Transient Flow Phenomena Research Articles

Computational Fluid Dynamics Process for Front Windshield Mist Deposition and Its Subsequent Demisting

<div>A vehicle’s heating, ventilation, and air-conditioning system plays a dual role in passenger thermal comfort and safety. The functional aspects of safety include the front windshield demist and deicing feature of the system. The thin-film mist is a result of condensation of water vapor on the inner side of the windshield, which occurs at low ambient temperatures or high humidity. This mist deposition depends on the air saturation pressure at the front windshield. Indian regulation AIS-084 defines the experimental setup for testing, which encompasses both the mist deposition and its subsequent demist process. This regulation mandates testing, which occurs at a later stage of product development. This performance validation can be performed using a three-dimensional computational fluid dynamics approach.</div> <div>Current work summarizes the simulation process for both the mist deposition and the subsequent demisting phenomenon. The complexity of the flow physics is captured via the transient multiphase fluid flow phenomenon subjected to buoyancy effects. This phenomenon is simulated using the Eulerian wall film approach. The wall film deposition of the mist is modeled via species transport. Further, the near-wall thermal effects of surface conduction and heat transfer are simulated by modeling shell conduction layers. Vapor diffusion and relative humidity inside the cabin are modeled using a user-defined function. The process correlation is achieved for two categories of vehicles to establish the process efficacy and robustness. Moving ahead, a design of experiments (DOE) is planned to mitigate the need to simulate mist deposition. The DOE is planning to incorporate deviations in both the input airflow conditions and the imposed ambient conditions. The results from DOE point toward factors that might cause deviations in simulation results with respect to the test. Importantly, the study concludes that the uniform initial thickness assumption of the mist layer can be used for subsequent demist analysis.</div>

Case Study: Innovative Sand-Screen Technology Resolves Offshore Nigeria Water-Injection Issues

_ During continuous injection, reservoir solids usually remain within the reservoir. However, prolonged or abrupt well shut ins can trigger intense transient flow phenomena like water hammer, backflow, and crossflow, causing fines and matrix sands to migrate and accumulate in the wellbore (SPE 187103). As a result, the accumulation of debris can markedly reduce structural integrity and the overall long-term viability of enhanced oil recovery (EOR) from the injection wells. This issue had become particularly evident in an offshore field situated in the southern region of the Niger Delta. Over time, buildup in the well led to a substantial decrease in injection rates, which had significantly shortened the operational lifespan of the wells to just a few years at the anticipated injection rates. Various remediation technologies were attempted, such as tubing-installed valve and backflow-restrictor technology but both proved ineffective in resolving annular-flow and crossflow issues. To prevent potentially expensive and complex interventions, sidetracking, or wellbore abandonment, further analyses by the operator, SNEPCo, concluded that an effective solution necessitated deployment as close to the sandface within the injector wells as possible. The Cascade system, a check-valve system developed by TAQA Well Completions (formerly Tendeka), was then successfully deployed in three wells to maintain the required injection volumes for efficient pressure maintenance and reservoir sweep. Non-Return Valve Screen Technology Establishing a reliable flow-control system for the lower completion requires engineering the check-valve components to seamlessly integrate within the sand-control screens for deployment across multiple zones of the injection tubing. The non-return valve (NRV) employs a three-component design comprising a valve body, valve insert, and ball. Ball check valves are installed on the screen base pipe under a shroud that allows the injection of fluid into the reservoir and prevents any backflow from the reservoir during shut ins. The system features a flow-control check valve integrated within traditional sand screens that do not alter completion geometry (Fig. 1). With a metal-to-metal seal, it essentially isolates fluid in the completion annulus and locks injection water into the formation. The NRV has been designed to handle a variety of well conditions including erosion, plugging, temperature, and repeated checking cycles. All flow-control device components are manufactured with high-alloy stainless steel and tungsten carbide components to resist tortuous downhole conditions for up to 15 years. Developed in 2018, more than 2,000 of the valves have already been successfully installed in several wells globally. As this new sand-control technology can autonomously and immediately isolate the reservoir from the wellbore during shut ins, the technology offers additional benefits. - Nonintrusive nature for intervention tools - Unhindered access to the lower completion sandface during injection and intervention - Durability throughout the well’s operational life - Compatibility with openhole standalone screens, gravel- pack completions, direct wrap or metal mesh screens - Cost-effectiveness compared to other options

