Zhiyin Yang

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• Professor of Aerospace Engineering
• Professor (Full) at University of Derby

Large-eddy simulation (LES) was originally proposed for simulating atmospheric flows in the 1960s and has become one of the most promising and successful methodology for simulating turbulent flows with the improvement of computing power. It is now feasible to simulate complex engineering flows using LES. However, apart from the computing power, sig...

Numerical studies of laminar-to-turbulent transition in a separation bubble subjected to two free-stream turbulence levels (FST) have been performed using Large-Eddy Simulation (LES). Separation of the laminar boundary layer occurs at a curvature change over a plate with a semi-circular leading edge at Re = 3450 based on the plate thickness and the...

A large-eddy simulation has been performed of a flat-plate boundary layer undergoing transition to turbulence under free-stream turbulence at a level of 6%. The properties of the simulated transition match those found experimentally: not only is the position and length of transition in agreement with available data, but the mechanism of tran...

Transition arising from a separated region of flow is quite common and plays an important role in engineering. It is difficult to predict using conventional models and the transition mechanism is still not fully understood. We report the results of a numerical simulation to study the physics of separated boundary-layer transition induced by a c...

It has been well established that large-scale structures, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of those large-scale structures vary from flow to flow such as counter-rotating vortices in wake flows, streaks and hairpin vortices in turbulent boundary layer. There has bee...

Diesel trains play a vital role in the UK’s rail passenger transport. Despite efforts to expand electrification, over 10% of the UK’s rail routes will remain non-electrified. To reduce emissions and phase out diesel trains by 2040, the UK rail network is actively exploring alternative fuels. This paper presents a comprehensive technical, economic,...

Integrating Artificial Intelligence with CFD to Optimise the Combustion Process

This paper presents a comprehensive investigation into the collision dynamics of equal and unequal-sized nanodroplets on a flat surface using molecular dynamics simulations, revealing new insights into scaling laws and energy dissipation mechanisms. The simulations, conducted with the Large-Scale Atomic/Molecular Massively Parallel Simulator softwa...

The impact of droplets on solid surfaces is a crucial fluid phenomenon in the additive industry, biotechnology, and chemistry, where controlling impact dynamics and duration is essential. While extensive research has focused on flat substrates, our understanding of impact dynamics on curved surfaces remains limited. This study seeks to establish ph...

Three-dimensional (3D) computational fluid dynamics (CFD) simulations have been carried out to investigate the complex interaction of a planar shock wave (Ma = 1.22) with a cylindrical bubble. The unsteady Reynolds-averaged Navier–Stokes (URANS) approach with a level set coupled with volume of fluid (LSVOF) method has been applied in the present st...

This research focuses on understanding the behavior of diesel fuel droplets during combustion in engines to optimize engine performance and minimize emissions. Multi-scale modeling techniques, such as molecular dynamics and kinetic theory, are used to simulate the fluid dynamics within fuel droplets and gain insights into heat transfer and chemical...

In any healthcare setting, it is important to monitor and control airflow and ventilation with a thermostat. Computational fluid dynamics (CFD) simulations can be carried out to investigate the airflow and heat transfer taking place inside a neonatal intensive care unit (NICU). In this present study, the NICU is modeled based on the realistic dimen...

Influences of non-uniform incoming flow on the wind turbines blades forces and root bending moments (RBMs) are not fully understood. To advance our current understanding, numerical studies of a three-bladed horizontal axis wind turbine with cylinders placed in front of it to produce non-uniform flow approaching the turbine with different non-unifor...

Effects of yawed wind turbines on the wake structure are not fully understood. To obtain a better understanding, numerical studies of a small-scale three-bladed horizontal axis wind turbine at TSR=6.7 with yaw angles of zero, 15, 30 and 45 degrees have been carried out to investigate the wake characteristics of the turbine in the near- and far-wake...

The aerodynamic efficiency of trucks is very low because of their non-streamlined box shape, which is subject to practical constraints, leaving little room for improvement in terms of aerodynamic efficiency. Hence, other means of improving the aerodynamic efficiency of trucks are needed, and one practical yet relatively simple method to reduce aero...

The interaction of horizontal axis wind turbines (HAWTs) and large-scale energetic flows is not fully understood. The unsteady flow approaching turbines could result in highly unsteady blade forces and root bending moments (RBMs) which would have a strong influence on the turbine operational life span, especially for large scale wind turbines. To p...

