Unsteady Fluid Research Articles

Aerodynamic energy consumption analysis of divided evacuated tube transportation system

Evacuated Tube Transportation (ETT) reduces aerodynamic drag and energy consumption by lowering gas pressure around high-speed trains (HSTs). To optimise this effect, integrating the ETT system into high-speed cruise segments is a practical approach, though it may introduce vacuum potential energy losses. To address this, the paper put forward a Divided Evacuated Tube Transportation (D-ETT) system to seamlessly connect open-line and tube operation of HST then the regulations of aerodynamic energy consumption were studied. Theoretical discussions into reasonable parameter range including tube design and HST operation manners were conducted and then formed system-designing strategy. The spatial and temporal distribution law of tube gas circumstances were examined through model testing and numerical simulation. Three-dimensional, unsteady and compressible fluid models were established using Large Eddy Simulation (LES) to analyse tube fluid characteristics. Relative results indicated that under reasonable D-ETT designing strategies with larger blockage ratios, higher HST speeds, larger total mileage and mileage ratio of the mid-section, the aerodynamic energy saving effect is more impressive. The mixing of the adjacent tube gases with differential pressure induced gas-mixing fluctuations then changed the fluid circumstances inside the tube. The positional relationship between HST and gas waves infected aerodynamic energy consumption. By figuring out the spatiotemporal variation of tube gas, the theoretical energy estimation scheme for aerodynamic energy consumption with various cases was put forward, then the rationality and accuracy of which was verified by numerical simulation with prediction error less than 8%. The saving ratio of aerodynamic drag energy consumption of a 10 km tube could be 39.9% compared to traditional tunnels, which will be higher under ultra-long mileage, thus realising the overall aerodynamic energy saving effect. High-amplitude pressure waves intensified the pressure changes around HSTs, making it necessary to use HST capsules with superior sealing performance to ensure eardrum comfort.

Estimating infectious disease transmission risk: An analysis based on multi-scale modeling of respiratory droplet transport

In the present work, a multi-scale model is used to simulate the trajectory of exhaled droplets for different types of respiratory events. By estimating the saliva viral content, information on the exhaled droplet trajectory and size distribution are exploited to derive spatial maps of viral concentration. The maps are used to estimate the risk of infection by direct inhalation for a susceptible individual exposed to exhalations. Discriminating between the droplets falling to the ground and those remaining airborne, further estimates of the risks associated with fomite and airborne transmission routes are made possible. Simulations are based on an analytical model, recently developed by the authors, implementing the equations of droplet transport, evaporation, energy, and chemical composition. Turbulent dispersion is modeled with a random walk approach, whereas the droplets are released randomly within the exhalation time span and mouth/nose orifice cross section. Droplet transport within the respiratory cloud, a critical aspect in this kind of investigation, is evaluated by coupling the analytical model to the results of unsteady computational fluid dynamics simulations of the respiratory scenarios investigated, namely: mouth breathing, nose breathing, speaking, coughing, and sneezing. Results are compared to those obtained in a previous work where the respiratory cloud was simulated through a two-dimensional unsteady empirical model proposed by the authors based on momentum conservation. The multi-scale model provides better predictions of small droplet trajectories albeit at a higher computational cost. The risk maps provided constitute a useful tool for assessing prevention needs in controlling the spread of epidemics.

Unsteady MHD micropolar fluid flow over a vertical stretching sheet under the influences of radiation, Joule heating and Soret effects in porous medium