Transient gas-liquid flow phenomena in M-shaped jumper of subsea gas production systems during start-up operation

Removal of the accumulated liquid from jumpers of subsea gas production systems is essential to avoid possible hydrate creation and further damage to the pipeline. However, the displacement of high amounts of accumulated liquid during the production start-up leads to a gas pressure rise. Liquid plugs formed during the liquid displacement impact the structure's elbows. This, in addition to cyclic pressure/forces fluctuations, may lead to harmful flow-induced vibrations (FIV). These flow phenomena that may endanger the jumper structure were explored in air-water experiments performed in a lab-scale jumper. The critical (minimal) gas velocity needed to purge the accumulated liquid was determined and the pressure and force variations during the liquid removal were measured. In addition, the effects of the gas velocity, initial liquid amount, and gas flow ramp-up on the air-water flow phenomena were documented. Results of 3D and 2D numerical simulations (using OpenFOAM) were verified against the experimental data. The effects of employing different RANS turbulence models on the predictions were tested and demonstrated. A simple mechanistic model was established to predict the pressure and force variation during liquid displacement. The model enables inspecting the variation with the operational conditions of each pressure component (i.e., hydrostatic, friction, and acceleration) and examining their significance and contribution to the pressure rise.

A Composite Framework Model for Transient Pressure Dynamics in Tight Gas Reservoirs Incorporating Stress Sensitivity

Natural gas is an eco-friendly energy source with low carbon emissions, making it attractive globally. Understanding gas reservoirs is crucial for sustainable extraction and optimizing potential. However, the complicated fluid flow and production dynamics within intricate gas reservoirs, particularly those characterized by abnormally high pressures and tight porous media, remain partially understood and demand further investigation. In a tight porous medium subjected to high pressure, the assumption of constant permeability is no longer valid. Consequently, a novel composite seepage model has been developed in this study, which considers the responsiveness of permeability to stress. Perturbation theory is employed to address the inherent non-linearity demonstrated by the permeability modulus. The solution of dimensionless pressure responses under constant production conditions is accomplished in the Laplace domain by implementing integral transformation methods. Overall, a comprehensive model is provided to understand the production behaviors of tight gas reservoirs. Moreover, in order to comprehend the transient flow characteristics of tight gas reservoirs, log–log plots are generated through the Stehfest numerical inversion approach, with the flow regimes categorized based on the normalized time phases of the pressure curves. Parametric investigations reveal that stress sensitivity detrimentally affects permeability, resulting in more pronounced pressure declines during the intermediate and late flow phases. The transient seepage model elaborated in this study is able to consider the pertinent formation and well parameters. These interpreted parameters bear significance in designing hydraulic fracturing operations, assessing the potential of tight gas reservoirs, and ultimately enhancing gas production. The presented model not only enhances our understanding of the behavior of horizontal wells in stress-sensitive tight gas reservoirs but also makes a valuable contribution to the broader discussion on transient flow phenomena in petroleum engineering.

