Papers by hossein hamdani
A Machine Learning Based Approach to Identify Drones Using Cfd Simulated Acoustic Data
Social Science Research Network, 2023
Fluid Dynamics, 2020
Ongoing development concerning to increase engine thrust to weight ratio in a gas turbine engine ... more Ongoing development concerning to increase engine thrust to weight ratio in a gas turbine engine which gives rises to extremely loaded compressor stages. Highly loaded compressors stability is associated with low energy tip leakage flow (TLF) which leads to the flow blockage and thermodynamic losses. This causes greater adverse effects in transonic axial flow compressors owing to the interaction of shock wave and tip leakage flow. The current paper aims for a detail investigation of tip clearances flow field region and their profound effects on aerodynamic performance, stability range and stability margin of low aspect modern transonic axial flow compressor through mathematical modeling and numerical simulation using ANSYS CFX software. Detail rotor flow field was numerically and computationally investigated at zero tip clearance, above and below of design tip clearance to conclude the performance of compressor at suitable tip clearance. A mathematical model has been established to predict the behavior of compressor rotor at choking, peak efficiency and near stall point mass flow rate conditions at different tip clearances. Mathematical model is developed to predict the behavior of compressor at different tip clearances. Furthermore, mathematical-based model results are validated with the computational results. The eminence of both model prediction and the numerical solution was assessed, and conclusions were drawn.
Effect on Dynamic Stall on Cambered Airfoil with Drooping Leading Edge Control
44th AIAA Aerospace Sciences Meeting and Exhibit, Jan 9, 2006
Effect of Reynolds number on leading edge vortex for a wing in unsteady motion
The present study focuses on investigating the persistence of delayed stall for Micro Air Vehicle... more The present study focuses on investigating the persistence of delayed stall for Micro Air Vehicles at Re-34,000. The motivation behind present research is to find out the effect of Reynolds number on aerodynamic force production and formation of leading edge vortex on a wing in unsteady motion. Computations are done on a corrugated wing in sweeping motion and pure translation at Reynolds number 3500 and 34,000. For sweeping motion, at 10 degree angle of attack, flow remain attached to the wing with no signs of leading edge vortex and the force coefficients at Re 34000 were higher than Re 3500 throughout the sweeping motion. For sweeping motion, at angle of attack of 40°, delayed stall continued to manifest itself at Re 34000. At Re 34000, the size of leading edge vortex was comparatively small but the strength of leading edge vortex core was relatively more and signs of vortex break down were eminent at 90 percent of wingspan. However, at Re 3500, signs of vortex break down were observed at 70 percent of wingspan. In pure translation, “stall absent” mechanism was not seen at any Re, as leading edge vortex was formed and it then shed into the wake. In short, it can be concluded that delayed stall continues to act as lift enhancement mechanism for MAV but flow structure and span wise vortex break down pattern changes with the change in Reynolds number.
Flow Angularity and Swirl Flow Analysis on Transonic Compressor Rotor by 1-Dimensional Dynamic Turbine Engine Compressor Code and CFD Analysis
Fluid Dynamics, Mar 1, 2021
Abstract— The performance and stability of a low-bypass turbofan transonic axial compressor with ... more Abstract— The performance and stability of a low-bypass turbofan transonic axial compressor with a nonuniform inlet flow is a significant concern in recent times. In both military and commercial aircraft, serpentine ducts produce significant inlet swirl distortion. Moreover, the nonuniform inlet flow frequently acts upon aircraft gas-turbine engines causing deteriorating effects on the aircraft engine. High circumferential swirl flows and inlet flow angularity decrease the aerodynamic performance and the stall margin and increase the rotor blade loading. The current paper is aimed at the investigation of the flow field in the tip clearance region of low-bypass turbofan transonic compressor rotor under nonuniform circumferential flow conditions through numerical simulation using Ansys CFX. The mathematical models based on 1D Mean Line Code and Dynamic Turbine Engine Compressor Code (DYNTECC) are used to analyze the nonuniform inlet swirl flow of the compressor rotor. The mathematical model is limited to compute the multistage compressor characteristics for the compression system and the combustor of a turbine engine. For the single-stage swirl flow analysis current paper focuses on the CFD based results. The results based on CFD show that co-swirl patterns slightly improve the stability range of the compressor; counter-swirl flows diminish it.
