別紙41 (課程博士(英文))Date of submission (month day, yea":January 6,2022
D179103

MechanicalEn目lneerlng
PP11Caη1"s nameiyoshilida

StudentlD

Departmcnlof

NumberSuperⅥSors

UjiNakamura
iroshiYokoyama

Nmie onogi

Abstract (Doctor)
Title ofThesis

Analysis for Jet Fluctuation and Acoustic Radiation of "ute・Like lnstr山ηents

Approx.80o wm'ds
To elucidatethe mechanismby which the radiated sound changes with conditions ofblowing andthe instrument's shapes, this study performed numericalsimulations and exP田'iments simulating

actual conditions. Focusing on the interaction between the airaow and the sound of aute'1ikeinstruments, this study proposed an analytical method for sound chan曾es taking into accountthe

jet de臼.ection observed in the simulations. The effects of the jet deaection on the harmonic
Structure and its mechanism were also clari丘edFirst, an analyticalmethod for quanti6,ingjet auctuations was proposed to determine conditions
Ofblowing or instrument shapes that mainly contributes to sound changes. This method was first
Utilized in the recorder, which has fewer variable parameters of blowin曾 than the aute. TO

decompose jetauctuations into an acoustic and a auid dynamic osci11ation, a f01'mula representsjet
auctuations was proposed by modi67ing the Fletcher's formula (44SA,1976) based on the jetauctuations predicted by direct aeroacoustic simulations. This formula takes into account theinitial amplitude at the exit and the jet deaection toward the ed又e, which were obS田'ved in theSimulations. The jet auctuations in the simulations were represented by this foTmula, and theCharacteristics ofauctuations (the convection velocity, the ampli6.cation rate, the acoustic feedback

effects, and the actualjet offset) were quanti6ed. As a result, the difference in the mode
Predominancy seems to be pToduced by the difference in the amplification rate probably due to adifference of exit shape (strai今ht・ or arch・shaped). This analytical method seems to be useful forinvestigatin牙 mechanisms ofsound changes

Second, the effects of the jet an曾le (an牙le between the jet and the mouth openin宮) on theharmonic structure and their mechanism were shown for the flute. The jet an曾le is an additional

Parameter for the aute, whereas it is genera11y 6Xed to zero in the recorder. The effects haveremained unclear. This study compared the effects of jet angle with those of other parameters

Within a practical range. Blowin宮 Parameters were varled independently by an artificial blowin宮
device with reference to the actual blowin今 Condition measured for a aute player. The radiatedSound showed that the effects ofthe jet an曾le on the harmonic structure is less than those ofthe jet

Offset and almost equal with those ofthe flow rate and comparably lar晉er than the distance. Themechanism forthe change ofharmonic structure with thejet angle wasinvesti牙ated from the aow

負eld measured W北h a hot、wire anemometer.1n this measurement, the jet offset was flxed to zero.
Periodicaljet auctuations were determined by phase'avera牙ing the measured values to quanti丘
the characteristics ofjet auctuations. As a result, with increasin套 the jet angle (the jet direction
approaches verticalto the mouth opening), the jet was found to deaect more inside. Due to thedeaection, the actualjet offset was found to decrease with increasin宮 the jet angle. This decrease ofthe actualjet offset was almost、§onsistent with the change of harmonic structure with the jetangle. The amplitude of the second and the third mode of jet fluctuations can also affect theharmonic structure; however, the amplitude was found to affect little. The variation of theharmonic structure with the jet an宮le seems to be mainly caused by the change of the actualjet
Offset due to the jet deaection.
Third, the mechanism of the jet deaection was investi又ated by direct aeroacoustic simulations,reproducin牙 the shapes of the aute head joint and the oral caV北y used in the experiments. The
acoustic and the aoW 6elds were investi今ated for the two jet offsets (the relative height of the jetfrom the ed曾e). The acoustic field showed that △SPL increases as the actualjet offset increases.
This tendency is consistent with the experiments. The velocity vector in the aow field showed that,
When the jet deflects inward, the jet is bent toward the inner wa11 and aows alon牙 the waⅡ due tothe coanda effect on the jet、 As the jet offset decreases, the distance between the jet and the edge
increases. This can increase the air entrained into the jet and thus the coanda effect. Due to theCoanda effect, the jet is drawn to the inner wa11, which possibly promotes the outward movement
Ofthe jet. As the jet offset decreases, the coanda effect seems to increase, resuHin宮 in the outward
deaection ofthe jet. AISO, the distance between the jet and the edge chan曾es with the jet angle. Theinward deaection ofthe jet when increasing the jet angle, which is observed in the second work, isProbably caused by the decrease ofthe coanda effect,