Experimental Investigation of Transient Flow Phenomena in Rotating Compressor Cavities

Abstract The clearance of compressor blade tips during aero-engine accelerations is an important design issue for next-generation engine architectures. The transient clearance depends on the radial expansion of the compressor discs, which is directly coupled to conjugate heat transfer in co-rotating discs governed by unsteady and unstable buoyancy-induced flow. This paper discusses an experimental and modeling study using the Bath Compressor Cavity Rig, which simulates a generic axial compressor at fluid-dynamically scaled conditions. The rig was specifically designed to generate heat transfer of practical interest to the engine designer and validate computational codes. This work presents the first study of the fundamental fluid dynamic and heat transfer phenomena under transient conditions. The rotating flow structure was seen to be characterized by coherent pairs of cyclonic/anticyclonic vortex pairs; the strength, rotational frequency, stability, and number of these unsteady structures changed with changing rotational Reynolds and Grashof numbers during the transients. These structures, measured by unsteady pressure transducers in the rotating frame of reference, were only present when the flow in the rotating cavity was dominated by buoyancy. Experimental correlations of both Nusselt number and radial mass flowrate in the rotating core were correlated against Grashof number. Remarkably, the experiments revealed a consistent correlation for both steady-state and transient conditions over a wide range of Gr. The results have a practical application to thermo-mechanical models for engine design.

Transient simulation of melt flow, clogging, and clog fragmentation inside SEN during steel continuous casting

Clogging of submerged entry nozzle (SEN) during continuous casting of steel is an undesirable phenomenon leading to different problems like flow blockage, slag entrainment, nonuniform solidification, etc. A transient numerical model for nozzle clogging based on an Eulerian-Lagrangian approach was developed and it covers the main steps of clogging: (a) formation of the first oxide layer by chemical reactions on the steel-refractory interface; (b) motion of non-metallic inclusions (NMIs) due to the turbulent melt flow towards the SEN wall; (c) interactions between the melt, the NMI, and the wall; (d) formation and growth of the clog by the deposition of NMIs on the clog front and the flow-clog interactions; and (e) detachment/fragmentation of a part of clog due to the flow drag force. Clogging in an industrial scale SEN was simulated. The simulated clog front was compared with real as-clogged SENs. The modeling results have successfully explained the SEN clogging induced transient flow phenomenon in the mold region, i.e. the transition from the stable to an unstable and non-symmetrical flow.

Experimental investigation of pressure fluctuation and steam transport under SGTR accident in Lead-cooled Fast Reactors

Transient multiphase flow phenomenon of hyperbaric water jetting into lead-based eutectic (LBE) is of significant importance for safety analysis of Lead-cooled Fast Reactors (LFRs). In order to investigate the thermal-hydraulic parameters under Steam Generator Tube Rupture (SGTR) Accident in LFRs, the Lead-bismuth Eutectic Steam generator tube rupture Test facility (LEST) was built and the effects of (1) initial pressure peak, (2) pressure rising, (3) steam cavity migration in reaction vessel were evaluated. Under the present experimental and theoretical analysis, the results showed that the maximum pressure peak of 2.93 MPa occurred under the condition of 10 MPa water initial pressure which is the highest experimental requirements of reactor second system, and the accident consequence of pressure peak together with the maximum rising rate 2.001 MPa/s might be the most serious. Floating rate of steam cavity was different in radial direction, and was affected by water pressure and LBE level height. The analysis results will provide severity assessment for safety design, accident forecasting and engineering guidance of LFRs.

4-dimensional local radial basis function interpolation of large, uniformly spaced datasets

