Konvektif sınır tabakanın kuramsal ve deneysel incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 39426
- Danışmanlar: PROF.DR. SÜREYYA ÖNEY
- Tez Türü: Yüksek Lisans
- Konular: Meteoroloji, Meteorology
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 63
Özet
ÖZET Bu çalışmada planörcülük ve diğer hava sporları için büyük önem taşıyan, konvektif sınır tabakada gerçekleşen konveksiyonla birlikte bazı meteorolojik parametrelerin düşey ve/veya yatay değişimleri deneysel ve teorik olarak incelenmiştir. Termik ve plume (huzme), sırasıyla süreksiz ve sürekli olarak yeryüzeyinden yükselen, çevre havaya nazaran daha yüksek sıcaklık ve aynı zamanda pozitif düşey hızlalara (yukarıya doğru) sahip olan bireysel hava kütleleridir. Bunların başlangıç yarıçapları 10-30 metreden 200- 300 metreye kadar değişebilir. Güçleri de bununla doğru orantılı olarak artmaktadır. Yeterince güçlü olanlar yoğunlaşma seviyesine kadar yükselebilmekte ve burada yoğunlaşıp konvektif (kümülüform tipi) bulutlar meydana getirmektedirler. Çalışmayla ilgili ölçümler 14 Eylül-2 Ekim 1992 tarihleri arasında İnönü (Eskişehir) Hava Eğitim Merkezi'nde gerçekleştirilmiştir. Ayrıca Ankara radyosonde istasyonu verileri düşey olarak interpole edilerek 1. Boyutlu Plume Modelinde girdi verisi olarak kullanılmıştır. Ancak modelin hata payını azaltmak amacıyla yer seviyesi verisi olarak İnönü'de ölçülen değerler kullanılmıştır. Bu çalışmada Baker ve Jensen (1987) tarafından öneri len Konvektif Plume Bulut Modeli geliştirilerek konvektif bir bulut altındaki plume içerisindeki düşey hız ve sıcaklığın düşey değişimi hesaplanmaya çalışılmış, model sonuçlarıyla ölçümler karşılaştırılmıştır. Kuru termik öngörüsü için ikinci bir model“Termik Uçuş öngörüsü Modeli”İnönü'de uygulanmış ve model sonuçları gözlem ve ölçümlerle karşılaştırılmıştır. Ayrıca planör ile yapılan ölçümlerde mümkün olduğu kadar sabit seviye uçuşu yapılarak termik bölgelerinin tespitine çalışılmış ve bu bölgelerde sıcaklık ile düşey hız değişimleri arasındaki iliş ki incelenmiştir. Yukarıda söz edilen her iki modelden elde edilen sonuçlarla gözlemlerin oldukça iyi uyum gösterdikleri görülmüş, gözlemlerle sonuçlar arasındaki ortalama bağıl hata değerlerinin 0.005 ile 0.58 arasında değiştiği belirlenmiştir. Çalışma sayısı artırılıp yine aynı ölçüde uyumlu sonuçlar bulunması halinde her iki modelin oldukça başarılı sonuçlar almak üzere uygulanabileceği söylenebilir; her iki model de bu alandaki çalışmaların devamını destekler niteliktedir. iv-
Özet (Çeviri)
THEORETICAL AMD EXPERIMENTAL ANALYSIS OF CONVECTIVE BOUNDARY LAYER SUMMARY The vertical and regional variations of some meteorological parameters in a convective boundary layer have experimentally and theoretically been analised in the thesis. The convective activities which are observed in the convective boundary layer have a great importance for gliding and also for other sportive flights. These convective activities are generally observed into two different kinds as thermals and plumes. Thermals are individual air masses and continouosly rise from heated surface. Plumes have in succesive source of heated surface. There are positive vertical motions in thermals and plumes. Their initial radius may vary from few ten meters to few hundred meters. Their strength is directly proportional with their radius. Some of thermals gain sufficient energy to rise up to the condensation level and become cumulus clouds that contain water particles. Some energy discharged by the condensing water particles is redistributed within the forming cloud and creates an inner mechanism of motion which is called the cumulus circulation. Due to solar heating of the ground, convective elements are released and rise until they reach a stable atmospheric layer, the inversion. While ascending thermals experience turbulent lateral entrainment of surrounding air their moisture content become modified as well as their temperature. In order to describe this convection, vertical profiles of temperature, moisture, and wind are needed. The profiles are permenantly changed by synoptic processes such as large scale subsidence or ascent, horizontal advection and by convection itself. Ascending and descending convective elements accomplish the turbulent transport of sensible and latent heat and momentum. Heating of the ground is influenced by a great number of parameters: Available insolation depends on latitude, season and time of day, cloud cover and turbidity. On the other hand the exposure of the surface and characteristics of the soil (type, albedo, moisture content