Two-dimensional and three-dimensional computational fluid dynamics studies of a spherical bubble impacted by a supersonic shock wave (Mach 1.25) have been performed to fully understand the complex process involved in shock–bubble interaction (SBI). The unsteady Reynolds-averaged Navier–Stokes computational approach with a coupled level set and volu...

Effects of yawed approaching flows on the wake structure of axial-flow tidal turbines are not fully understood. To obtain a better understanding, numerical studies of a laboratory-scale three-bladed horizontal axis tidal turbine at tip speed ratio TSR=5.2 with yaw angles of zero and 15 • have been carried out to investigate the wake characteristics...

Our current understanding on the dynamic interaction between large-scale motions in the approaching turbulent flow and wind turbine power is very limited. To address this, numerical studies of a small-scale three-bladed horizontal axis wind turbine with cylinders placed in front of it to produce energetic coherent structures of varying scale relati...

Effects of yawed incoming flow on wind turbine blades forces and root bending moments (RBMs) are not fully understood. To advance our current understanding, numerical studies of a small-scale three-bladed horizontal axis wind turbine at TSR = 6.7 with yaw angles of zero and 45° have been carried out to examine the variations of blade and rotor load...

Numerical simulations have been carried out to advance our current understanding of flow around two dimensional (2D) and three dimensional (3D) square shaped tandem bluff bodies at a Reynolds number of 22,000, especially to shed light on the sudden change of the downstream body's drag coefficient. The Reynolds-Averaged Navier-Stokes (RANS) approach...

Aerodynamic drag reduction of tractor-trailer combination trucks is critically important to improve their fuel consumption which consequently results in lower emissions. One practical method to reduce aerodynamic drag of a truck is by mounting drag reduction devices on the truck. This paper presents a numerical study of turbulent flow over a simpli...

Reducing aerodynamic drag of heavy trucks is crucially important for the reduction of fuel consumption and hence results in less air pollution. One way to reduce the aerodynamic drag is the deployment of drag reduction devices at the rear of trucks and this paper describes a numerical study of flow over a bluff body with rear drag devices using the...

Numerical simulations have been carried out to advance our current understanding of flow around two dimensional (2D) and three dimensional (3D) square shaped tandem bluff bodies at a Reynolds number of 22,000, especially to shed light on the sudden change of the downstream body's drag coefficient. The Reynolds-Averaged Navier-Stokes (RANS) approach...

Turbulent flow past a circular cylinder at super-critical Reynolds numbers is simulated using large eddy simulation in this study. A novel combination of O-and H-grid structures is used to reduce mesh cells and, in turn, the computational cost. To investigate the influence of sub-grid scale (SGS) models on the accuracy of simulations, four differen...

Little is known about how the range of scales in the approaching turbulent flow can interact dynamically with wind turbines and influence its ability to produce power. Here, a numerical study of a horizontal-axis wind turbine at different Reynolds numbers (corresponding to different tip speed ratios) has been conducted to investigate the instantane...

The evolution of turbulence characteristics downstream of a laboratory-scale three-bladed horizontal axis turbine is investigated in this study. Large eddy simulation (LES) coupled with the Actuator Line Modelling (ALM) is used to simulate the flow. The numerical results compare well against experimental data, which shows that the LES/ALM technique...

Heavy trucks are aerodynamically inefficient due to their un-streamlined body shapes, leading to more than of 60% engine power being required to overcome the aerodynamics drag at 60 m/hr. There are many aerodynamics drag reduction devices developed and this paper presents a study on a drag reduction device called Cross Vortex Trap Device (CVTD) dep...

Large-eddy simulation (LES) has been carried out to investigate the transition process of a separated boundary layer on a flat plate. A streamwise pressure distribution is imposed to mimic the suction surface of a low-pressure turbine blade, and the free-stream turbulence intensity at the plate leading edge is 2.9%. A dynamic subgrid scale model is...

Transition from laminar flow to turbulent flow is of great practical interest as it occurs in many engineering flows and often plays a critical role in aerodynamics and heat transfer performance of those flow devices. There could be many routes through transition, depending on flow configuration, geometry and the way in which transition is initiate...