Background and ObjectiveLarge, uniformly spaced, complex and time varying datasets derived from high resolution medical image velocimetry can provide a wealth of information regarding small-scale transient physiological flow phenomena and pulsation of anatomical boundaries. However, there remains a need for interpolation techniques to effectively reconstruct a fully 4-dimensional functional relationship from this data. This paper presents a preliminary evaluation of a 4-dimensional local radial basis function (RBF) algorithm as a means of addressing this problem for laminar flows. MethodsA 4D interpolation algorithm is proposed based on a Local Hermitian Interpolation (LHI) using a combination of multi-quadric RBF with a partition of unity scheme. The domain is divided into uniform sub-systems with size restricted to immediately neighbouring points. The validity of the algorithm is first established on a known 4D analytical dataset and a CFD based laminar flow phantom. Application is then demonstrated through characterisation of a large 4D laminar flow dataset obtained from magnetic resonance imaging (MRI) measurements of cerebrospinal fluid velocities in the brain. ResultsPerformance of the algorithm is compared to that of a quad-linear interpolation, demonstrating favourable improvement in accuracy. The technique is shown to be robust, computationally efficient and capable of refined interpolation in Euclidean space and time. Application to MR velocimetry data is shown to produce promising results for the 4D reconstruction of the transient flow field and movement of the fluid boundaries at spatial and temporal locations intermediate to the original data. ConclusionThis study has demonstrated feasibility of an accurate, stable and efficient 4-dimensional local RBF interpolation method for large, transient laminar flow velocimetry datasets. The proposed approach does not suffer from ill-conditioning or high computational cost due to domain decomposition into local stencils where the RBF is only ever applied to a limited number of points. This work offers a potential tool to assist medical diagnoses and drug delivery through better understanding of physiological flow fields such as cerebrospinal fluid. Further work will evaluate the technique on a wider range of flow fields and against CFD simulation.

Hydraulic Jump Behavior during Filling Process of Cast Start II

This paper presents a 0.25-scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel under solidification. Water cooling is performed at the bottom of the mold, and saturated sodium acetate solution is covered on the spring and particle arrangement at the bottom of the mold/on the dummy bar to simulate the solidification phenomenon in the actual continuous casting process. The results show that the solidification on the dummy bar surface is very important to the early stage of the filling process and cannot be ignored. Its influence gradually decreases with the rise of the liquid level, and basically disappears when the liquid level rises to a certain height (steady liquid level, SLL). In SLL, the interface morphology of the solidified layer is more affected by the flow, while the interface morphology of the solidified layer has no significant effect on the liquid surface velocity.

Hydraulic Jump Behavior during Filling Process of Cast Start I

This paper presents a 0.25 scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel. The relationship between the continuous casting process and the hydraulic jump phenomenon is established. The casting process in the mold is divided into four stages (I–IV) from the beginning to the end of continuous casting. The filling process involves stages I–II and is investigated by high-speed camera. The filling process is part of the cast start. In this paper, the hydraulic jump behavior varies and is controlled by different spring and iron chips arrangement on the dummy bar during the filling process. A filling coefficient is proposed to judge the best filling conditions and apply them to the whole filling process. There is an optimal spring and iron chip arrangement, which can adjust the hydraulic jump to optimize the initial flow field during the filling process, even the whole continuous casting process.

Dynamically Coupled Reservoir and Wellbore Simulation Research in Two-Phase Flow Systems: A Critical Review

A coupled reservoir/wellbore simulator is essential for solving relevant flow phenomena with dynamic interactions between reservoir and wellbore in two-phase flow systems. A reservoir simulator or wellbore simulator alone fails to solve these transient flow phenomena. This paper summarises a critical review of the coupled reservoir and wellbore simulation. First, a wide application of the drift-flux (DF) models to simulate gas–liquid flow in a wellbore model coupling to a reservoir model was discussed. Then, the mechanisms of the coupled reservoir/wellbore simulator in two-phase flow systems were discussed, including the reservoir modeling, wellbore modeling, and their coupling schemes. Various examples of representative coupled simulators were presented. Finally, some case studies were reported to reveal dynamic interactions between wellbore and reservoir by using the coupled reservoir/wellbore simulators. This study gives the most up-to-date and systematic sights on the relevant research topic of reservoir/wellbore coupling, allowing for a better understanding of the coupled reservoir and wellbore simulation and its application in the oil and gas industry.