The aim of the study is to analyse the combined effect of thermal radiation, Joule heating, thermal diffusivity and heat source on an unsteady MHD flow of micropolar fluid over a vertical stretching sheet in a porous medium. Buoyancy forces, viscous dissipation and higher-order chemical reactions are also taken into consideration. Governing equations are solved by applying the bvp4c technique. The influence of pertinent parameters on the fluid velocity, angular velocity, temperature and concentration is discussed and displayed with the help of their graphical representation. To assess the accuracy and validity of the current study, the results are compared with some previous outcomes and seen as a good agreement with those results. The results divulge that the angular velocity decreases with the increment in the values of the unsteadiness parameter while the opposite behaviour is noticed for fluid velocity, temperature and concentration. In addition, thermal radiation, Joule heating and heat source have a tendency to enhance the fluid temperature. This study advances our knowledge of complex fluid dynamics in porous media, and the tests described in the article can be used to investigate human and animal blood, fuel industries, polymer production, solar collection systems, electric coffee makers, the extrusion of polymer sheets, etc.

On a holistic investigation of implicit/explicit/semi-implicit GS4-I framework and time step control for unsteady fluid dynamics

Purpose This paper aims to design and analyze implicit/explicit/semi-implicit schemes and a universal error estimator within the Generalized Single-step Single-Solve computational framework for First-order transient systems (GS4-I), which also fosters the adaptive time-stepping procedure to improve stability, accuracy and efficiency applied for fluid dynamics. Design/methodology/approach The newly proposed child-explicit and semi-implicit schemes emanate from the parent implicit GS4-I framework, providing numerous options with flexible and controllable numerical properties to the analyst. A universal error estimator is developed based on the consistent algorithmic variables and it works for all the developed methods. Applications are demonstrated by merging the developed algorithms into the iterated pressure-projection method for incompressible Navier–Stokes equations. Findings The child-explicit GS4-I has improved solution accuracy and stability properties, and the most stable option is the child explicit GS4-I(0,0)/second-order backward differentiation formula/Gear’s methods, which is new and novel. Numerical tests validate that the universal error estimator emanating from implicit designs works well for the newly proposed explicit/semi-implicit algorithms. The iterative pressure-correction projection algorithm is efficiently fostered by the error estimator-based adaptive time-stepping. Originality/value The implicit/explicit/semi-implicit methods within a unified computational framework are easy to implement and have flexible options in practical applications. In contrast to traditional error estimators, which work only on an algorithm-by-algorithm basis, the proposed error estimator is universal. They work for the entire class of implicit/explicit/semi-implicit linear multi-step methods that are second-order time accurate. Based on the accurately estimated local error, balance amongst stability, accuracy and efficiency can be well achieved in the dynamic simulation.

Effect of Inter Turbine Spacing in Omnidirectional Wind for Savonius Cluster: A Computational Fluid Dynamics and Artificial Neural Network Approach

Abstract This research explores the potential of wind energy as a sustainable solution to the environmental challenges by focusing on the deployment of vertical axis wind turbines in confined spaces, such as urban rooftops, ship decks and gas stations etc. It aims to identify the optimal configuration for a cluster of three rotors by varying geometric parameters, assessing the omnidirectionality of the rotors, and using an artificial neural network as an optimization tool. The methodology involves two-dimensional unsteady Reynolds-averaged Navier-Stokes computational fluid dynamics simulations followed by building and training an artificial neural network. The results indicate that the best cluster configuration, achieving a power coefficient of 0.2517, consists of a horizontal distance of 0.08D, vertical distance of 0.1D, and wind direction of 232°. The accuracy of neural network is demonstrated by a mere 1.206% discrepancy with the computational analysis, thus highlighting its potential as a time-saving tool in the optimization process. Additionally, the average power coefficient across all wind directions was found to be 0.194, thus confirming the strong omnidirectional characteristics of cluster. The study also notes a significant speed-up region between the rotors, which creates a low-pressure area, enhancing the power coefficient of the downstream rotor and demonstrating the advantages of this pressure-based turbine configuration. This comprehensive study establishes the efficacy of neural network in optimizing wind turbine clusters, thus significantly expediting their design and development process.

Effect of plaque micro-watershed changes on carotid atherosclerosis.