It is well established in the natural transition of an attached boundary layer that the transition process starts with a two–dimensional primary instability (Tollmien–Schlichting wave, denoted as TS wave), followed by usually a three-dimensional secondary instability (fundamental mode or subharmonic mode) leading to the breakdown to turbulence. How...

The process through which a laminar flow undergoes transition to turbulence is of great fundamental and practical interest. Such a process is hugely complex as there are many diverse routes for a laminar flow to become turbulent flow. The transition process is usually initiated by flow instabilities-a primary instability stage followed by a seconda...

The accuracy of computational fluid dynamic (CFD)-based heat transfer predictions have been examined of relevance to liquid cooling of IC engines at high engine loads where some nucleate boiling occurs. Predictions based on (i) the Reynolds Averaged Navier-Stokes (RANS) solution and (ii) large eddy simulation (LES) have been generated. The purpose...

A numerical study of flow over a bluff body with drag devices has been carried out using the Reynolds-Averaged-Navier-Stokes (RANS) approach and the per-formance of three turbulence models, the realizable k-, the SST k- and a Reynolds Stress Model (RSM), has been assessed. The predictions of both the mean and turbulent quantities agree reasonably...

Traditionally the so called Reynolds-Averaged Navier-Stokes (RANS) and Unsteady RANS (URANS) have been the main numerical tools for computing gas turbine flows due to their computational efficiency and reasonable accuracy. However, the limitations of RANS and URANS to resolve appropriate details and capture some essential flow features associated w...

A novel approach is proposed for precise control of two-phase spray evaporative cooling for thermal management of road vehicle internal combustion (IC) engines. A reducedorder plant model is first constructed by combining published spray evaporative cooling correlations with approximate governing heat transfer equations appropriate for IC engine th...

A numerical study is described to predict, in the non-boiling regime, the heat transfer from a circular flat surface cooled by a full-cone spray of water at atmospheric pressure. Simulations based on coupled computational fluid dynamics and conjugate heat transfer are used to predict the detailed features of the fluid flow and heat transfer for thr...

Laminar-to-turbulent transition is of great practical interest as it occurs in many engineering flows and often plays a critical role in aerodynamics and heat transfer performance of those flow devices. There could be many routes through transition, depending on flow configuration, geometry and the way in which transition is initiated by a wide ran...

When two bluff bodies is in close tandem, i.e, the distance between blocks D is less than half of the height of the body H, the flow field is very similar to that in the gap between tractor and trailer in a truck, and hence understanding such a flow field would help to reduce the gap drag of a truck. This paper presents a numerical study of the flo...

Evaporative cooling (EC) is a potentially attractive method of thermal management in highly downsized engines. As a benchmark for robust EC system development, a novel half-unit-cylinder-head has been designed to study the heat transfer achievable with evaporative cooling strategies under realistic hot metal conditions with an appropriate coolant f...

Typical PEM fuel cell models usually involve more than 106 mesh elements making the computation very intense. This necessitates an effective way to mesh the computational domain with a minimum number of mesh points while, at the same time, maintaining good accuracy. The meshing strategy in each flow direction is investigated systematically in the c...

The evaporative cooling system concepts proposed over the past century for engine thermal management in automotive applications are examined and critically reviewed. The purposes of this review are to establish the evident system shortcomings and to identify the remaining research questions that need to be addressed to enable this important technol...

Large-eddy simulation (LES) is conducted to study the transition process of a separated boundary layer on a flat plate with an elliptical leading edge. A streamwise pressure distribution is imposed and the free stream turbulence intensity is 3% to mimic the suction surface of a low-pressure turbine (LPT) blade. A dynamic sub-grid scale model is emp...

Computational fluid dynamics (CFD) is a major tool in PEM fuel cell research. Typical three-dimensional PEM fuel cell models involve more than 106 mesh elements. This makes the computation very intense and necessitates a methodology to mesh the computational domain that can keep the number of elements to a minimum while maintaining good accuracy. I...

Typical PEM fuel cell models usually involve more than 106 mesh elements making the computation very intense. This necessitates an effective way to mesh the computational domain with a minimum number of mesh points while, at the same time, maintaining good accuracy. The meshing strategy in each flow direction is investigated systematically in the c...

A three-dimensional, multispecies, multiphase polymer electrolyte (PEM) fuel cell model was developed in order to investigate the effect of the flow-field geometry on the steady-state and transient performances of the cell under an automotive operation. The two most commonly used designs, parallel and single-serpentine flow fields, were selected as...