Boltzmann transformation of radial two-phase black oil model for tight oil reservoirs

Tight oil accumulates in impermeable reservoir rocks, often shale or tight sandstones. The flow behaviour of tight oil in unconventional reservoirs is described by peculiar complexities such as the typical low permeability to viscosity ratio and the dissolution of some gases in the oil phase. Reservoir simulations that consider these complexities negligible stand the potential of poorly characterizing the reservoir flow dynamics. The adoption of similarity transformation effectively reduces the complexities associated with the flow equations through spatial variable (r) and temporal variable (t). The Boltzmann variable left(xi =dfrac{r}{sqrt{t}}right) is introduced to facilitate the reformulation of transient two-phase flow phenomenon in a radial geometry. The technique converts the two-phase Black oil model (thus highly nonlinear partial differential equations (PDEs)) to ordinary differential equations (ODEs). The resulting ODEs present a reduced form on the flow model which is solved by finite difference approximations (the Implicit-Pressure-Explicit-Saturation (IMPES)) scheme. No loss of vital flow characteristics was observed between the Black oil model and the similarity transform flow model. Furthermore, the similarity approach facilitated the determination of pressure and saturation equations as unique functions of the Boltzmann variable. This derivation is applied to an infinitely acting reservoir where the Boltzmann variable tends to infinity (xi rightarrow infty). Finally, this case study’s analytical solution formulated critical relations for fluid flow rate and cumulative production, which are useful for single-phase flow analysis.

Numerical and experimental study of the transient conjugate heat transfer and fluid flow of passive residual heat removal heat exchanger

The transient heat transfer performance of passive residual heat removal heat exchanger (PRHR HX) with C-tube bundle directly influences nuclear reactor safety under accident condition. This paper presents an investigation of transient conjugate heat transfer and fluid flow phenomena and characteristics of scaled-down single C-tube submerged in water tank under atmospheric pressure at the initial period before saturation pool boiling occurs. Empirical calculation model, experimental setup and numerical model were established separately, and both numerical and experimental studies were carried out. The distributions of tube outlet temperature and water temperatures at horizontal and vertical monitoring points in tank were obtained. Detailed comparisons of the results show good agreements. Also, the change tendencies of heat flux, heat transfer coefficients and heat load were analyzed. The fluctuation of heat flux along normalized length from tube inlet firstly increases but finally tends to keep stable with the change of temperature difference and transformation of heat transfer mechanism. The heat transfer coefficient inside tube shows a slight downtrend along normalized length from tube inlet, but the heat transfer coefficient outside tube shows obvious change in the transient process. The total heat load continuously decreases with time. Furthermore, the volume fraction of vapor is relatively low during the subcooled boiling period. The two-phase flow enhances the agitation in water tank and the fluid velocity near tube outside wall is much larger.

Numerical Simulation and Experimental Validation of a Kaplan Prototype Turbine Operating on a Cam Curve

The role of hydropower has become increasingly essential following the introduction of intermittent renewable energies. Quickly regulating power is needed, and the transient operations of hydropower plants have consequently become more frequent. Large pressure fluctuations occur during transient operations, leading to the premature fatigue and wear of hydraulic turbines. Investigations of the transient flow phenomena developed in small-scale turbine models are useful and accessible but limited. On the other hand, experimental and numerical studies of full-scale large turbines are challenging due to production losses, large scales, high Reynolds numbers, and computational demands. In the present work, the operation of a 10 MW Kaplan prototype turbine was modelled for two operating points on a propeller curve corresponding to the best efficiency point and part-load conditions. First, an analysis of the possible means of reducing the model complexity is presented. The influence of the boundary conditions, runner blade clearance, blade geometry and mesh size on the numerical results is discussed. Secondly, the results of the numerical simulations are presented and compared to experimental measurements performed on the prototype in order to validate the numerical model. The mean torque and pressure values were reasonably predicted at both operating points with the simplified model. An analysis of the pressure fluctuations at part load demonstrated that the numerical simulation captured the rotating vortex rope developed in the draft tube. The frequencies of the rotating and plunging components of the rotating vortex were accurately captured, but the amplitudes were underestimated compared to the experimental data.