The study aims to elucidate the mechanisms underlying plaque growth by analyzing the variations in hemodynamic parameters within the plaque region of patients' carotid arteries before and after the development of atherosclerotic lesions. The study enrolls 25 patients with common carotid artery stenosis and 25 with tandem carotid artery stenosis. Based on pathological analysis, three-dimensional models of the actual blood vessels before and after the lesion are constructed for two patients within a two-year period. Computational fluid dynamics is employed to conduct unsteady periodic non-Newtonian fluid numerical simulations, enabling an in-depth investigation into the changes in the micro-environment of blood flow. During the systolic phase of the cardiac cycle, vortex regions are particularly prone to developing at the bifurcation point between the common carotid artery and the distal end of the internal carotid artery. In the early diastolic phase, blood reflux phenomena can be observed within the carotid artery. Towards the end of diastole, there is an expansion of vortex regions at the bifurcation point of the carotid artery. The shoulder region of initial small plaques within the blood vessel is susceptible to developing a low-speed recirculation zone, characterized by significantly reduced shear stress compared to the surrounding areas. Following vascular stenosis, the wall shear stress within the plaque domain generally increases; however, it maintains a consistent pattern of high central values and low upper shoulder values. The shear stress at the upper shoulder of the plaque of tandem carotid stenosis is below 0.4 Pa, whereas the central and lower shoulder regions exhibit shear stress exceeding 40 Pa. The dynamic parameters of the blood flow micro-environment exhibit variations throughout the cardiac cycle, and temporal disparities exist in local lesions within the carotid artery. Both common and tandem carotid artery stenosis are particularly prone to developing lesions at the shoulder of initial small plaques. The micro-flow characteristics within the plaque domain undergo alterations prior to and following the onset of carotid artery disease. Furthermore, the occurrence of restenosis and rupture is associated with the location of plaque growth.

Simulation of thermochemical effects on unsteady magneto hydrodynamics fluids flow in two dimensional nonlinear permeable media

This study aimed to simulate the thermochemical effects on unsteady magnetohydrodynamic (MHD) fluid flow in a two-dimensional nonlinear permeable medium under the influence of an external space-dependent magnetic field and a non-uniform heat source. Fluid flow is crucial in numerous natural and man-made systems, yet its complexities, especially in MHD contexts, are underexplored. The models momentum, energy, and concentration equations, accounting for the dependence of fluid and media properties, were transformed into nonlinear coupled ordinary differential equations using similarity transformations. These equations were solved numerically using the shooting technique, the sixth-order Runge-Kutta Fehlberg method, and Newton’s Raphson method, supported by Maple software. Computational results were generated for velocity, temperature, and concentration profiles. The skin-friction coefficient, Nusselt Number (which represents heat transfer rate), and Sherwood Number (indicating mass transfer) were also evaluated. The results indicated that velocity increased with the magnetic field parameter, permeability, thermal and mass Grashof Numbers, Prandtl Number, radiation, mass transfer parameters, and wall porosity. Conversely, velocity diminished with an increase in Schmidt Number, space and temperature-dependent heat generation parameters, and unsteadiness. The fluid temperature followed a similar trend, decreasing with increased magnetic field, permeability, Grashof numbers, and other parameters but showed a reverse effect when radiation and unsteadiness were high. Fluid concentration initially increased with smaller parameter values but declined with larger ones. The findings suggested that optimizing thermophysical parameters can significantly enhance heat and mass transfer in unsteady MHD flow through permeable surfaces, making the results relevant for biomedical applications.