and vegetation) determine the amount of heat which is finally driving thermic convection. Precise measurements of structure and dynamics of thermals are difficult, because of the size of areas and column heights to be scanned through in the relatively short lifetime of a thermal with about 20 or 40 minutes. A statistical description of shape and velocity of thermal can contribute to the general view on their characteristics that has been measured by Lindemann (1978). -V-This thesis is intended to be a second attempt to initiate the cumulus convection studies by flight observations in Turkey. The first study was carried out in Eskişehir (İnönü) between 1983 and 1987, (Öney, Aslan, Peremeci and Adalı, 1987). The main goal of the second attempt is to study of the microphysical and dynamical structure of thermals and plumes below cumulus clouds by using the different measuring systems and theoretical models. The specific purpose of the thesis can be listed as below: i) To investigate the thermic potential of İnönü where the only and most of the important field for training and flying activities of Turkey is, ii) To develop a new forecasting model for predicting the thermic convection and preparing the best flight plan, For these two main goals of the study some meteorological paremeters i.e. dry and wet-bulb temperature and flight data i.e. flight speed, altitude and vertical velocity of glider have been measured within or in the vicinity of thermals and cumulus clouds by flying with Wilga airplanes or Puchacz-SZD-50 gliders in Eskişehir- Turkish Air League Flight Training Center between 14th of September and 2nd of October, 1992. The gliding and other air-sports and their meteorological requirements are studied in the first chapter of the thesis. Flight using gliders and other aircrafts which have little or no self propulsion has special meteorological requirements. A pilot flying by such an aircraft has to use or avoid particular meteorological phenomena. To be fully effective, his capabilities must include ability to interpret the meteorological information he recieves and observes. The meteorological forecasting methods does not cover the entire range of air sports but they can be applied on gliding, hang gliding, paragliding and hot air balloning. Forecasting for airsports requires at least an elementary knowledge of the aircraft characteristics. Sailplanes are mostly made of reinforced plastic metarial. Some are of metal. All sailplanes have ailerons, rudder and elevator controls, as for larger powered aircraft. Sailplanes do not neassarily have to be lightweight aircraft. Most modern types can accomodate water ballast. High performance gliders have a fully retractable wheel. For competition and record purposes gliders are classified according to several criteria, the most apperent being wing span. Hang gliders are lightweigh aircrafts made of high quality alloy aluminium tubing with a fabric covered wing. Training can be given with single place hang gliders, but two-place training is more common. -vi-Paragliding is probably the simplest way of flying. The equipment is basically a parachute which in contrast to regular parachutes has a rectangular wing-like form with integrated air chambers. These chambers inflate when the pilot rapidly moves the parachute against the wind. During the flight the chambers keep filled with air and supply enough lift for soaring. Gliders, hang gliders, motor gliders and microlight aircraft normally have air speed indicators, altimeters and particularly sensitive variometers (rate of climb and descent indicators) and compasses. This instrumentation is often augmented with electronic aids and audio aids to hear rather then look at variometer data. For many years recording barographs have been used to produce height-time graphs for flights. Digital recording barographs can now be used for post flight computer aided. analysis, if required. More sophisticated equipment is also used for digitally recording and analysing more detailed and specific information, including air temperature and humidity associated with thermals and other features of meteorological interest along a flight path. There is already enough air sports aircraft with such equipment to obtain data for feed-back into meteorological study. For safety, satisfaction and success, an airsports pilot requires aircraft characteristics and meteorological conditions such that she or he can: - manage the aircraft on the ground, before and after flight, - take off, - remain airborne with the aid of usable