Influence of transient heat flux on boiling flow pattern in a straight microchannel applied in concentrator photovoltaic systems

Concentrated photovoltaic (CPV) overheating due to the high radiation intensity became the critical challenge to preventing its benefits in advancing the photoelectric efficiency. To promote the application of CPV, efficient heat dissipation becomes the key technology. Meanwhile, microchannel flow boiling, as one of the most promising solution to advance cooling of high-flux equipment, has attracted increasing attentions in recent years. However, the fluctuating and non-uniform heat fluxes of CPVs may lead to challenges to microchannel boiling for cooling CPV. Therefore, the transient flow and phase change phenomenon in a microchannel with deionized (DI) water was studied through a numerical modeling on flow boiling. The effects of different sudden heat flux increases on flow boiling two-phase flow pattern were analyzed. It was found that different heat flux increase resulted to different flow pattern evolutions, a much higher sudden increase in heat flux leaded to serious variation of flow pattern, especially the fluctuation of elongated restricted bubbles, which may evolve to annular flow or even dry-out. The vapor phase volume fraction showed a much higher growth rate. When the heat flux increase was raised from 97.96 kW/m2 to 580 kW/m2, the maximum vapor phase volume fraction was increased from 0.104 to 0.8064, and the bubble length increased from smaller than 0.3 mm to 1.5 mm in the dry zone, indicating rapid phase change. Based on analysis on pressure drop and vapor volume fraction variation, the period after receiving sudden heat flux was divided into three stages: initial period, rapid development period, and quasi-stable period. With the rising of heat flux increase from 97.96 to 580 kW/m2, the duration of rapid development period was increased from 0.03 s to 0.066 s, the pressure drop increase was obviously enlarged, from 2.43 kPa to 14.51 kPa, and the vapor phase volume fraction increase in the microchannel was raised by 3.3 times to 25.6 times, indicating more intensive boiling, and deeper effect of higher heat flux increase on the phase change. In addition, the fluctuation intensity of pressure drop in the quasi-stable period was obviously increased from 0.025 to 0.193, demonstrating the advancement in flow boiling instability under higher heat flux increase, which should be controlled.

Coupling of pore network modelling and volume of fluid methods for multiphase flow in fractured media

Modelling multiphase flow in fractured media is a challenging multi-disciplinary problem which is of particular importance for the production of hydrocarbons from unconventional geological formations. At the pore-scale, this can be studied using pore network models that are computationally efficient due to the employment of pore-space geometrical simplifications. There are two distinctive approaches to pore network modelling: quasi-static and dynamic. However, only dynamic pore network models allow capturing the transient nature of the multiphase flow. Nevertheless, the dynamic models have a number of limitations including numerical oscillations and the inability of interface tracking in a particular network element. In order to overcome these drawbacks, a hybrid numerical method which combines the Hagen–Poiseuille analytical solution of the Navier–Stokes equations and the volume of fluid advection scheme is developed and validated. The proposed multiphase model is benchmarked against the conventional volume of fluid implementation for various drainage and imbibition cases using two-dimensional demo cases. Besides, three-dimensional simulations are also performed to ensure the applicability of the proposed model to real fractured media. The single pressure algorithm is employed while the capillary pressure drop is explicitly introduced as an additional term in the Hagen–Poiseuille equation. The conducted validation and following analysis show the applicability of the developed model for a wide range of Reynolds and capillary numbers and viscosity ratio. Thus, the new model can be used to investigate transient immiscible multiphase flow phenomena in fractures by pore network modelling.

