random fluctuation, which is not conducive to the stability of the runner area and causes a strong pressure pulsation at the inlet. Under different working conditions, the runner stress area phenomenon is obvious, concentrated in the runner blade inlet side and the upper crown, lower ring connection. The maximum deformation region appears in the lower region of the middle of the blade inlet. The comparison of the modal analysis shows that the dynamic stress frequency caused by the dynamic interference is very unlikely to trigger the resonance of the runner.

Quantitative visualization of injection jet flow behaviors of transcritical and supercritical processes by pixelated phase-shifting interferometer

Precise measurement and visualization of trans-/supercritical jet processes are of great significance for the control of power engines, chemical reaction and industrial processes. The quantitative measurement of transcritical jet under the influence of high pressure effect and transient effect is the key issues in such analysis. In this study, an improved phase-shifting interferometer system with high temporal and spatial resolution (0.001 s, 3.45 μm) has been realized by pixelated-array masked method to investigate characteristics in trans/supercritical jet processes. The transient density field and boundary structure of the phase-transition interface during four jet processes under sub/trans/supercritical conditions were quantitatively measured, which is different from those under subcritical conditions. The results show that the characteristic of subcritical jet is phenomenon of fragmentation and atomization within the experimental cell due to the presence of interfacial tension and strong density pulsations. The atomization is suppressed by high pressure effect in supercritical jet. Instead, Instead, single-phase mixing occurs due to the absence of surface tension. The dense core is found gradually dissolved during diffusion process of the jet flow. The transition from liquid-like to gas-like status of fluid occurs when the injection fluid goes cross the pseudo-critical line, and the jet surface has a large density gradient (in the current test range, |∇ρ|max = 8 × 105 kg/m4) due to temperature rise and pseudo-boiling expansion.

Discovery of a pulse-phase-transient cyclotron line in the X-ray pulsar Swift J1808.4−1754 and identification of an optical companion

ABSTRACT In this work, the temporal and spectral properties of the poorly studied X-ray pulsar Swift J1808.4−1754 were investigated in the 0.8–79 keV energy range based on the data from the NuSTAR and Swift observatories collected during the 2014 outburst. Strong pulsations with a period of 909.73 ± 0.03 s were detected in the source light curve, with the pulsed fraction demonstrating a non-monotonic dependence on the energy with a local minimum around 17–22 keV. Phase lags in one of the pulse profile components, reaching the maximal value approximately at the same energy, were discovered. The pulse phase-averaged spectrum of the source has a power-law shape with an exponential cutoff at high energies, which is typical of X-ray pulsars. Pulse phase-resolved spectroscopy revealed the presence of a pulse-phase-transient cyclotron absorption line at ∼21 keV, allowing us to estimate the neutron star magnetic field of 2.4 × 1012 G. This makes Swift J1808.4−1754 a member of very small family of X-ray pulsars with a pulse-phase-transient cyclotron line in a narrow phase range. The data from the Nordic Optical Telescope allowed us to study the properties of the infrared companion in the system and to conclude that most probably it is a Be-type star located at a distance of 5–8 kpc.