Combustion process of conventional liquid fuels and biofuels depend on many factors including thermo-physicochemical properties associated with such fuels, their chemical structure and the combustion infrastructure used. This manuscript summarises the computational results of a steady CFD simulation for reactive flows performed to validate advanced...

An isothermal and non-isothermal numerical study of effusion cooling flow and heat transfer is conducted using a Reynolds-averaged Navier–Stokes (RANS) approach. A Reynolds stress transport (RST) turbulence model is used to predict the flow field of a staggered array of 12 rows of effusion holes, each hole inclined at 30° to the flat plate. The Rey...

A complex flow field is created when a vertical/short take-off and landing aircraft is operating near ground. One major concern for this kind of aircraft in ground effect is the possibility of ingestion of hot gases from the jet engine exhausts back into the engine, known as hot gas ingestion, which can increase the intake air temperature and also...

Numerical studies based on steady Computational Fluid Dynamics (CFD) for reactive flows were performed with the objective of validating advanced reaction mechanisms used to study spray combustion for both conventional and Biofuels. The SST-4 equation model was used to model turbulence, while more than one (comprehensive) reaction mechanisms were us...

A large-eddy simulation (LES) of a transitional separated flow over a plate with a semi-circular leading at low (<0.2%) and high (5.6%) free-stream turbulence (FST) has been performed, using a co-located grid with the Rhie-Chow pressure smoothing. A numerical trip is used to produce a high FST level and a dynamic subgrid-scale model is also employe...

Numerical studies have been carried out on a battle damaged NACA 641-412 half wing of aspect ratio 8.2 at a Reynolds number of 5.5 x 105. The simulated gunfire damage was represented by a single hole with a diameter of 0.2 wing chord. The hole was centred at half chord and at spanwise locations of 450mm and 650mm from wing root. Computational Fluid...

A very complicated three-dimensional (3D) flow field is generated beneath a Vertical/Short Take-Off and Landing (VSTOL) aircraft when it is operated near the ground. This flow field can be represented by the configuration of twin impinging jets along the spanwise direction in a cross-flow. This paper describes a Computational Fluid Dynamics (CFD) s...

Transition from laminar flow to turbulent flow occurs very often and plays a crucial role in many practical engineering flows. There are many different kinds of transition and broadly speaking they can be classified into three categories: Classical transition in attached boundary; bypass transition in attached boundary layer and separated boundary...

Lean premixed combustion systems, attractive for low NOx performance are, however, susceptible to thermo-acoustic instabilities - the interaction between the unsteady heat release of combustion and acoustic waves. In the present work, a hybrid, coupled CFD approach is described, which aims to combine the computational efficiency of incompressible L...

Transition from laminar to turbulence in separated-reattached flow occurs frequently and plays a very important role in engineering. Hence, accurately predicting transition is crucial since the transition location has a significant impact on aerodynamics performance and a thorough understanding of the transition process can greatly help to control...

Laminar-to-turbulent transition in shear layer of separated flows is of practical importance. A thorough understanding of transition process is crucial for its prediction and control; to delay the turbulent phase where laminar flow characteristics are desirable or to accelerate it where high mixing and heat transfer rates of turbulent flow are of i...

This paper describes the Large-Eddy Simulation (LES) of a droplet laden mixing layer. The method uses an Eulerian description of the carrier flow with a Lagrangian formulation for the dispersed phase. Special treatment of inlet conditions for both phases is critical. Sub-grid scale dispersion effects are investigated, predictions of Sauter Mean Dia...

The transitional separated–reattached flow on a flat plate with a blunt leading edge under 2% free-stream turbulence (FST) is numerically simulated using the Large-eddy simulation (LES) approach. The Reynolds number based on the free-stream velocity and the plate thickness is 6500. A dynamic subgrid-scale model is employed and the LES results compa...

This article is closed access. It was published in the Journal of Aircraft [© American Institute of Aeronautics and Astronautics] and is available from: http://dx.doi.org/10.2514/1.39839 Wind-tunnel tests have been carried out on a battle-damaged NACA 641–412 half-wing aspect ratio of 8.2. The simulated gunfire damage had a diameter of 0.2 wing cho...

An isothermal numerical study of effusion cooling flow is conducted using a large eddy simulation (LES) approach. Two main types of cooling are considered, namely tangential film cooling and oblique patch effusion cooling. To represent tangential film cooling, a simplified model of a plane turbulent wall jet along a flat plate in quiescent surround...