upcurrents, - avoid or get out of weather hazards, especially hazardous vertical currents, - be within gliding range of a suitable landing place, - plan a safe approach to landing and touchdown. The nature of the meteorological requirements may deduced from the aircraft characteristics and operational types of flying. This thesis is related with the detail of the meteorological requirements and practice of gliding. The details have been presented in Chapters 2, 3 and 4. The horizontal scale has been generally changed between 200 km and 1000 km. The second chapter of this study begins with the definition of thermal convection. The motion of a thermal may be described by similarity solutions to the governing equations. The initial characteristics of the thermal are; dp : the deviation of the density in a thermal from that of its surroundings, p : the density of thermic, g : acceleration due to gravity, z : height above the level of growth, r : radius of the thermic. -VII-In therms of these parameters, the buoyancy force per unit mass is given by, P e where dd is the potential temperature deviation, 6 the potential temperature and b the buoyancy. Vertical velocity of a thermal (w) is given by, _ 1 W°C(gBz) * where C is proportionality constant. Experiments were performed by Scorer to determine the proportionality constants. Stommel presented a cumulus model which incorporated the effect of mixing through a steady jet at the cloud base with that of enrainment at the sides of the cloud. The entrainments rate can be computed as, Entrainment rate= A i^=2« M dz i where M is mass of the plume, the entrainment constant are determined as a =0.1. For thermal theory, it is equal to 0.25 (0.2). The energy relesed in the plume or a thermal must somehow be related to the mass inflow at the base. In the third chapter, the experimental techniques used are presented for determining the location of the thermals. The first boundary layer sounding is performed early morning, between 7:30 and 9:00 a.m. with a tow aircraft. The vertical variation of temperature is measured with a termocouple mounted on the frontal part of the aircraft. The temperature values and altitudes are recorded on a tape for every 30 meters of height increments. These measurement are considered as input parameters for one of the theoretical models. During the glider flights between 2:30 and 4:00 p.m., vertical air velocities and available maximum flight heights are recorded. These measurements are compared to the model which details are presented in the forth chapter. To compare the temperature and vertical velocity variations in and in the near vicinity of thermals, the constant height flight with the Puchacz-SZD- 50 Glider have been carried out and the data are recorded every 30 seconds. The accuracy of temperature measuring system is 5%, and it is also a digital system. All data is recorded on a tape. Some details related with the flight path and other meteorological observations are also recorded on a tape-casette. Two different models have been discussed in the fourth chapter. The first model is called as“Thermal Fly Forecasting Model”. The model gives weather the meteorological concitions are favourable for soaring. The input paremeters are: Early morning soundings of air temperature, at three levels successively 1800, 2700 and 3600 meters above m.s.l., the expected maximum surface temperature, and differences between maximum and minimumu air temperature of previous day. The nomograph used in this method and the detailed steps of method are presented in -VIII-the same chapter. Four different nomographes have been used for different periods of the year. The results are compared with observations and presented at the fifth chapter. The second model presented in this study is a computer model called“One-Dimensional Plume Model”. The variations of microphysical and dynamic parameters below convective clouds are being discussed in the fourth chapter. The equations for the model are considered in two groups: i ) Equations for environmental air, ii) Equations inside a plume. For every Dz=20 meters air layer, all the parameters are interpolated by using the following equation: Y= [(Y2-Y1)/(X2-X1)]XX+[X2.Y1-X1.Y2]/(X2-X1) Vertical variation of the temperature inside a plume is given as: Tc(i+l)=Tc(i)+(dT/dz)Dz Where Dz is the layer thickness. The total water content, vertical velocity, plume radius and pressure equations are given as below: qtc(i+l)= qtc(i)+(dqtc/dz)Dz W(i+1)= W(i) + (dw/dz)Dz r(i+l)= r(i) + (
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