Journal of Applied Fluid Mechanics, 2018
The effect of various conditions on the thrust generation of 2-D airfoil in pure plunging motion ... more The effect of various conditions on the thrust generation of 2-D airfoil in pure plunging motion has been investigated. These conditions include different airfoil shapes, different Reynolds numbers (Re) and reduced frequencies (K). The three different shapes used in this study are the NACA0014, the ellipse, and the flat plate airfoil, whereas, the three Re used in the study are 1000, 10000, and 25000 for the three values of K at 2.0, 1.0, and 0.5. For all these parametric studies, the thickness (t/c ratio) of all the airfoil has been kept as constant at 14% t/c ratio. During sinusoidal plunging motion, CL and CD varies in a sinusoidal manner however CL and CD lags with the airfoil motion and the time averaged lift coefficient over one complete cycle is zero whereas the time averaged drag coefficient is negative and non-zero i.e. thrust is produced. The reason behind the thrust generation is due to the formation of the Reverse Karman Vortex Street in the wake of the airfoil.NACA0014 airfoil produces more negative values of the drag coefficient as compared to the ellipse and flat plate which indicates that the shape effect is important for thrust generation which is due to the pressure changes that occur close to the leading edge of the airfoil and it is more pronounced for an airfoil with large Δy variation near the leading edge , for instance NACA 0014. As the Re is increased, the time averaged drag coefficient becomes more negative and the thrust produced by the NACA0014 airfoil remains higher as compared to the other two airfoil which shows that the airfoil shape effect is dominant. As K reduces, time averaged drag coefficient (thrust) decreases and the airfoil shape effect becomes less prominent as K is decreased (or the unsteady effect decreases). It is seen that for all the cases, the CDv (drag due to viscous forces) is very small and major contribution of negative drag (thrust) comes from the pressure forces.
Journal of Applied Fluid Mechanics, 2017
The aerodynamic force and the flow structure of a wing performing hovering motion at small Reynol... more The aerodynamic force and the flow structure of a wing performing hovering motion at small Reynolds number (Re=4000) is calculated by computationally solving the 3D Navier-Stokes equations. The computations are performed for the hovering motion which consists of stroke 1, followed by the flipping motion for reversing the direction and then the stroke 2 (similar to stroke 1 but in the opposite direction). The intent of the study is to research the effects of different scheduling of the flip motion between the two strokes. At Re=4000, the delayed stall mechanism is noted during the azimuth rotation of a wing with a high value of CL due to stabilized Leading Edge Vortex. The lift contribution during the flip (pitch rotation for reversing the direction) for the complete stroke is not substantial. During a stroke, the wing encountered the wake from the previous stroke in which, the wake does not contribute positively.
Journal of Applied Fluid Mechanics, 2017
An Unsteady force generation mechanisms (delayed stall, wake capture and rotational lift) during ... more An Unsteady force generation mechanisms (delayed stall, wake capture and rotational lift) during idealized hovering of insect flight at Reynolds number (Re) of 136 have been identified in this research. Dependence of flow physics on Re forms the basis of present study to observe the dependence of unsteady force generation mechanisms on Re. A systematic study has been carried out by increasing Re from 136 to 4000 to investigate persistence of delayed stall, wake capture and rotational lift phenomenon. Using the solution of 3D Navier-Stokes equations, the aerodynamic force and the detailed flow structure around the wing are obtained which can provide useful insights into mechanism of unsteady force generation during idealized hovering at Re=4000. After grid and Mach number sensitivity analysis, the results are compared with previous studies at Re=136 for the code validation. The aerodynamic force and flow structure of a wing performing hovering motion at Re=4000 is calculated by solving Navier-Stokes equations. Re=4000 is selected on the premise that the length scale (mean aerodynamic chord) becomes closer to a Micro Air Vehicle (MAV); furthermore 30 times increase in Re (from 136 to 4000) is considered sufficient to assess changes in flow physics while remaining in laminar flow regime. Calculations are conducted for idealized hovering motion during which stroke 1 is initiated in still air, followed by flipping motion for reversing the direction and then stroke 2 (similar to stroke 1 but in opposite direction). Results obtained from this research are helpful for future work where they can be compared with those obtained from actual wing kinematics to assess the impact of kinematics on unsteady mechanisms.