Large-eddy simulation (LES) of transitional separating-reattaching flow on a two-dimensional square surface mounted obstacle and a forward facing step has been performed using a dynamic sub-grid scale model. The Reynolds number based on the uniform inlet velocity and the obstacle/step height is 4.5 × 10. The mean LES results for both the obstacle a...

Large Eddy Simulation (LES) has been employed to simulate a separated boundary layer transition with 2% free stream turbulence level and without free stream turbulence on a flat plate with a blunt leading edge. The entire transition process leading to breakdown to turbulence has been shown by flow visualization and large-scale coherent structures h...

A new one-equation subgrid scale (SGS) model that makes use of the transport. equation for the SGS kinetic energy (k(SGS)) to calculate a representative velocity scale for the SGS fluid motion is proposed. In the k(SGS) transport equation used, a novel approach is developed for the calculation of the rate of dissipation of the SGS kinetic energy (6...

It is well known that large-scale organised motions, usually called coherent structures, exist in many transitional and turbulent flows. The topology and range of scales of coherent structures change widely in different flows. However, it is not well established what kind of large-scale coherent structures exists in separated/reattached transitiona...

The present paper describes an LES prediction of turbulent diffusion flame combustion in a simplified axi-symmetric combustor geometry. The calculations are carried out using a well-tested finite volume incompressible LES code which has been modified to handle variable density and reacting flows. The basic mixture fraction conserved scalar method i...

A novel implementation of a digital filter based inlet condition generator for Large Eddy Simulation (LES) is presented. The effect of using spatially varying turbulence scales as inputs is investigated; it is found that this has impact on both accuracy and affordability, and has prompted the algorithm implementation changes described in the paper....

Rising buoyant plumes from a point heat source in a naturally ventilated enclosure have been investigated using large-eddy simulation (LES). The aim of the work is to assess the performance and the accuracy of LES for modelling buoyancy-driven displacement ventilation of an enclosure and to shed more light on the transitional behaviour of the plume...

Large-eddy simulation (LES) of transitional separating–reattaching flow on a square surface mounted obstacle has been performed. The Reynolds number based on the uniform inlet velocity and the obstacle height is 4.5 × 103. A dynamic subgrid-scale model is employed in this work. The mean LES results compare favourably with the available experimental...

Methods for the direct and large-eddy simulation of flows about turbomachinery blading are presented. For incompressible flows, both direct and large-eddy simulation require the solution of a Poisson equation for pressure, which is frequently the main source of computational expense in simulations within complex boundaries. Marked computational adv...

The highly turbulent flow occurring inside gas-turbine combustors requires accurate simulation of scalar mixing if CFD methods are to be used with confidence in design. This has motivated the present paper, which describes the implementation of a passive scalar transport equation into an LES code, including assessment/testing of alternative discret...

An impinging jet in a crossflow is a flow case representative of a jet-lift aircraft operating in ground effect. Accurate modelling of this flow field is essential in predicting the practical flow problems associated with these aircraft; in particular the ingestion of hot gas into the engine intakes, and the importance of the ground vortex contribu...

The effect of inputting either uniform or spatially varying turbulence scales into an inlet condition generator for LES prediction has been investigated. LES calculations of a channel flow with a periodically repeating constriction were used as a benchmark test case. Simulations using a streamwise periodic boundary condition (PBC) were first compar...

The chapter describes the implementation of a passive scalar transport equation into an existing large eddy simulation (LES) code, including assessment/testing of alternative discretization schemes to avoid over/undershoots and to prevent excessive smoothing. The numerical schemes are evaluated using a simple test case involving pure scalar convect...

Large-eddy simulation (LES) of transitional separating-reattaching flow on a flat plate with a blunt leading edge has been performed. The Reynolds number based on the uniform inlet velocity and the plate thickness is 6.5 x 10(3). A dynamic subgrid-scale model is employed in the transitional flow case. The LES results compare reasonably well with th...

The present paper describes a study that is aimed at establishing and quantifying the benefits of the Large Eddy Simulation (LES) method for predicting scalar turbulent transport in a combustor relevant jet-mixing problem. A non-reacting co-annular jet mixing configuration is considered for which comprehensive experimental data for both velocity an...