A limiter free adaptive THINC-BVD scheme with AUSMV numerical flux for solving the drift flux model

In this article, adaptive THINC-BVD (Tangent of Hyperbola for Interface Capturing)-(Boundary Variations Diminishing) numerical scheme with AUSMV (Advection Upstream Splitting Method based on flux vector splitting) numerical flux is developed for solving the two-phase drift flux model. The drift flux model is considered for analyzing the transient two-phase flow phenomenon in the pipe-lines. This model comprises the two mass conservation equations, one for each phase, and a momentum equation for the mixture of both phases. The mixture momentum equation contains the non-conservative terms. Further, for computation purpose, thermodynamic and hydrodynamic sub-models are considered to close the drift flux model. These non-conservative terms and sub-models offer difficulties in designing the efficient numerical schemes. In the considered adaptive numerical scheme, THINC functions are used for the spatial reconstruction and BVD algorithm is used to minimize the large variations of reconstructed variables at the cell-interfaces. Thus, the developed numerical scheme has great potential to resolve the sharp discontinuities in an efficient and simple way. Various benchmark test problems are considered to verify the robustness of developed adaptive numerical scheme.

Transient Energy Analysis in Water-Filled Viscoelastic Pipelines

AbstractThe transient flow phenomenon in a pipeline accounts for the flow variations with time and space. The transient energy analysis (TEA) overlooks the process as it sums the energy of the enti...

Dynamic-stall measurements using time-resolved pressure-sensitive paint on double-swept rotor blades

The study presents an optimized pressure-sensitive paint (PSP) measurement system that was applied to investigate unsteady surface pressures on recently developed double-swept rotor blades in the rotor test facility at the German Aerospace Center (DLR) in Göttingen. The measurement system featured an improved version of a double-shutter camera that was designed to reduce image blur in PSP measurements on fast rotating blades. It also comprised DLR’s PSP sensor, developed to capture transient flow phenomena (iPSP). Unsteady surface pressures were acquired across the outer 65% of the rotor blade with iPSP and at several radial blade sections by fast-response pressure transducers at blade-tip Mach and Reynolds numbers of mathrm {M}_mathrm{tip} = 0.282-0.285 and mathrm {Re}_mathrm{tip}= 5.84-5.95 times 10^5. The unique experimental setup allowed for scanning surface pressures across the entire pitch cycle at a phase resolution of {0.225},{mathrm{deg}} azimuth for different collective and cyclic-pitch settings. Experimental results of both investigated cyclic-pitch settings are compared in detail to a delayed detached eddy simulation using the flow solver FLOWer and to flow visualizations from unsteady Reynolds-averaged Navier–Stokes (URANS) computations with DLR’s TAU code. The findings reveal a detailed and yet unseen insight into the pressure footprint of double-swept rotor blades undergoing dynamic stall and allow for deducing “stall maps”, where confined areas of stalled flow on the blade are identifiable as a function of the pitch phase.Graphical abstract

Simplified Steady-State Representation of Slot Synthetic Jet Actuators to Enable Numerical Optimization With Steady RANS Simulations

To address the growing energy use of data centers, waste heat recuperation offers a solution to better integrate these facilities into the broader energy system, thus facilitating a transition to the decarbonization of the energy system. The use of liquid coolants for full immersion cooling or local heat extraction from high power density components is considered for this purpose. However, heat can also be extracted by novel air cooling approaches, perhaps in combination with localized liquid cooling. To optimize heat extraction from air-cooled systems and maximize the heat grade, synthetic jets (SJs) can be used for targeted adaptive cooling in conjunction with air ducting to facilitate maximum heat recuperation potential in rack or server-mounted air-to-liquid heat exchangers. Internal server layouts can be optimized numerically, e.g., using a multiple objective genetic algorithm approach based on minimization of entropy generation rates. However, since SJs are inherently transient flow phenomena, this would require transient flow simulations, which forms a bottleneck in a numerical optimization loop. This research aims to develop a simplified steady-state representation of a synthetic jet actuator (SJA) with slot orifice using a localized body force to generate a similar time-averaged flow field to a real SJA, suitable for steady Reynolds-averaged Navier–Stokes simulations within a numerical optimization loop. Both flow fields are compared in terms of the mean flow field, jet spreading rate, and turbulence intensity distributions.