Investigation of heat and mass transfer on unsteady MHD flow through a porous medium past an exponentially accelerated plate with stratification effects

AbstractThis research analyzes the effects of heat and mass transfer on unsteady magnetohydrodynamics fluid flow through a porous material along a vertical plate that accelerates exponentially and has both thermal and mass stratification. We find the solutions to the system's governing equations by employing the Laplace transformation approach and graphs are produced by implementing MATLAB software. The unique aspect of this problem is that we find the precise solution by applying the extremely effective Laplace transform approach, which yields an error‐free exact answer. The effect of flow variables on velocity, temperature, and concentration profiles are illustrated using graphs. The results show that when the magnetic field parameters are raised, there is a corresponding increase in temperature and decrease in velocity. As the permeability parameter increases velocity profile increases, temperature and concentration profiles decreases. The need to better understand fluid flow in a variety of engineering and environmental contexts—such as geothermal energy extraction, thermal management, chemical processing industries, and environmental control technologies—could be the driving force behind this study. Understanding flow mechanisms in both natural and artificially created porous environments is improved by this innovative method.

The velocity field to unsteady fluid flow in a circular cylinder with generalized Caputo fractional derivative

The velocity field to unsteady fluid flow in a circular cylinder with generalized Caputo fractional derivative

Heat and Mass Transfer in Unsteady MHD Casson Fluid Flow Over a Semi-Infinite Vertical Plate Through Porous Medium with Dissipative and Radiative Effects

Nowadays, Casson fluid and its diverse applications are highly effective across a vast array of industrial, biological and environmental sectors, due to its unique flow properties. This study focuses on the numerical investigation of the heat and mass transfer characteristics of an unsteady incompressible Casson fluid flow over a semi-infinite vertical flat plate by considering free convection effects. The fluid is conducting the electrical current as it moves through the porous medium. The formulation of the governing equation is based on the use of this phenomenon. In the model, the formulated governing equations are converted into non-dimensional form first, and the MHD mathematical model is analyzed using the boundary conditions. The scheme of finite difference method is implemented to solve the model, where concentration profiles are also discussed. Stability and convergence criteria are applied for the accuracy of numerical techniques, and the effects of various parameters on skin friction, rate of heat and mass transfer have been examined significantly. The results indicate that the temperature of the plate increases with the increase in the value of the magnetic parameter for the Casson fluid but the reverse is observed in its limiting case. The present results are compared and checked with previously published results and a remarkable conclusion is given at the end of the study.

Conditional neural field latent diffusion model for generating spatiotemporal turbulence

Eddy-resolving turbulence simulations are essential for understanding and controlling complex unsteady fluid dynamics, with significant implications for engineering and scientific applications. Traditional numerical methods, such as direct numerical simulations (DNS) and large eddy simulations (LES), provide high accuracy but face severe computational limitations, restricting their use in high-Reynolds number or real-time scenarios. Recent advances in deep learning-based surrogate models offer a promising alternative by providing efficient, data-driven approximations. However, these models often rely on deterministic frameworks, which struggle to capture the chaotic and stochastic nature of turbulence, especially under varying physical conditions and complex, irregular geometries. Here, we introduce the Conditional Neural Field Latent Diffusion (CoNFiLD) model, a generative learning framework for efficient high-fidelity stochastic generation of spatiotemporal turbulent flows in complex, three-dimensional domains. CoNFiLD synergistically integrates conditional neural field encoding with latent diffusion processes, enabling memory-efficient and robust generation of turbulence under diverse conditions. Leveraging Bayesian conditional sampling, CoNFiLD flexibly adapts to various turbulence generation scenarios without retraining. This capability supports applications such as zero-shot full-field flow reconstruction from sparse sensor data, super-resolution generation, and spatiotemporal data restoration. Extensive numerical experiments demonstrate CoNFiLD’s capability to accurately generate inhomogeneous, anisotropic turbulent flows within complex domains. These findings underscore CoNFiLD’s potential as a versatile, computationally efficient tool for real-time unsteady turbulence simulation, paving the way for advancements in digital twin technology for fluid dynamics. By enabling rapid, adaptive high-fidelity simulations, CoNFiLD can bridge the gap between physical and virtual systems, allowing real-time monitoring, predictive analysis, and optimization of complex fluid processes.