Journal of Applied Fluid Mechanics, 2017
Delayed stall is the most dominant lift enhancing factor in insect flapping motion. Micro air veh... more Delayed stall is the most dominant lift enhancing factor in insect flapping motion. Micro air vehicle operates at Reynolds number 10 4-10 5 ; slightly higher than the insects' Reynolds number (Re). In the present research, thefocus is to investigate "stall-absent" phenomenon at Re representative of the micro air vehicles, the effect of spanwiseflow on the leading edge vortex and also to study the effect of geometry variations on the aerodynamic performance of the wing in unsteady motion. Corrugated dragonfly airfoil with rectangular wing planform is used, however, with wing kinematics restricted to azimuth rotation only. Three-dimensionalfinitevolume method is used, through commercial software Fluent, to numerically solve time-dependent incompressible Navier-Stokes equations. Computed results at Re 34000 and 100,000 reveal the same phenomenon of delayed stall, as observed in the case of insects. Furthermore, the performance of flat plate, profiled and corrugated wing in a sweeping motion at a high angle of attack is also compared.
Crashworthiness study of UCAV’s main landing gear using explicit dynamics
International Journal of Crashworthiness, 2022
Flow Angularity and Swirl Flow Analysis on Transonic Compressor Rotor by 1-Dimensional Dynamic Turbine Engine Compressor Code and CFD Analysis
Fluid Dynamics, 2021
Abstract— The performance and stability of a low-bypass turbofan transonic axial compressor with ... more Abstract— The performance and stability of a low-bypass turbofan transonic axial compressor with a nonuniform inlet flow is a significant concern in recent times. In both military and commercial aircraft, serpentine ducts produce significant inlet swirl distortion. Moreover, the nonuniform inlet flow frequently acts upon aircraft gas-turbine engines causing deteriorating effects on the aircraft engine. High circumferential swirl flows and inlet flow angularity decrease the aerodynamic performance and the stall margin and increase the rotor blade loading. The current paper is aimed at the investigation of the flow field in the tip clearance region of low-bypass turbofan transonic compressor rotor under nonuniform circumferential flow conditions through numerical simulation using Ansys CFX. The mathematical models based on 1D Mean Line Code and Dynamic Turbine Engine Compressor Code (DYNTECC) are used to analyze the nonuniform inlet swirl flow of the compressor rotor. The mathematical model is limited to compute the multistage compressor characteristics for the compression system and the combustor of a turbine engine. For the single-stage swirl flow analysis current paper focuses on the CFD based results. The results based on CFD show that co-swirl patterns slightly improve the stability range of the compressor; counter-swirl flows diminish it.
Existence of a lift plateau for airfoils pitching at rapid pitching rates
Computational Fluid and Solid Mechanics, 2001
Effects of Different Thickness Variation Strategies on Dynamic Stall in an Oscillating Airfoil
3rd AIAA Flow Control Conference, 2006
An active flow control technique has been a challenge for aeronautical engineers since the beginn... more An active flow control technique has been a challenge for aeronautical engineers since the beginning of flight. One of the more modern ideas is that of adaptive airfoils where the airfoil itself changes shape in response to flow conditions. In this research a code was modified to incorporate ...
TRANSITION PREDICTION IN LOW PRESSURE TURBINE (LPT) USING GAMMA THETA MODEL & PASSIVE CONTROL OF SEPARATION
The boundary layer of low-pressure turbine blades has received a great deal of attention due to a... more The boundary layer of low-pressure turbine blades has received a great deal of attention due to advent of high lift and ultra high lift LP turbines. At cruising condition, Reynolds number is very low in engine and LP turbine performance suffers mainly from losses due to the laminar separation bubble on suction surface. In this paper, T106A low pressure turbine profile has been used to study the behavior of boundary layer and subsequently, flow is controlled using the passive technique. Unsteady Reynolds Averaged Navier Stokes equations were solved using SST Gamma-Theta transition model for turbulence closure. Hybrid mesh topology has been used to discretize the computational domain, with highly resolved structured mesh in boundary layer (Y < 1) and unstructured mesh in the rest of domain. Simulations were performed using commercial CFD code ANSYS FLUENT ® at Reynolds number 91000 (based on inlet velocity and chord length) and turbulence intensity of 0.4%. To study the effect of d...
Prediction of Non-Uniform Distorted Flows, Effects on Transonic Compressor Using CFD, Regression Analysis and Artificial Neural Networks
Uploads
Papers by hossein hamdani