Читать книгу Introduction to Flight Testing - James W. Gregory - Страница 33
2.2.3 Temperature
ОглавлениеTemperature at any given point in the Earth's atmosphere will depend not only on the altitude but also on time of year, latitude, and local weather conditions. Since the variation of temperature has spatial, temporal, and stochastic input, the development of the standard atmosphere as a function of only altitude inherently involves many approximations. Thus, we might anticipate that the actual temperature at a given location can deviate significantly from the standard value.
The standard temperature profile has been determined through an average of significant amounts of data from sounding balloons launched multiple times a day over a period of many years, at locations around the globe. The resulting temperature profile is a function of geopotential altitude, with the lapse rate, a = dT/dh, representing the linear variation of temperature with altitude for each region (see Table 2.1 and Figure 2.3). In the troposphere (0 ≤ h ≤ 11 km), the standard temperature lapse rate is defined as −6.5 K/km, starting at TSL = 288.15 K. In the lower portion of the stratosphere (11 < h ≤ 20 km), the temperature is presumed to be constant at 216.65 K. Starting at 20 km, the temperature then increases at a rate of 1 K/km due to ozone heating of the upper stratosphere. Based on the data in Table 2.1, we can write expressions for the temperature profile throughout the standard atmosphere as
where “ref” refers to the base of the layer (defined by either sea level conditions, or the top of the prior atmospheric layer, working upwards). Output from Eq. (2.10) can be stacked for each altitude layer, one on top of another, to define the entire standard temperature profile. Since most flight testing, especially for light aircraft and drones, occurs at altitudes below 20 km, we will focus our attention on the troposphere and lower portion of the stratosphere.
Table 2.1 Definition of temperature lapse rates in various regions of the atmosphere.
Source: Data from NOAA et al. 1976.
| Region | h1(km) | h2(km) | a = dT/dh(K/km) |
|---|---|---|---|
| Troposphere | 0 | 11 | −6.5 |
| Stratosphere | 11 | 20 | 0.0 |
| 20 | 32 | 1.0 | |
| 32 | 47 | 2.8 | |
| 47 | 51 | 0.0 | |
| Mesosphere | 51 | 71 | −2.8 |
| 71 | 84.852 | −2.0 |
h1 and h2 are the beginning and ending altitudes of each region, respectively.
Figure 2.3 Standard temperature profile.