An efficient coupled fluid flow-geomechanics model for capturing the dynamic behavior of fracture systems in tight porous media

This paper introduces an efficient hybrid numerical discretization method designed to address the coupled mechanical challenges of geomechanics and fluid flow during pressure depletion in tight reservoirs. Utilizing the extended finite element method, this approach solves the elastic deformation of rock, while the mixed boundary element method precisely calculates the unsteady fluid exchange between the matrix and fractures. These numerical schemes are integrated fully, with temporal dynamics managed through a fully implicit method that effectively characterizes fracture deformation and fluid flow in hydrocarbon development. Furthermore, this model incorporates embedded pre-treatment to represent hydraulic macro-fractures and considers the effects of proppant. It captures dynamic information regarding the matrix and minor natural fractures through the double-porosity effective stress principle and a dual-medium implicit fracture characterization method. Thus, the proposed hybrid model provides a comprehensive depiction of the complex interplay between the matrix, natural fractures, and hydraulic fractures. The model's accuracy is validated through various examples, highlighting its reliability. This research offers valuable theoretical insights for advancing the development of unconventional hydrocarbon resources.

Performance assessment of Savonius wind turbine: Impact of the cylindrical deflectors with natural shapes

Savonius wind turbine, with various advantage features, is expanding its application for energy harvesting in urban and offshore environments. However, the drawback of this turbine relies on its relatively low aerodynamic efficiency. This study aims to enhance the Savonius wind turbine's aerodynamic performance to expand its effective application in urban areas and reduce offshore wind energy costs by using multiple cylindrical deflectors with natural geometry, changing from square to circular shapes. Results from the sequence of two-dimensional (2D) unsteady computational fluid dynamics (CFD) simulations show various performances gained depending on the deflector shapes. The highest power coefficient, with an increment of up to 133% over the turbine without the deflectors without the complex structure and the requirement of the rotated cylinder, is attained with the square cylindrical one at different wind conditions. The insight flow analysis reveals that the high jet flow formed between the turbine and the deflectors is the physical reason behind such improvement, through adding more positive pressure force on the advancing blade while increasing the recovery pressure on the concave side of the returning one. The results suppose the significance of the present study with a simple wind turbine-deflector configuration for high energy harvesting in urban and offshore environments with effective costs.

Impacts of Buoyancy and Joule Heating on Unsteady MHD Fluid Flow Along a Semi‐Infinite Vertical Porous Plate With Dufour, Chemical Reaction, and Radiation Effect

ABSTRACTAn analytical solution for unsteady, incompressible, laminar MHD fluid flow involving mass and heat transfer along a semi‐infinite vertical moving flat plate in a porous medium have been studied in this paper. Effects of heat radiation and absorption, Joule heating, Dufour, thermal and solutal buoyancy, and first order chemical reaction of are discussed under suitable physical conditions. It is postulated that the plate will migrate in the fluid's motion's direction due to the presence of a uniform magnetic field normal to the porous surface. The regular perturbation technique is used to solve the dimensionless governing equations. The mathematical derivations for fluid velocity, temperature, and concentration are evaluated; apart from that, skin friction, rate of mass and heat transfer at the plate are also expressed. The present outcomes are compared with previously obtained results and are found to be in excellent agreement. It is observed that the fluid velocity and temperature enhanced with thermal and solutal buoyancy forces as well as the Dufour effect. Also, with an increase in chemical reaction parameter, there is a decrease in fluid velocity, temperature, and concentration. Skin friction and Nusselt number increase with higher heat absorption parameter values. Schmidt number and chemical reaction parameter both lead to a rise in Sherwood number. Applications for these models have been observed in a number of industrial and technical methods.

