Aeroacoustics: an interesting combination between aerodynamics and acoustics

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This morning I was listening a beautiful sound of an aeolian harp from the Youtube. It’s so naturally relaxing and it’s perfect for me to get my mind fresh for the day. This sound was amazingly tuned by the size (diameter) of the string (infinite circular cylinder) and the level of wind speed. In aeroacoustic engineering, they named this airborne noise mechanism as an aeolian tone. It’s actually a dipole type of sound radiation.

Aeolian harp sound radiation is different from the sound radiation from a loudspeaker (monopole) or noise from the engine jet (quadrupole).  The sound sources of aeolian harp consist of two monopole sources of equal strength, but they are in opposite phase. The two sources are located very close to each other when compared to its sound wavelength.

We can control this sound beautifully. Using Lighthill’s acoustic analogy and Curle’s equation for the inclusion the effect of aeolian tone,  we can see how the aeolian tones is controlled by just using a thin flat plate. Please visit my publications if you like to see more.

 

 

 

Vortex Induced Vibration

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For the last few days I’ve tried to simulate flow over a circular cylinder at Re=22k using OpenFOAM. The cylinder is attached to a mass-damping system in one degree of freedom (cross-stream). The simulation only success when the natural frequency of the system is high, omega_o >= 2 x vortex shedding frequency. I believe that I need to work out on the resonant response of the system.

AIAA news: Analyst Not Overly Concerned By Dreamliner Issues.

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The Los Angeles Times (12/25, Hennigan) reported the Boeing 787 “has run into another bout of turbulence with fresh concerns about its safety.” While there has been “criticism of the problem-plagued program,” aviation industry consultant Scott Hamilton “said that the latest Dreamliner problems are ‘irritants more than substance.'” Boeing was also noted by the article as not being overly concerned by the issues.

Boeing Hits 787. 747-8 Delivery Targets. The Wall Street Journal (12/22, Ostrower, Subscription Publication) reported that despite some early production issues, Boeing has hit its delivery targets for both the 787 and 747-8. According to the article, reaching these targets was very important for the company following several years of not hitting them due to design problems.

AIAA news: Apollo 17 Commander Concerned About Pilots’ Flying Skills.

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Aviation International News (11/6, Mark) reports, “Apollo 17 commander Gene Cernan said he worries about the flying skills of pilots today.” He remarked, “I worry about the complacency that technology is imposing on pilots. Pilots tend to become overwhelmed with all the lights on these glass panels and forget they still have a responsibility to fly the airplane.” Meanwhile, “Cernan believes that part of the solution is pilots being honest about their flying skills and their shortcomings.”

AIAA news: Mayor Says Atlanta Police Helicopter Had Been Refurbished Before Fatal Crash.

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The AP (11/6, Compton) reports, “The Atlanta police helicopter that crashed and killed two officers on board had been completely refurbished within the last decade, and its pilot and maintenance crew were confident it was safe to fly, officials said Monday.” The helicopter crashed Saturday as the officers were looking for a missing 9-year-old boy. The department did have “a newer chopper, but Atlanta Mayor Kasim Reed said the veteran pilot who had been flying for 16 years preferred the older model because it was easy to maneuver.” It was still unknown “if the fallen officers had been using night vision, though Deputy Chief Renee Propes said pilots often rely on their sight alone, even at night.”

AIAA’s news: China Successfully Tests Jet Fighter.

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RIA Novosti (11/1) reports, “China successfully completed a test flight on Wednesday of its new fifth-generation J-31 jet fighter, according to the Huanqiu Shibao newspaper.” The piece notes that “the flight represents a crucial step for the Chinese military, which has become only the third in the world – after the United States and Russia – to have developed a stealthy fifth-generation fighter aircraft.”

Wired (11/1, Axe) reports, “Fortunately for Washington, the acceleration of Beijing’s stealth program comes just as the U.S. Air Force is restoring its beleaguered F-22s to full service amid problems with their oxygen systems – and as the delayed, over-budget and technically troubled F-35 is finally showing some testing progress. In recent weeks the F-35 has refueled mid-air, released a missile and flown at night with its finicky helmet sight.”

AIAA’s news: ORBITEC’s Vortex Liquid Fuel Rocket Engine Successfully Tested.

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Gizmag (11/2, Dodson) reports, “Orbital Technologies Corporation (ORBITEC) successfully flight tested its patented vortex liquid fuel rocket engine on October 25. … The flight established substantial progress toward ORBITEC’s development of a 30,000-lb (13,600-kg) thrust vortex engine for the US Air Force Advanced Upper Stage Engine Program and for NASA’s Space Launch System.”

Basic OpenFOAM workshop

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BrochureCFD_workshop

 

Dear All,

Thank you for your support and participations at the Basic OpenFOAM workshop. We’re planning to organise a series of similar workshop (increase in complexity) in the near future. Please be updated with any news on this. Our aim is to promote the use of OpenFOAM locally and providing a platform for discussion and knowledge sharing among the OpenFOAM community in Malaysia. If you have suggestion on how we can go for that, please don’t hesitate to drop me an email.

 

Cheers,

Mohamed Sukri Mat Ali (MJIIT) and Low Lee Leong (UNITEN)

Tel: +603- 22031286

Two papers about passive flow and noise control have been accepted for publications

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A simple but effective passive wake and noise control for bluff body applications, e.g., high rise buildings, side view mirror of passenger cars, landing gear system of aircrafts and etc., can be made practically possible by introducing a small flat plate downstream of the bluff bodies. [International Journal of Heat and Fluid Flow, and AIAA Journal]