Exploring concentration-dependent transport properties on an unsteady Riga plate by incorporating thermal radiation with activation energy and gyrotactic microorganisms

Abstract The aim of this study is to examine the entropy generation (EG) associated with the transfer of mass and heat in a concentration-dependent fluid with thermal radiation and activation energy, specifically in the context of an unsteady Riga Plate with gyrotactic microorganism. It is important to solve the ordinary differential equations generated from the controlling partial differential equations using Lie symmetry scaling to verify their quality and reliability. The system’s anticipated physical behavior is compared to Mathematica’s Runge–Kutta–Fehlberg numerical solution. Source parameters are essential for validation since they offer accurate results. Methodically change these values as a percentage to determine how they affect the unsteady fluid’s density, mass, and heat transfer over the Riga plate. Velocity, temperature, nanoparticle concentration and microorganism concentration profiles decrease with varying values of the unsteadiness parameter. EG increases with increasing values of concentration difference, thermal radiation, and Reynold number parameters. The Nusselt number experiences a 26.11% rise as a result of radiation when the unsteadiness parameter is A = − 0.25 A=-0.25 , in comparison with the scenario without radiation. Mass transfer upsurges with increasing values of the Brownian motion parameter and reduces with increasing values of thermophoresis parameter. To verify our conclusions, we compare calculated data, specifically the skin friction factor, to theoretical predictions. Tabular and graphical data can show how physical limits affect flow characteristics.

Mitigation of vibrations caused by inter-blade vortices using pumping cap for natural aeration

Abstract In 2014, Andritz received a contract to refurbish six Francis turbines with a total capacity of 840 MW. During the commissioning of the first unit, unexpected vibrations occurred within a power range of 25 to 65 MW, and Andritz was requested to find a solution. Unsteady computational fluid dynamics CFD simulations, revealed that the vibrations originated from intermittently cavitating inter-blade vortices. Conventional solutions involving compressed air injection were rejected, leaving natural aeration as the only viable option. Andritz explored various options for natural aeration by CFD and later, by means of homologous model tests. The solution was able to accommodate suction heads of approximately 10 meters and consisted of a specialized runner cap, referred to as pumping cap, which allowed for natural aeration through the hollow turbine shaft. The cap was optimized using two-phase CFD, and once installed on the prototype, it demonstrated a reduction of aproximately 50% in the peak level of vibration and noise. This achievement fully satisfied the customer, leading to the acceptance of the machine.

The development of undercut and bulge on a solidified surface

Abstract This study numerically investigates the development of undercuts and bulges parallel to the scanning direction on the surface solidified from a thermocapillary molten pool. The analysis considers various parameters, including power-off time, active solute concentration, beam power and radius, surface tension, liquid thermal conductivity, viscosity, and density. The formation and shapes of undercuts and bulges directly impact the yield, fatigue, fracture strength, and stress concentration in the solidified region. Unsteady two-dimensional fluid flow and heat transfer, which drive surface deformation in metals containing surface-active solutes (e.g., iron with sulfur), are solved using COMSOL Multiphase version 5.6. The development of the undercut, bulge, and molten pool is identified in six stages, based on whether the peak temperature is below the melting temperature, between the melting and critical temperatures, or above the critical temperature during heating and power-off periods. The critical temperature, determined as a function of solute content and temperature, leads to inward surface flow in the undercut near the pool edge, while the bulge in the central region can form due to either inward or outward surface flow. The predicted undercut depth and bulge height align well with previous scaling analyses and experimental data from laser polishing. These findings are relevant to various processes, including welding, additive manufacturing, polishing, melting, and solidification.

A Review of Numerical Methodologies for Predicting Rotating Stall and Surge in High-Speed Centrifugal Compressors

Abstract High-speed supersonic radial compressors are a critical enabling technology for meeting the requirements of future aviation-propulsion and thermal-management systems. These turbomachines must be designed to be both efficient and robust on the widest possible operating range. Flow instabilities in the form of rotating stall and surge are therefore phenomena that must be accurately predicted early in the design process. Unsteady full-annulus computational fluid dynamics (CFD) can be used to get accurate information about the onset of instabilities, but at the expense of costly simulations. As a result, the design of new compressors continues to rely on existing correlations for the prediction of the critical mass flowrate. This approach, however, leads to suboptimal compressor designs. This article provides a review of the numerical methodologies that can be used for the accurate prediction of the critical mass flowrate in high-speed centrifugal compressors. Methods of different fidelity level and computational cost are described. Two particularly promising models, namely, those proposed by Spakovszky and Sun, are subsequently examined in more detail. Exemplary applications of these two models are finally discussed.

AN AERODYNAMIC INVESTIGATION OF A HIGH-PRESSURE TURBINE USING ROTOR CASING STATIC PRESSURE MEASUREMENTS AT ENGINE REPRESENTATIVE CONDITIONS WITH DIFFERENT TIP DESIGNS, TIP GAPS AND INLET TEMPERATURE PROFILES

Abstract A rotating High-Pressure (HP) turbine, in modern aircraft engines, is subjected to high cyclic thermal and mechanical loads. Shroudless turbines experience high heat loads on the rotor tip and casing, which makes them one of the life-limiting components for an engine. If the rotor tip starts to erode, then the tip clearance increases which increases the over-tip leakage flow, resulting in reduced stage efficiency and ultimately, the engine lifetime. The Oxford Turbine Research Facility (OTRF) is a high- speed rotating transient test facility that allows unsteady aerodynamics and heat transfer measurements, at engine representative conditions. This paper presents an experimental investigation, of the HP turbine rotor casing aerodynamics, performed in the OTRF. Steady and unsteady casing static pressure measurements were acquired, using pneumatic lines and high-frequency response (∼ 100 kHz) Kulite pressure transducers respectively. The single-stage HP turbine consisted of cooled vanes (featuring film and trailing edge slot cooling), and uncooled rotor blades. Three different tip designs (two squealers and one flat) were tested, at two tip gaps, and with two inlet temperature profiles that included a spatially uniform total temperature profile and an engine representative HP turbine inlet total temperature profile. In parallel, a numerical investigation of the experimental test cases is presented using unsteady Computational Fluid Dynamics (CFD) predictions. The experimental results from this study provide a unique dataset to validate numerical models.

Numerical Analysis and Experimental Validation of Trimaran and Pentamaran Resistance at Various Separation Distances

Trimaran and pentamaran are multihull types with an odd number of hulls, namely three and five hulls, generally consisting of one center hull and two or four side hulls smaller than the center hull, which can reduce ship resistance. The trimaran and pentamaran have a more complex phenomenon than the monohull, because of the interaction between the main hull and the side hull, which causes interference caused by changes in flow velocity, pressure changes, and wave interactions generated by each hull. The objective of this study is to analyze the resistance of trimaran and pentamaran NPL-4b models with transom-symmetrical hull and separation distances, specifically S/L ratios of 0.2, 0.3, and 0.4. Since a more limited base of experience exists for multihull ships, experimental or numerical modeling techniques are essential for designers. Numeric investigations were conducted using Numeca software, and experiments were performed in a towing tank. Both methods follow ITTC procedures. Furthermore, the numerical analysis with CFD simulation modifies the Navier-Stokes equation using the turbulence model k-ꞷ SST to generate the RANS equation so that unsteady fluid flow problems can be calculated. It can be implemented in predicting resistance in Froude numbers (Fr) 0.2 to 0.6 at the systematic series of trimaran and pentamaran hull shapes at the model scale. The simulation results were compared to experimental data to validate the resistance of the ships. Overall, good resistance was produced by the trimaran and pentamaran in the C configuration at an S/L ratio of 0.4 with a total resistance coefficient CT of 6.60 x 10-3 and 7.37 x 10-3, respectively. The two results are in good agreement, both methods have a discrepancy of 3.70 %. Fluctuations influence the resistance in the wetted surface area (WSA), wave interactions between hulls, ship velocity, and wave propagation in the aft hull.